The Caltech Experiment That Proved How Life Copies Itself

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I love reading New York Times obituaries, not because of any morbid fascination with death, but because they offer a window into extraordinary lives that might otherwise go unnoticed. These tributes often highlight people whose work had real impact, even if their names were never widely known. Unlike the celebrity coverage that fills so much of the media, these obituaries can be quietly riveting, full of depth, insight, and genuine accomplishment.

For two years I managed the New York Times video obituary series called Last Word. We interviewed people of high accomplishment who had made a difference in the world BEFORE they died, thus giving them a chance, at a latter age (in our case 75 was the youngest, but more often people would be in their 80s) to tell their own stories about their lives. They signed an agreement acknowledging that the interview would not be shown until after their death. Hence the series title: Last Word. Anyway, when I ran the program, I produced video obituaries for people as varied as Neil Simon, Hugh Hefner, Sandra Day O’Connor, Philip Roth, Edward Albee, and my favorite, the great Harvard biologist E.O. Wilson. Spending time and learning about their lives in their own words was a joy.

All of that is to say that obituaries often reveal the lives and accomplishments of people who have changed the world. These are stories that might never be told so thoughtfully or thoroughly anywhere else.

*California Institute of Technology (Photo: Erik Olsen)*

Which bring us to a quiet lab at Caltech in 1958, where two young biologists performed what some still call “the most beautiful experiment in biology”. Their names were Matthew Meselson and Franklin Stahl, and what they uncovered helped confirm the foundational model of modern genetics. With a simple centrifuge, a dash of heavy nitrogen, and a bold hypothesis, they confirmed how DNA, life’s instruction manual, copies itself. And all of it took place right here in California at one of the world’s preeminent scientific institutions: the California Institute of Technology or CalTech, in Pasadena. The state is blessed to have so many great scientific minds and institutions where people work intensely, often in obscurity, to uncover the secrets of life and the universe.

Franklin Stahl died recently at his home in Oregon, where he had spent much of his career teaching and researching genetics. The New York Times obituary offered a thoughtful account of his life and work, capturing his contributions to science with typical respect. But after reading it, I realized I still didn’t fully grasp the experiment that made him famous, the Meselson-Stahl experiment, the one he conducted with Matthew Meselson at Caltech. It was mentioned, of course, but not explained in a way that brought its brilliance to life. So I decided to dig a little deeper.

Franklin Stahl in an undated photo. (Cold Spring Harbor Laboratory Library and Archives)

The Meselson-Stahl experiment didn’t just prove a point. It told a story about how knowledge is built: carefully, creatively, and with a precision that leaves no room for doubt. It became a model for how science can answer big questions with simple, clean logic and careful experimentation. And it all happened in California.

Let’s back up: When Watson and Crick proposed their now-famous double helix structure of DNA in 1953 (with significant, poorly recognized help from Rosalind Franklin), they also suggested a theory about how it might replicate. Their idea was that DNA separates into two strands, and each strand acts as a template to build a new one. That would mean each new DNA molecule is made of one old strand and one new. It was called the semi-conservative model. But there were other theories too. One proposed that the entire double helix stayed together and served as a model for building an entirely new molecule, leaving the original untouched. Another suggested that DNA might break apart and reassemble in fragments, mixing old and new in chunks. These were all plausible ideas. But only one could be true.

Watson and Crick with their model of the DNA molecule (Photo: A Barrington Brown/Gonville & Caius College/Science Photo Library)

To find out, Meselson and Stahl grew E. coli bacteria in a medium containing heavy nitrogen (nitrogen is a key component of DNA), a stable isotope that made the DNA denser than normal. After several generations, all the bacterial DNA was fully “heavy.” Then they transferred the bacteria into a medium with normal nitrogen and let them divide. After one generation, they spun the DNA in a centrifuge that separated it by weight. If DNA copied itself conservatively, the centrifuge would show two bands: one heavy, one light. If it was semi-conservative, it would show a single band at an intermediate weight. When they performed the experiment, the result was clear. There was only one band, right between the two expected extremes. One generation later, the DNA split into two bands: one light, one intermediate. The semi-conservative model was correct.

Their results were published in Proceedings of the National Academy of Sciences in 1958 and sent shockwaves through the biological sciences.

Meselson and Stahl experiment in diagram.

To me, the experiment brought to mind the work of Gregor Mendel, an Augustinian monk who, in the mid-1800s, quietly conducted his experiments in the garden of a monastery in Brno, now part of the Czech Republic. By breeding pea plants and meticulously tracking their traits over generations, Mendel discovered the basic principles of heredity, dominant and recessive traits, segregation, and independent assortment, decades before the word “gene” even existed. Like Mendel’s experiments, the Meselson-Stahl study was striking in its simplicity and clarity. Mendel revealed the rules; Meselson and Stahl uncovered the mechanism.

There’s a fantastic video where the two men discuss the experiment that is worth watching. It was produced produced by iBiology, part of the nonprofit Science Communication Lab in Berkeley. In it Meselson remembered how the intellectual climate of CalTech at the time was one of taking bold steps, not with the idea of making a profit, but for the sheer joy of discovery: “We could do whatever we wanted,” he says. “It was very unusual for such young guys to do such an important experiment.”

Most people think of Caltech as a temple of physics. It’s where Einstein lectured, where the Jet Propulsion Laboratory was born (CalTech still runs it), and where the gravitational waves that rippled through spacetime were detected. But Caltech has a quieter legacy in biology. Its biologists were among the first to take on the structure and function of molecules inside cells. The institute helped shape molecular biology as a new discipline at a time when biology was still often considered a descriptive science. Long before Silicon Valley made biotech a household term, breakthroughs in genetics and neurobiology were already happening in Southern California.

Meselson and Stahl in the iBiology video (Screen grab: Science Communication Lab)

The Meselson-Stahl experiment is still taught in biology classrooms (my high school age daughter knew of it) because of how perfectly it answered the question it set out to ask. It was elegant, efficient, and unmistakably clear. And it showed how a well-constructed experiment can illuminate a fundamental truth. Their discovery laid the groundwork for everything from cancer research to forensic DNA analysis to CRISPR gene editing. Any time a scientist edits a gene or maps a mutation, they are relying on that basic understanding of how DNA replicates.

In a time when science often feels far too complex, messy, or inaccessible, the Meselson-Stahl experiment is a reminder that some of the most important discoveries are also the simplest. Think Occam’s Razor. Two young scientists, some nitrogen, a centrifuge, a clever idea, and a result that changed biology forever.

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Manzanitas are California’s Sculptured Survivors

At Inspiration Point, Yosemite, sticky whiteleaf manzanita tends to occupy south slopes, greenleaf manzanita tends to occupy north slopes. (Photo: NPS)

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As an avid hiker in Southern California, I’ve become a deep admirer of the chaparral that carpets so many of the hills and mountains in the region. When I was younger, I didn’t think much of these plants. They seemed dry, brittle, and uninviting, and they’d often leave nasty red scrapes on your legs if you ever ventured off-trail.

But I’ve come to respect them, not only because they’ve proven to be remarkably hardy, but because when you look closer, they reveal a kind of beauty I failed to appreciate when I was younger. I’ve written here and elsewhere about a few of them: the fascinating history of the toyon (Heteromeles arbutifolia), also known as California holly, which likely inspired the name Hollywood and is now officially recognized as Los Angeles’ native city plant; the incredible durability of creosote bush, featured in a recent Green Planet episode with David Attenborough; and the laurel sumac, whose taco-shaped leaves help it survive the region’s brutal summer heat.

