June 20, 2025 — As humanity grapples with the dual crises of global warming and mass species extinction, scientists are turning to some of the planet’s smallest yet most revealing witnesses: foraminifera. These single-celled marine organisms, encased in intricate shells of calcium carbonate, have left behind a fossil record so abundant and continuous that they offer one of the clearest windows into Earth’s climatic upheavals across hundreds of millions of years.
Unlike most species, whose fossils appear only sporadically, foraminifera — or “forams” for short — rain down in staggering numbers onto the ocean floor when they die, layering the seabed with an unbroken archive of environmental change. Each microscopic shell not only preserves the physical imprint of the organism but encodes chemical signatures of the ocean’s past temperatures and conditions.
“When you look at a living foram, it’s like a little grain of sand with a big sunburst of snotty tentacles around it,” quips paleoceanographer Chris Lowery of the University of Texas at Austin, describing the living forms that feed with elegant tentacle-like extensions.
For generations, paleontologists and climate scientists have used these humble fossils to piece together how marine life endured — or perished — through cataclysmic events: asteroid strikes, global ice ages, and ancient greenhouse spikes. Today, these same fossils may offer vital clues about how marine ecosystems could fare under rapid climate change driven by human activity.
Survivors and Victims of Catastrophe
Foraminifera first appeared around 180 million years ago during the Jurassic period and have since survived every major crisis that wiped out countless other species. Among their most telling chapters is the catastrophic asteroid impact 66 million years ago, which famously ended the age of the dinosaurs.
“Everyone talks about the dinosaurs going extinct at that time,” says micropaleontologist Paul Pearson of University College London. “But we know the details of what happened from foram fossils.”
Beneath the impact layer, rich beds of planktonic foraminifera abruptly thin out, revealing how nine out of ten planktonic species vanished after the asteroid’s fallout blocked sunlight for years, starving marine food webs. By contrast, deep-sea dwelling forams fared better, feeding on debris in the darkened oceans and riding out the extinction event.
Recovery, however, was painfully slow: as Fraass and Lowery reported in 2019, it took about 10 million years for foraminifera to regain their lost diversity. Yet mass die-offs also cleared ecological space for innovation. New foraminiferan species emerged, some sporting spines that may have helped them stay afloat and capture more food in the changed oceans.
Lessons From Ancient Warming
While the asteroid strike plunged Earth into darkness and cold, foraminifera also record the opposite crisis: episodes of sudden global warming eerily reminiscent of today’s man-made greenhouse effect.
One stark example occurred about 56 million years ago, when volcanic eruptions unleashed vast amounts of carbon dioxide, raising global temperatures by up to 5 degrees Celsius. Deep-sea foraminifera suffered badly as the ocean acidified, dissolving their calcareous shells. Yet planktonic species showed remarkable resilience by migrating into cooler waters, a survival strategy that modern marine species are beginning to mimic.
“In the tropics, it may have become too hot for them to survive, with water temperatures up to 40 degrees C,” explains marine ecologist Tracy Aze of the University of Plymouth. “We see tropical species show up in more temperate areas — while temperate species shifted polewards, as they are again doing today.”
When temperatures swung the other way around 34 million years ago — during the Eocene-Oligocene transition — dramatic cooling triggered another wave of extinctions among foraminifera. The lush variety of ornate planktonic forms vanished, replaced by smaller, plainer species adapted to the colder seas of the emerging ice ages.
A Fragile Future for the Ocean’s Timekeepers
Today, foraminifera remain sentinels of change. Scientists routinely drill deep into ocean sediments, retrieving tubes of mud that contain millions of fossilized forams stacked layer upon layer — a precise timeline stretching back eons. This natural archive has become vital for predicting how marine ecosystems may respond to the rapid warming of the 21st century.
A 2023 study led by Pearson showed that if global warming stays below