Manzanita branches in the high Sierra. The deep red colored bark enhanced by water. (Photo: Erik Olsen)

But there’s another plant I’ve come to admire, one that stands out not just for its resilience but for its deep red bark and often gnarled, sculptural form. It’s manzanita, sometimes called the Jewel of the Chaparral, and it might be one of the most quietly extraordinary plants in California.

If you’ve ever hiked a sun-baked ridge or wandered a chaparral trail, chances are you’ve brushed past a manzanita. With twisting, muscular limbs the color of stained terra cotta and bark so smooth it looks hand-polished, manzanita doesn’t just grow. It sculpts itself into the landscape, twisting and bending with the contours of hillsides, rocks, and other plants.

There are more than 60 species and subspecies of manzanita (Arctostaphylos), and most are found only in California. Some stand tall like small trees as much as 30 feet high; others crawl low along rocky slopes. But all of them are masters of survival. Their small, leathery leaves are coated with a waxy film to lock in moisture during the long dry seasons. They bloom in late winter with tiny pink or white bell-shaped flowers, feeding early pollinators when little else is flowering. By springtime, those flowers ripen into red fruits: the “little apples” that give the plant its name.

Manzanita flowers (Santa Barbara Botanical Garden)

One of manzanita’s more fascinating traits is how it deals with dead wood. Instead of dropping old branches, it often retains them, letting new growth seal off or grow around the dead tissue. You’ll see branches striped with gray and red, or dead limbs still anchored to the plant. It’s a survival strategy, conserving water, limiting exposure, and creating the twisted, sculptural forms that make manzanita distinctive.

And fire is key to understanding manzanita’s world. Like many California plants, many manzanita species are fire-adapted: some die in flames but leave behind seeds that only germinate after exposure to heat or smoke. Others resprout from underground burls after burning. Either way, manzanita is often one of the first plants to return to the land after a wildfire, along with laurel sumac, stabilizing the soil, feeding animals (and people), and shading the way for the next wave of regrowth.

Manzanita’s astonishing red bark The reddish color of manzanita bark is primarily due to tannins, naturally occurring compounds that also contribute to the bark’s bitter taste and deter insects and other organisms from feeding on it. (Photo: NPS)

Botanically, manzanitas are a bit of a mystery. They readily hybridize and evolve in isolation, which means there are tiny populations of hyper-local species, some found only on a single hill or canyon slope. That makes them incredibly interesting to scientists and especially vulnerable to development and climate change.

Their red bark is the result of high concentrations of tannins, bitter compounds that serve as a natural defense. Tannins are present in many plants like oaks, walnuts and grapes, and in manzanitas, they make the bark unpalatable to insects and animals and help resist bacteria, fungi, and decay. The bark often peels away in thin sheets, shedding microbes and exposing fresh layers underneath. It’s a protective skin, both chemical and physical, built for survival in the dry, fire-prone landscapes of California.

Whiteleaf manzanita leaves and berries (Photo: NPS)

The plants still have mysteries that are being uncovered. For example, a new species of manzanita was only just discovered in early 2024, growing in a rugged canyon in San Diego County. Named Arctostaphylos nipumu to honor the Nipomo Mesa where it was discovered and its indigenous heritage, it had gone unnoticed despite being located just 35 miles from the coast and not far from populated areas. The discovery, announced by botanists at UC Riverside, highlights that unique species localization, as the plants are found sometimes growing only on a single ridge or in a specific type of soil. Unfortunately, this newly identified species is already at risk due to development pressures and habitat loss. According to researchers, only about 50 individuals are known to exist in the wild, making A. nipumu one of California’s rarest native plants, and a reminder that the story of manzanita is still unfolding, even in places we think we know well.

A new species of manzanita – *A. nipumu* – was discovered in San Diego County last year (2024), surprising reserachers. (Photo: UCR)

For hikers, photographers, and anyone with an eye for the unusual, manzanita is a cool plant to stumble upon. I will often stop and admire a particularly striking plant. I love when its smooth bark peels back in delicate curls, looking like sunburned skin or shavings of polished cinnamon. It’s hard to walk past a manzanita without reaching out to touch that smooth, cool bark. That irresistible texture may not serve any evolutionary purpose for the plant, but it’s one more reason to wander into California’s fragrant chaparral, where more species of manzanita grow than anywhere else on Earth.

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California’s Wild Laboratory and The Evolutionary Wonders of the Channel Islands

Anacapa Island in California’s Channel Islands (Photo: Erik Olsen)

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I recently took two scuba diving trips out to the Channel Islands to investigate and help remove ghost lobster traps: abandoned or lost gear that poses a serious threat to marine life. While out there, I also had a chance to explore the marine protected areas surrounding Anacapa and Santa Cruz Islands, getting a firsthand look at how these underwater reserves are helping to restore ocean health and marine life (another story on that coming). Diving in the Channel Islands is a great way for certified divers to experience the incredible biodiversity of California’s coastal waters, even if the water is cold as hell.

The Channel Islands are actually relatively close to the California mainland, just 12 miles from Ventura in the case of Anacapa. But the wild and windswept chain feels like a world apart. On a clear day, you can see them from Ventura or Santa Barbara, but oddly, few people actually visit. Compared to other national parks, they remain relatively unknown, which only adds to their quiet allure. Sometimes called the “Galápagos of North America,” these eight islands are a refuge for wildlife and a place where evolution unfolds before your eyes.

U.S. Park Service rangers patrol the marine protected area off of Anacapa Island in California’s Channel Islands
(Photo: Erik Olsen)

(Here’s a cool bit of history: there are eight Channel Islands today, but 20,000 years ago, during the last ice age when sea levels were much lower, four of them—San Miguel, Santa Rosa, Santa Cruz, and Anacapa—were connected as a single landmass called Santarosae.)

For scientists and nature lovers, the Channel Islands are more than just scenic, they’re a natural laboratory. Each island has its own shape, size, and ecological personality, shaped by millions of years of isolation. That makes them an ideal setting for the study of island biogeography, the branch of biology that looks at how species evolve and interact in isolated environments. What happens here offers insight into how life changes and adapts not just on islands, but across the planet.

Island biogeography is anchored in the theory proposed by E.O. Wilson and Robert MacArthur in the 1960s. Their theory, focusing on the balance between immigration and extinction of species on islands, is brilliantly exemplified in the Channel Islands.

The Channel Islands’ rich mosaic of habitats, from windswept cliffs and rocky shores to chaparral-covered hillsides and dense offshore kelp forests, provides an ideal setting for studying how species adapt to varied and changing conditions. Each island functions like a separate ecological experiment, shaped by isolation, resource limits, and time. Evolution has had free rein here, tweaking species in subtle ways and, occasionally, producing striking changes.

One of the most significant studies conducted in the Channel Islands focused on the island fox (Urocyon littoralis), a species found nowhere else on Earth. Research led by the late evolutionary biologist Robert Wayne at UCLA and others showed that the fox populations on each of the six islands they inhabit have evolved in isolation, with distinct genetic lineages and physical traits. This makes them a remarkable example of rapid evolution and adaptive divergence, core processes in island biogeography.

Genetic analyses revealed that each island’s fox population carries unique genetic markers, shaped by long-term separation and adaptation to local environments. These differences aren’t just genetic, they’re physical and behavioral too. Foxes on smaller islands, for instance, tend to be smaller in body size, likely an evolutionary response to limited resources, a phenomenon known as insular dwarfism. Variations in diet, foraging behavior, and even coat coloration have been documented, offering scientists an unparalleled opportunity to study evolutionary processes in a real-world, relatively contained setting.

Excavation of pygmy mammoth bones on the Channel Islands (Photo: National Park Service)

This phenomenon of insular dwarfism isn’t unique to the island fox. One of the most striking examples from the Channel Islands is the pygmy mammoth (Mammuthus exilis), whose fossilized remains were discovered on Santa Rosa Island. Evolving from the much larger Columbian mammoth, these ancient giants shrank to about half their original size after becoming isolated on the islands during the last Ice Age. Limited food, reduced predation, and restricted space drove their dramatic transformation, a powerful illustration of how isolation and environmental pressures can reshape even the largest of species.

Furthermore, the Channel Islands have been instrumental in studying plant species’ colonization and adaptation. Due to their isolation, the islands host a variety of endemic plant species. Research by Kaius Helenurm, including genetic studies on species such as the Santa Cruz Island buckwheat (Eriogonum arborescens) and island mallow (Malva assurgentiflora), has shown how these plants have adapted to the islands’ unique environmental pressures and limited gene flow.

Island mallow (*Malva assurgentiflora*), a vibrant flowering plant found only on the Channel Islands, thrives in the harsh coastal environment—its striking blooms a testament to the power of isolation and adaptation. (Photo: Curtis Clark)

The islands have been a scientific boon to researchers over the decades because they are not only home to many diverse and endemic species, but their proximity to the urban centers and the universities of California make them amazingly accessible. It’s been suggested that if Darwin had landed on the Channel Islands, he arguably could have come up with the theory of natural selection off of California, rather than happening upon the Galapagos. A 2019 book about the islands, titled North America’s Galapagos: The Historic Channel Islands Biological Survey recounts the story of a group of researchers, naturalists, adventurers, cooks, and scientifically curious teenagers who came together on the islands in the late 1930s to embark upon a series of ambitious scientific expeditions never before attempted.

The Channel Islands are renowned for their high levels of endemism — species that are found nowhere else in the world. This is a hallmark of island biogeography, as isolated landmasses often lead to the development of unique species. Darwin’s On the Origin of Species was one of the first extensive efforts to describe this phenomenon. For example, as mentioned above, the Channel Islands are home to the island fox (Urocyon littoralis), a small carnivore found only here. Each island has its own subspecies of the fox, differing slightly in size and genetics, a striking example of adaptive radiation, where a single species gives rise to multiple different forms in response to isolation and environmental pressures. That said, the foxes are also incredibly cute, but can be rather annoying if you are camping on the islands because they will ransack your food stores if you do not keep them tightly closed.

Island Fox on Santa Cruz Island (photo: Erik Olsen)

Bird life on the Channel Islands also reveals remarkable diversity and endemism. Much like the finches of the Galápagos, these islands are home to distinct avian species shaped by isolation and adaptation. The Santa Cruz Island Scrub Jay, for instance, is noticeably larger and more vividly colored than its mainland relatives, a reflection of its unique island habitat. Also, jays in pine forests tend to have longer, shallower bills, while those in oak woodlands have shorter, deeper bills. Evolutionary adaptations right out of the Darwinian playbook. Likewise, the San Clemente House Finch has evolved traits suited to its specific environment, illustrating how even common species can diverge dramatically when given time and separation.

The Island Scrub-Jay (*Aphelocoma insularis*), found only on Santa Cruz Island, is larger and more vividly colored than its mainland cousin—an unmistakable symbol of how isolation shapes evolution. (Photo: National Park Service)

The impacts of invasive species on island ecosystems, another critical aspect of island biogeography, are also evident in the Channel Islands. The islands have been an superb laboratory for the practice of conservation and human-driven species recovery. For example, efforts to remove invasive species, like pigs and rats, and the subsequent recovery of native species, like the island fox, provide real-time insights into ecological restoration and the resilience of island ecosystems.

These efforts at conservation and species recovery extend beyond the island fox. In 1997, the U.S. Fish and Wildlife Service identified that 13 plant species native to the northern Channel Islands in California were in dire need of protection under the Endangered Species Act. This need arose due to several decades of habitat degradation, primarily attributed to extensive sheep grazing. These conservation efforts have yielded good news. For instance, the island bedstraw (Galium buxifolium) expanded from 19 known sites with approximately 500–600 individuals in 1997 to 42 sites with over 15,700 individuals. Similarly, the Santa Cruz Island dudleya (Dudleya nesiotica) population stabilized at around 120,000 plants. As a result of these recoveries, both species were removed from the federal endangered species list in 2023, coinciding with the 50th anniversary of the Endangered Species Act.

Santa Cruz Island Dudleya (Photo: National Park Service)

Conservation efforts at the Channel Islands extend beneath the waves, where marine protected areas (MPAs) have played a crucial role in restoring the rich biodiversity of the underwater world. I’ve seen the rich abundance of sea life firsthand on several dives at the Channel Islands, where the biodiversity feels noticeably greater than at many mainland dive sites in Southern California.

The Channel Islands Marine Protected Areas (MPAs), established in 2003, were among the first of their kind in California. The MPAs around Anacapa, Santa Cruz, and other islands act as refuges where fishing and other extractive activities are limited or prohibited, allowing marine ecosystems to recover and thrive. Over the past two decades, scientists have documented increases in the size and abundance of key species such as kelp bass, lobsters, and sheephead, alongside the resurgence of lush kelp forests that anchor a vibrant web of marine life. These protections have not only benefited wildlife but have also created living laboratories for researchers to study ecological resilience, predator-prey dynamics, and the long-term impacts of marine conservation, all taking place in the context of island biogeography.

Kelp bass in the kelp forest at the Channel Islands (Photo: Erik Olsen)

What makes all of this possible is the remarkable decision to keep these islands protected and undeveloped. Unlike much of the California coast, the Channel Islands were set aside, managed by the National Park Service and NOAA as both a national park and a marine sanctuary. These protections have preserved not just the landscapes, but the evolutionary stories still unfolding in real time. It’s a rare and precious thing to have a living laboratory of biodiversity right in our backyard, and a powerful reminder of why preserving wild places matters.

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The Scourge of Ghost Lobster Traps and the Battle to Save Marine Life in California

Ghost lobster trap off Santa Cruz Island in California’s Channel Islands (Photo: Erik Olsen)

Lobster is delicious. Let’s just get that out of the way. Yes, I’m sure there are some who either don’t enjoy the taste of this prolific crustacean, or who are allergic, but for my part, lobster (with a small vial of melted butter) is ambrosia from the sea.

But beyond its place on the plate, the California spiny lobster plays a vital ecological role: hunting sea urchins, hiding in rocky reefs, and helping to keep kelp forests in balance. Its value extends far beyond what it fetches at market. But beneath the surface, particularly around the Channel Islands lurks a growing problem that doesn’t just threaten lobsters. It threatens the entire marine ecosystem: ghost traps.

Dive ship Spectre off of Anacapa Island in California’s Channel Islands (Photo: Erik Olsen)

In Southern California, lobster fishing is both a cultural tradition and a thriving industry, worth an estimated $44 million annually to California’s economy from commercial landings as well as recreational fishing, tourism, and seafood markets.

In late April, I traveled to the Channel Islands with my colleague Tod Mesirow to see the problem of ghost lobster traps firsthand. We were aboard the Spectre dive ship and pulled out of Ventura Harbor on an overcast morning, the sky a uniform gray that blurred the line between sea and cloud. The swell was gentle, but the air carried a sense of anticipati on. We were invited by the Benioff Ocean Science Laboratory, which is conducting research and outreach in the area. Our visit took us to Anacapa and Santa Cruz Islands, where I would be diving to observe the traps littering the sea floor. Tod, meanwhile, remained topside, capturing footage and speaking with marine scientists. Even before entering the water, we could see the toll: frayed lines tangled in kelp, buoys adrift, and entire areas where dive teams had marked clusters of lost gear.

California spiny lobsters alive when the ghost trap was recovered (Photo: Erik Olsen)

Ghost traps are lobster pots that have been lost or abandoned at sea. Made of durable metal mesh and often outfitted with bait containers and strong ropes, these traps are built to last. And they do. For years. Sometimes decades. The problem is, even when their human operators are long gone, these traps keep fishing.

“It’s not uncommon to find multiple animals dead inside a single trap,” said Douglas McCauley, a marine science professor at UC Santa Barbara and director of the Benioff Ocean Science Laboratory who was onboard with us and leading the project. “It’s heartbreaking. These traps are still doing exactly what they were built to do, just without anyone coming back to check them.”

Douglas McCauley, director of the Benioff Ocean Science Laboratory at the University of California Santa Barbara holding a lobster caught in a ghost trap off the coast of the Channel Islands (Photo: Erik Olsen)

Around the Channel Islands National Marine Sanctuary, where fishing pressure is high and waters can be rough, thousands of traps are lost every season. Currents, storms, or boat propellers can sever buoys from their lines, leaving the traps invisible and unrecoverable. Yet they keep doing what they were designed to do: lure lobsters and other sea creatures inside, where they die and become bait for the next unfortunate animal. It’s a vicious cycle known as “ghost fishing.”

“They call them ghost traps because, like a ghost sailing ship, they keep doing their thing. They keep fishing.” said McCauley.

Statewide, the numbers are staggering. Approximately 6,500 traps are reported lost off the California coast each fishing season, according to The California Department of Fish and Wildlife. The folks at the Benioff Ocean Science Laboratory said as many as 6,000 may lie off the coast of the Channel Islands alone. Ocean Divers removing marine debris have found traps stacked three and four high in underwater ravines—rusting, tangled, but still deadly. These ghost traps don’t just catch lobsters; they also trap protected species like sheephead, cabezon, octopuses, and even the occasional sea turtle or diving seabird.

Diver and Project Scientist Chase Brewster of the Benioff Ocean Science Laboratory collecting data on ghost lobster traps near California’s Channel Islands (Photo: Erik Olsen)

Nowhere is this more evident than around the Channel Islands. These rugged islands are home to some of California’s richest kelp forests and underwater canyons. The islands and their surrounding waters are home to over 2,000 plant and animal species, with 145 of them being unique to the islands and found nowhere else on Earth. In fact, the Channel Islands are often referred to as North America’s Galapagos for the immense diversity of species here.

The islands are also the site of the state’s most productive spiny lobster fisheries. Every fall, hundreds of commercial and recreational fishers flood the area, setting thousands of traps in a race to catch California spiny lobsters (Panulirus interruptus). But rough swells and heavy gear mean traps go missing. Boats sometimes cut the lines of traps, making them near impossible to retrieve from the surface. And because this region is a patchwork of state waters, federal waters, and marine protected areas (MPAs), cleanup and regulation are anything but straightforward.

California Spiny Lobster off Anacapa Island (Photo: Erik Olsen)

The traps are often difficult to locate, partly because of their remote placement and the notoriously rough waters around the Channel Islands. But the Benioff Ocean Science Laboratory has a powerful asset: side scan sonar. From the ship, they can scan and map the seafloor, where the ghost traps often appear as dark, rectangular shapes against the sand. Once spotted, the team uses GPS to log their exact location.

“It’s creates a picture made of sound on the seafloor and you see these large lego blocks staring at you in bright yellow on the screen and those are your lobster traps,” sayd McCauley. “There’s nothing else except a ghost trap that looks like that.”

Plunging into the frigid waters off Santa Cruz Island was a jolt to the system. Visibility was limited, just 10 to 15 feet, but I followed two scientists from the Benioff Ocean Science Laboratory down to a depth of 45 feet. Their task: to attach a rope to the trap so it could be hauled up by the boat’s winch.

Dive ship Spectre off the coast of Santa Cruz Island in California’s Channel Islands (Photo: Erik Olsen)

The water was thick with suspended particles, the light dimming quickly as we dropped lower. My 7mm wetsuit was just barely enough to stave off the cold. On the seafloor, the ghost trap emerged, a large rectangular cage resting dark and ominous in the sand. And it was teeming with life. Fish darted around its edges, lobsters clambered along the frame, and inside, several animals moved about, trapped and slowly dying. It was easy to see how a single trap could wreak quiet havoc for years.

California law technically requires all lobster traps to include biodegradable “escape panels” with zinc hinges that degrade over time, eventually allowing trapped animals to escape. But enforcement is tricky, and the panels don’t always work as intended. In practice, many traps, especially older or illegally modified ones, keep fishing long after they should have stopped. That’s what we were out here to find.

A baby octopus caught in a ghost trap in the waters off California’s Channel Islands (Photo: Erik Olsen)

Complicating matters is the fact that once a trap goes missing, there’s no easy way to retrieve it. Fishers are not legally allowed to touch traps that aren’t theirs, even if they’re obviously abandoned. And while a few small nonprofits and volunteer dive teams conduct periodic ghost gear removal missions, they can’t keep pace with the scale of the problem.

“At this fishery, we can’t get them all,” says McCauley. “But by going through and getting some species out and getting them back in the water, we’re making a difference. But in the process, we’re coming up with new ideas, new technologies, new research methods, which we think could play a role in and actually stopping this problem in the first instance.”

Once abundant along California’s coast, this large abalone spotted off Santa Cruz Island is a rare sight today—a quiet reminder of how overfishing, disease, and environmental change have decimated their populations. (Photo: Erik Olsen)

Back topside, the recovery team aboard the Spectre used a powerful hydraulic winch to haul the trap onto the deck. After climbing out of the cold water, still shivering, I joined the others to get a closer look. The trap was heavy and foul-smelling, but what stood out most was what was inside: lobsters, maybe ten or more. Some had perished, but many were alive and thrashed their tails when lifted by the scientists. Females could be identified by their broader, flatter tail fins—adapted to hold eggs. The team carefully measured each one before tossing them back into the sea, the lobsters flipping backward through the air and disappearing into the depths.

There were other animals, too. Large, rounded crabs known as Sheep crabs, common to these waters, scuttled at the bottom of the trap. Sea snails were clustered along the mesh, and in one cage, there were dozens of them, clinging and crawling with slow purpose. Even baby octopuses made appearances, slithering out onto the deck like confused aliens. I picked one up gently, marveling at its strange, intelligent eyes and soft, shifting forms, before tossing it back into the sea in hopes it would have another chance at life.

Ghost lobster trap lies on the seafloor off of Santa Cruz Island in California’s Channel Islands (Photo: Erik Olsen)

By then, the day had brightened and the sun had come out, easing the chill that lingered after the dive. The traps would be taken back to Ventura, where they’d likely be documented and disposed of. But this day wasn’t just about saving individual animals or pulling traps off the seafloor—it was about data. The Benioff team wants to understand just how big of a problem ghost traps really are. It’s not just about the number of traps lost each season, but the broader ecological toll: how many animals get caught, how many die, and how these traps alter the underwater food web. Every recovered trap adds a piece to the puzzle. This trip was about science as much as rescue.

State agencies, including the California Department of Fish and Wildlife (CDFW), have started pilot programs aimed at tackling ghost gear. In 2023, CDFW launched a limited recovery permit program that allows fishers to collect derelict traps at the end of the season, provided they notify the state. But participation is voluntary and poorly funded.

Elsewhere, states like Maine and Florida have created large-scale, state-funded programs to identify and remove ghost traps, often employing fishers in the off-season. California, despite having the nation’s fourth-largest lobster fishery, has yet to make a similar investment.

Ghost lobster traps recovered from the seafloor off the coast of California’s Channel Islands (Photo: Erik Olsen)

Some solutions are already within reach. Mandating GPS-equipped buoys for commercial traps could help track and retrieve gear before it’s lost. More robust escape hatch designs, made from materials that dissolve in weeks rather than months, would shorten the lifespan of a lost trap. And expanding retrieval programs with funding from fishing license fees or federal grants could make a big dent in ghost gear accumulation.

But even more powerful than regulation may be public awareness. Ghost traps are out of sight, but their damage is far from invisible. Every trap left behind in the Channel Islands’ waters becomes another threat to biodiversity, another source of plastic and metal waste, and another reminder that marine stewardship doesn’t stop when the fishing season ends.

Key to the whole effort is data:

“Every one of the animals that we put back in the water today, we’ll be taking a measure,” says McCauley. “After a little bit of crunching in the lab, we’ll be able to say, oh, actually, you know, every single trap undercuts the fishery by x percent for every single year that we don’t solve the problem.”

Doug McCauley with a lobster trap retrieved from the seafloor off the coast of California’s Channel Islands (Photo: Erik Olsen)

As we headed back toward Ventura, Tod and I talked with Douglas McCauley and Project Scientist Neil Nathan from the Benioff Ocean Science Laboratory. The team had collected a total of 13 traps that day alone, and 34 over the several days they’d been out. There was a sense of satisfaction on board, quiet but real. Each trap removed was a small win for the ecosystem, a little less pressure on an already strained marine environment.

“I would call today an incredible success, ” said Neil Nathan. “Feeling great about the number of traps we collected.”

California has long been a leader in ocean conservation. If it wants to stay that way, it needs to take ghost fishing seriously, not just around the Channel Islands, but up and down the coast. After all, we owe it to the lobsters, yes, but also to the underwater forests, reef communities, and countless species whose lives are tangled in the nets we leave behind.

The Fight for California’s Coastline and the Future of the Coastal Commission

For over 50 years, the California Coastal Commission has protected public access and natural beauty, but growing challenges—wildfires, housing shortages, and political pressure—are testing its authority like never before.

California Coast at Big Sur (Erik Olsen)

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Having lived for nearly 20 years on the East Coast, I’ve witnessed firsthand how vast stretches of coastline have been heavily developed, often turning pristine shores into exclusive enclaves inaccessible to the general public. In the latter half of the 20th century, America saw a surge in coastal development, driving beachfront property values to unprecedented heights. This boom was accompanied by exclusionary practices from coastal property owners and municipalities, limiting access and reinforcing barriers to the shore. From gated beachfront mansions in the Hamptons to private communities along the Jersey Shore, not to mention the vast development of the coast of Florida (Carl Hiaasen shout out!), many coastal areas are reserved for a privileged few, limiting public access and enjoyment of natural spaces. In stark contrast, California learned from these mistakes early on, adopting a fundamentally different approach focused on keeping its coastline accessible and preserved for everyone.

Many beaches in the Hamptons are private. Unlike California, which has strong public access protections under the *California Coastal Act*, New York follows a mix of public and private beach ownership laws. In the Hamptons, beachfront property owners often hold rights extending to the high tide line, meaning much of the sandy shore is off-limits to the general public.

This ethic of preservation and accessibility has profoundly shaped California’s coastal policies and given rise to institutions specifically tasked with safeguarding the shore. The ethic of preserving California’s coast stretches back more than a century, championed by early conservationists like Julia Platt, a pioneering marine biologist and activist. Platt was a fascinating figure, and we previously covered her story, which you can read here. In the late 19th and early 20th centuries, Monterey’s coastline was being ravaged by sardine canneries and industrial operations that polluted the bay and threatened marine life. Defying societal barriers, Platt became mayor of Pacific Grove in 1931 and secured public control over the town’s intertidal zones, ensuring their protection from commercial exploitation.

Hovden Cannery, 886 Cannery Row, Monterey, Monterey County, CA (Library of Congress)

That ethic of appreciation and commitment to coastal preservation remained deeply embedded in California’s identity as the state moved into the 20th century. By the 1970s, this consciousness transformed into action, leading to formal protections that would shape the coastline for generations. Spanning approximately 840 miles from San Diego’s sun-drenched shores to the wild, windswept cliffs of Crescent City, California’s coastline did not remain protected and accessible by accident. It was the result of a concerted effort to safeguard its natural beauty and ensure public access—an effort that culminated in the establishment of the California Coastal Commission, a state agency created to oversee and enforce these critical protections.

The Coastal Commission’s story began in 1972 amid growing environmental awareness and concerns about unchecked development. California residents, alarmed by the threat of losing their treasured coastline to developers, launched grassroots campaigns resulting in Proposition 20—the Coastal Initiative. This public referendum created the Coastal Commission initially as a temporary regulatory body.

Senate President pro-tem Jim Mills led a bicycle tour of the coast from San Francisco to San Diego, stopping for press conferences and public events in coastal communities along the route. (Credit: California Coastal Commission)

In 1976, recognizing the importance of long-term coastal preservation, the California Legislature passed the Coastal Act, permanently institutionalizing the Coastal Commission and its values (values shared by a majority of Californians, I should add). Key legislative figures included Assemblymember Alan Sieroty and Senator Jerry Smith. Peter Douglas, a passionate advocate for environmental justice who later became the Commission’s long-serving Executive Director, was instrumental in drafting the Coastal Act. Born in Berlin and fleeing Nazi Germany during World War II, Douglas’s personal experiences deeply influenced his dedication to environmental protection. One of his most lasting statements about the coast is, “The coast is never saved, it is always being saved.” (Makes for a good T-shirt.)

Peter M. Douglas (1942–2012) was an environmental activist, UCLA law graduate, and key author of Proposition 20, which established the California Coastal Commission. He co-authored the 1976 Coastal Act and served as its Executive Director for 26 years.
(University of California, Berkeley)

Under Douglas’s leadership, which spanned from 1985 until his retirement in 2011, the Coastal Commission achieved significant conservation victories. One landmark success was securing public access to Malibu’s Broad Beach in 1981, previously restricted to wealthy homeowners (many of them famous celebrities). Similarly, the Commission prevented extensive development of Orange County’s Bolsa Chica Wetlands, preserving this crucial ecological habitat and protecting numerous bird and marine species. Also in Orange County, the historic cottages at Crystal Cove State Park were preserved as affordable accommodations rather than being transformed into a luxury resort. Douglas was tenacious and stubborn in his efforts to protect the coast. He was “the world’s best bureaucratic street fighter,” according to Steve Blank, a member of the commission, who spoke to The New York Times in 2010.

Crystal Cove’s unspoiled coastline remains protected thanks to the California Coastal Commission’s efforts to preserve both its natural beauty and fragile ecosystems. Once threatened by development, this stretch of shoreline continues to thrive as a sanctuary for marine life and a place for the public to experience California’s coast as it once was. (Photo: Erik Olsen)

Perhaps the Commission’s most publicized battle was with billionaire Vinod Khosla over Martins Beach near Half Moon Bay. After purchasing land surrounding the beach in 2008, Khosla closed the access road, igniting a lengthy legal fight. The Commission, alongside advocacy groups, successfully argued that public beach access must be maintained, culminating in court decisions mandating the reopening of Martins Beach to the public. It was a significant affirmation of the public’s coastal rights.

Khosla became something of a vilified figure, perhaps for a good reason. As of March 2025, the legal dispute over public access to Martins Beach continues. In May 2024, San Mateo County Superior Court Judge Raymond Swope ruled that the lawsuit filed by the California State Lands Commission and the California Coastal Commission against Khosla could proceed. The state agencies argue that, based on the public’s longstanding use of the beach, access should remain open under the legal doctrine of implied dedication.

Vinod Khosla speaks at South by Southwest 2024 (Wikipedia)

Beyond these high-profile victories, the Commission diligently protects scenic coastal views by regulating construction along vulnerable bluffs, safeguarding habitats for endangered species like the California least tern and the Western snowy plover. The significance of this protection extends far beyond simply claiming a spot on the sand or catching a wave. The California coast is a global treasure trove of biodiversity, shaped by the collision of cold and warm ocean currents, rugged geology, and an array of microclimates. Its kelp forests, some of the most productive ecosystems on Earth, form towering underwater cathedrals that shelter fish, sea otters, and invertebrates while sequestering carbon and buffering coastal erosion. Tide pools teem with anemones, sea stars, and scuttling crabs, while offshore waters host migrating gray whales, pods of orcas, and dolphin super pods. Few places on Earth does such a dramatic convergence of oceanic and terrestrial life create a living laboratory as dynamic, fragile, and irreplaceable as California’s coastline.

Safeguarding these resources has always been a core part of the Coastal Commission’s mission. Yet, the Commission’s broad regulatory authority hasn’t been without controversy (understatement alert!). In fact, there’s been a lot over the years, and in particular right now. Critics argue it often overreaches, impacting private property rights and overriding local governance. Property owners have faced severe challenges due to stringent permit requirements and mandatory easements for public access. Furthermore, vast amounts of red tape have often contributed to delays and higher costs, fueling tension between environmental protection and economic development, particularly in the context of California’s ongoing housing crisis. The commission’s plans for managed retreat in response to coastal erosion have sparked ongoing concern among coastal property owners.

Elephant seal colony at San Simeon (Erik Olsen)

Jeff Jennings, the mayor of Malibu commented: “The commission basically tells us what to do, and we’re expected to do it. And in many cases that extends down to the smallest details imaginable, like what color you paint your houses, what kind of light bulbs you can use in certain places.

The challenges of balancing conservation with development have become even more urgent in the face of devastating wildfires, such as the Palisades Fire. This historically destructive blaze burned numerous homes along the coast, leaving behind not only physical devastation but also a complex and expensive rebuilding process. Restoring these communities requires immense resources, regulatory approvals, and long-term planning, raising questions about whether the Coastal Commission is up to the task.

Stretch of Malibu destroyed in the Palisades fire (Erik Olsen)

Even Governor Gavin Newsom has been critical of the Commission, citing delays and bureaucracy that may hinder swift rebuilding efforts. The ongoing tension between preserving the natural environment and addressing the needs of displaced residents continues to test the Commission’s authority and effectiveness. Before dismantling the Commission and stripping it of its authority as the guardian of the coast, we must ask ourselves what it would mean to lose an agency that has stood for public access, environmental protection, and coastal preservation for over 50 years. The consequences of weakening its influence could reshape California’s coastline in ways that future generations may come to regret.

The California Coastal Commission has 12 voting members and 3 non-voting members, appointed by the Governor, the Speaker of the Assembly, and the Senate Rules Committee. Six of these are locally elected officials, and six are public members. They are supported by key figures like Executive Director Kate Huckelbridge (the first woman to lead the California Coastal Commission in its 50-year history) and Chair Justin Cummings. However, the Commission now faces mounting pressure as it navigates growing criticism over its efficiency and decision-making. Some argue that the Commission has become too rigid, impeding much-needed development, while others warn that weakening its authority would open the door to rampant privatization and environmental degradation. Surely, there is a middle ground?

But before dismantling an institution that has served as California’s coastal safeguard for over five decades, we must fully understand what is at stake. The California Coastal Commission has played a crucial role in preserving public access, protecting natural habitats, and maintaining the scenic beauty of the shoreline. Its legacy is visible in the open beaches, thriving wetlands, and untouched bluffs that define the state’s coastline. Stripping away its influence could have lasting consequences, reshaping California’s shorelines in ways that future generations may find irreversible and regrettable. Changes to the Commission’s authority may be necessary, at least temporarily, to expedite rebuilding efforts for those who have lost their homes. However, we must be cautious about how much power is stripped away, ensuring that any reforms do not undermine the very protections that have kept California’s coast open and preserved for decades.

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Salt to Salvation: The Desalination Revolution in California’s Drought Battle

Visibly low water conditions at Shasta Lake in Shasta County, on October 13, 2022.
Andrew Innerarity / California Department of Water Resources.

Water, water, every where, nor any drop to drink.

— Samuel Taylor Coleridge’s poem The Rime of the Ancient Mariner.

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Desalination, the process of turning seawater into potable water, is gaining traction as a viable solution to California’s perennial drought issues. The Golden State, with its sprawling 850-mile coastline and notorious aridity, is primed for desalination to play a pivotal role in its water management strategies.

The mission of the Seawater Desalination Test Facility in Port Hueneme, Ventura. John Chacon / California Department of Water Resources

California’s history with droughts is long and storied, with the state experiencing some of its driest years on record recently. Traditional sources of water, such as snowpacks and reservoirs, have become increasingly unreliable due to the erratic patterns of climate change. While an atmospheric river storm in 2023 and several powerful storms in 2024 and 2025 significantly eased California’s drought conditions for the time being, there is widespread concern that serious drought conditions will soon return and become the new norm.

As a response, several desalination plants have emerged along the coast. One notable example is the Claude “Bud” Lewis Carlsbad Desalination Plant in San Diego County, which is the largest in the Western Hemisphere, providing about 50 million gallons of drinking water daily.

Every day, 100 million gallons of seawater pass through semi-permeable membranes, producing 50 million gallons of fresh water delivered directly to municipal users. The Carlsbad plant, which has been fully operational since 2015, now provides roughly 10 percent of the freshwater supply used by the region’s 3.1 million residents—although at nearly double the cost of water from the region’s primary alternative sources.

Claude “Bud” Lewis Carlsbad Desalination Plant (Photo courtesy of Carlsbad Desalination Project)

Desalination is not just a process but a symphony of advanced technologies working in concert. The most prevalent method used in California is reverse osmosis (RO). RO employs a semi-permeable membrane that allows water molecules to pass through while blocking salt and other impurities. This membrane is the linchpin of the operation, designed to withstand the high pressures necessary to reverse the natural process of osmosis where normally, water would move from a low-solute concentration to a high-solute concentration.

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Reverse osmosis desalination is an energy-intensive process, one that demands a significant amount of power to be effective. At its core, the technique involves forcing seawater through a semi-permeable membrane to separate salt and other minerals, yielding fresh water. This process, however, requires substantial pressure, much higher than the natural osmotic pressure of seawater, to push the water through the membrane. Achieving and maintaining this pressure consumes a considerable amount of energy. Furthermore, the energy demands are compounded by the need for constant system maintenance and the treatment of the highly saline brine that’s left over. This energy requirement is a key challenge in making reverse osmosis desalination a more widespread solution for water scarcity, as it not only increases operational costs but also has environmental implications, especially if the energy comes from non-renewable sources.

John Chacon / California Department of Water Resources

The science behind these membranes is fascinating. They are not just filters; they are engineered at the molecular level. The membranes are typically made from polyamide, created through complex chemical reactions that result in a thin film where the magic happens. Water molecules navigate through this film via tiny pores, leaving behind salts and minerals.

This scientific marvel, however, has additional environmental challenges. Along with the vast energy needs of reverse osmosis, there are also concerns about water pollution. Brine, which is the concentrated saltwater byproduct, must be carefully managed to avoid harming marine ecosystems when it’s discharged back into the ocean.

Charles E. Meyer Desalination Plant in Santa Barbara, California, plays a key role in improving water reliability and resiliency during the drought years. Florence Low / California Department of Water Resources.

Innovations continue to improve the technology, aiming to make desalination more energy-efficient and environmentally friendly. New approaches such as forward osmosis, which uses a natural osmotic pressure difference rather than mechanical pressure, and the use of alternative energies like solar and wind power are on the horizon. There’s also ongoing research into biomimetic membranes, inspired by nature’s own filtration systems, such as those found in the roots of mangrove trees or in the kidneys of animals.

In addition to the sprawling, successful desalination plant in Carlsbad, numerous other projects are on the way. The Doheny Ocean Desalination Project, located in Dana Point, has seen a significant increase in projected costs but is still moving forward. It’s expected to be completed by 2027 and will provide about 5 million gallons of drinking water daily to residents in Orange County.

In November, the California Coastal Commission greenlit a permit for the Monterey Bay Area Desalination Plant, a vast $330 million seawater desalination plant in Marina, a modest city of 22,500 people located roughly 15 minutes north of the more prosperous Monterey. The proposed Cal-Am desalination facility, if finalized, is set to produce 4.8 million gallons of fresh water daily.

Monterey Bay at Moss Landing, California. Photo: Erik Olsen

However, Marina’s Mayor, Bruce Delgado, stands in opposition to the project. He argues that it would alter the character of Marina and negatively impact its natural surroundings. Delgado contends that while his city would shoulder the environmental and industrial impacts of the plant, the adjacent, wealthier areas such as Carmel-by-the-Sea, Pacific Grove, and Pebble Beach would enjoy most of the benefits.

In February 2024, the California Department of Water Resources (DWR) released a report identifying future brackish water desalination projects to enhance the state’s water reliability. The report aims to meet goals outlined in California’s Water Supply Strategy: Adapting to a Hotter, Drier Future, which targets increasing water supply by implementing new brackish desalination projects providing 28,000 acre-feet per year by 2030 and 84,000 acre-feet per year by 2040.

As California looks to the future, the role of desalination is poised to expand. The state’s water plan includes the potential for more desalination facilities, particularly in coastal cities that are most affected by drought and have direct access to the sea. The integration of desalination technology with California’s complex water infrastructure speaks to a broader trend of marrying innovation with necessity.

The implications for drought-prone regions extend beyond just survival; they encompass the sustainability of ecosystems, economies, and communities. While desalination is not a panacea for all of California’s water woes, it represents a critical piece of the puzzle in the quest for water security in an era of uncertainty. As the technology advances, it may well become a cornerstone of how humanity adapts to a changing climate, making what was once undrinkable, a wellspring of life.

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Berkeley’s Cosmic Breakthrough and the Alvarez Discovery That Rewrote Earth’s History

Artist’s rendering of the colossal Chicxulub meteor hurtling toward Earth, moments before impact on the Yucatán Peninsula, an event that reshaped life on our planet 66 million years ago. (Erik Olsen)

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It is no coincidence that “Eureka” is the state motto of California. From its founding, the state has been a hub of groundbreaking discoveries, from the Gold Rush to advancements in space exploration, the rise of Silicon Valley and the development of modern computing, the development of seismic science, and the confirmation of the accelerating expansion of the universe. But one discovery made at the University of California, Berkeley, changed the way we see the world—or at least how it was almost destroyed, along with a huge part of life on the planet.

In 1977, Walter Alvarez arrived at Berkeley with rock samples from a small Italian town called Gubbio, unaware that they would help rewrite the history of life on Earth. He had spent years studying plate tectonics, but his father, Luis Alvarez, a Nobel Prize-winning physicist known for his unorthodox problem-solving at Berkeley, would propel him into a new kind of investigation, one deeply rooted in geology and Earth sciences. Their work led to one of the most significant scientific breakthroughs of the 20th century: the discovery that a massive meteorite impact was responsible for the extinction of the dinosaurs and much of life on Earth.

Luis and Walter Alvarez stand at the K–Pg boundary within the rock layers of a limestone outcrop near Gubbio, Italy, in 1981. This geological marker is linked to the asteroid impact that triggered the mass extinction 66 million years ago. (Lawrence Berkeley National Laboratory)

The samples Walter had collected contained a puzzling clay layer sandwiched between older and younger limestone deposits. This clay was rich in iridium—an element rare on Earth’s surface. The discovery of such an unusually high concentration of iridium in a single layer of buried rock was perplexing. Given that iridium is far more common in extraterrestrial bodies than on Earth’s surface, its presence suggested an extraordinary event—one that had no precedent in scientific understanding at the time. The implications were staggering: if this iridium had arrived all at once, it pointed to a cataclysmic event unlike anything previously considered in Earth’s history. Although some scientists had speculated about meteor impacts, solid evidence was scarce.

Alvarez determined that this layer corresponded precisely to the Cretaceous-Paleogene (K-Pg) boundary (formerly called Cretaceous–Tertiary or K–T boundary), the geological marker of the mass extinction that eradicated the non-avian dinosaurs 66 million years ago. Scientists had long debated the cause of this catastrophe, proposing theories ranging from volcanic activity to gradual climate change. But the Alvarez team would introduce a radical new idea—one that required looking beyond Earth.

Layers of sediment at Stevns Klint, Denmark, showcasing the distinct K–Pg boundary. The dark clay layer, rich in iridium, marks the asteroid impact that led to the mass extinction of the dinosaurs 66 million years ago. (UNESCO)

Mass extinctions stand out so distinctly in the fossil record that the very structure of geological time is based on them. In 1841, geologist John Phillips divided life’s history into three chapters: the Paleozoic, or “ancient life”; the Mesozoic, or “middle life”; and the Cenozoic, or “new life.” These divisions were based on abrupt breaks in the fossil record, the most striking of which were the end-Permian extinction and the end-Cretaceous extinction, noted here. The fossils from these three eras were so different that Phillips originally believed they reflected separate acts of creation. Charles Lyell, one of the founders of modern geology, observed a “chasm” in the fossil record at the end of the Cretaceous period, where species such as belemnites, ammonites, and rudist bivalves vanished entirely. However, Lyell and later Charles Darwin dismissed these apparent sudden extinctions as mere gaps in the fossil record, preferring the idea of slow, gradual change (known as gradualism, versus catastrophism). Darwin famously compared the fossil record to a book where only scattered pages and fragments of lines had been preserved, making abrupt transitions appear more dramatic than they were.

Luis Alvarez was a physicist whose career had spanned a remarkable range of disciplines, from particle physics to aviation radar to Cold War forensics. He had a history of bold ideas, from using muon detectors to search for hidden chambers in pyramids to testing ballistic theories in the Kennedy assassination with watermelons. When Walter shared his perplexing stratigraphic findings, Luis proposed a novel method to measure how long the clay layer had taken to form: by analyzing its iridium content.

A fossilized ammonite, one of many marine species that vanished at the K–Pg boundary, marking a sharp “chasm” in the fossil record after the asteroid impact 66 million years ago. (Photo: Erik Olsen)

As discusses, Iridium is a rare element on Earth’s surface but is far more abundant in meteorites. Luis hypothesized that if the clay had accumulated slowly over thousands or millions of years, it would contain only tiny traces of iridium from cosmic dust. But if it had been deposited rapidly—perhaps by a single catastrophic event—it might show an anomalously high concentration of the element. He reached out to a Berkeley colleague, Frank Asaro, whose lab had the sophisticated equipment necessary for this kind of analysis.

Nine months after submitting their samples, Walter received a call. Asaro had found something extraordinary: the iridium levels in the clay layer were off the charts—orders of magnitude higher than expected. No one knew what to make of this. Was it a weird anomaly, or something more significant? Walter flew to Denmark to collect some late-Cretaceous sediments from a set of limestone cliffs known as Stevns Klint. At Stevns Klint, the end of the Cretaceous period shows up as a layer of clay that’s jet black and contains high amounts of organic material, including remnants of ancient marine life. When the stinky Danish samples were analyzed, they, too, revealed astronomical levels of iridium. A third set of samples, from the South Island of New Zealand, also showed an iridium “spike” right at the end of the Cretaceous. Luis, according to a colleague, reacted to the news “like a shark smelling blood”; he sensed the opportunity for a great discovery.

Stevns Klint’s towering white chalk cliffs stand as a dramatic testament to Earth’s history, preserving the thin, dark Fish Clay layer that marks the cataclysmic asteroid impact that ended the age of dinosaurs 66 million years ago. (UNESCO)

The Alvarezes batted around theories. But all the ones they could think of either didn’t fit the available data or were ruled out by further tests. Then, finally, after almost a year’s worth of dead ends, they arrived at the impact hypothesis. On an otherwise ordinary day sixty-six million years ago, an asteroid six miles wide collided with the Earth. Exploding on contact, it released energy on the order of a hundred million megatons of TNT, or more than a million of the most powerful H-bombs ever tested. Debris, including iridium from the pulverized asteroid, spread around the globe. Day turned to night, and temperatures plunged. A mass extinction ensued. Even groups that survived, like mammals and lizards, suffered dramatic die-offs in the aftermath. Who perished, and who survived, set the stage for the next 66 million years—including our own origin 300,000 years ago.

The Alvarezes wrote up the results from Gubbio and Stevns Klint and sent them, along with their proposed explanation, to Science. “I can remember working very hard to make that paper just as solid as it could possibly be,” Walter later recalled. Their paper, Extraterrestrial Cause for the Cretaceous-Tertiary Extinction, was published in June 1980. It generated enormous excitement, much of it beyond the bounds of paleontology, but it was also ridiculed by some who considered the idea far-fetched, if not ridiculous. Journals in disciplines ranging from clinical psychology to herpetology reported on the Alvarezes’ findings, and soon the idea of an end-Cretaceous asteroid was picked up by magazines like Time and Newsweek. In an essay in The New York Review of Books, the late American paleontologist Stephen Jay Gould quipped that linking dinosaurs—long an object of fascination—to a major cosmic event was “like a scheme a clever publisher might devise to ensure high readership.”

Inspired by the impact hypothesis, a group of astrophysicists led by Carl Sagan decided to try to model the effects of an all-out war and came up with the concept of “nuclear winter,” which, in turn, generated its own wave of media coverage. But as the discovery sank in among many professional paleontologists, the Alvarezes’ idea—and in many cases, the Alvarezes themselves—were met with hostility. “The apparent mass extinction is an artifact of statistics and poor understanding of the taxonomy,” one paleontologist told The New York Times. “The arrogance.”

Skepticism was immediate and intense. Paleontologists, geologists, and physicists debated the implications of the iridium anomaly. But as the search for supporting evidence intensified, the pieces of the puzzle began to fall into place. Shocked quartz, a telltale sign of high-energy impacts, was found at sites around the world. Soot deposits suggested massive wildfires had raged in the aftermath.

Artists rendering of T-rex and other dinosaurs prior to the impact of the asteroid (Erik Olsen)

In the early 1990s, conclusive evidence finally emerged. The Chicxulub crater, measuring roughly 180 kilometers across and buried under about half a mile of sediment in Mexico’s Yucatán Peninsula, was identified as the likely impact site. Although it was first detected by Mexico’s state-run oil company (PEMEX) in the 1950s during geophysical surveys, core samples taken decades later clinched the identification of Chicxulub as the long-sought impact site linked to the mass extinction that ended the Cretaceous era.

One of the more intriguing (if not astounding) recent discoveries tied to the end-Cretaceous impact is a site called Tanis, located in North Dakota’s Hell Creek Formation. Discovered in 2019 by a team led by Robert DePalma and spotlighted in a New Yorker article, Tanis preserves a remarkable snapshot of what appears to be the immediate aftermath of the asteroid strike.

Tanis fossils (Image credit: Courtesy of Robert DePalma)

The sedimentary layers at Tanis indicate large waves—often called “seiche waves”—that may have surged inland in the immediate aftermath of the impact. They also contain countless tiny glass spherules that rained down after the explosion. Known as microtektites, these blobs form when molten rock is hurled into the atmosphere by an asteroid collision and solidifies as it falls back to Earth. The site appears to hold them by the millions. In some cases, fish fossils have been found with these glass droplets lodged in their gills—a striking testament to how suddenly life was disrupted.

Although still under investigation, Tanis has drawn attention for its exceptional level of detail, potentially capturing events that took place within mere hours of the impact. The precise interpretation of this site continues to spark controversy among researchers. There is also controversy about the broader cause of the mass extinction itself: the main competing hypothesis is that the colossal “Deccan” volcanic eruptions, in what would become India, spewed enough sulfur and carbon dioxide into the atmosphere to cause a dramatic climatic shift. However, the wave-like deposits, along with the abundant glass spherules, suggest a rapid and violent disturbance consistent with a massive asteroid strike. Researchers hope to learn more about the precise sequence of disasters that followed—tidal waves, intense firestorms, and global darkness—further fleshing out the story of how the world changed so drastically, so quickly.

Glass spherules from cosmic impacts—microtektites from Tanis, tiny relics of Earth’s violent encounters with space. (Image credit: Courtesy of Robert DePalma)

All said, today the Alvarez hypothesis is widely accepted as the leading explanation for the K-Pg mass extinction. Their contributions at UC Berkeley—widely recognized as one of the world’s preeminent public institutions—not only reshaped our understanding of Earth’s history but also changed how we perceive planetary hazards. The realization that cosmic collisions have shaped life’s trajectory has led to renewed interest in asteroid detection and planetary defense.

Walter and Luis Alvarez’s discovery was a testament to the power of interdisciplinary science and the willingness to follow unconventional ideas. Their pursuit of an extraterrestrial explanation for a terrestrial mystery reshaped paleontology, geology, and astrophysics. What began with a father and son pondering an ancient Italian rock layer ended in a revelation that forever changed how we understand the history of life—and its vulnerability to forces from beyond our world.

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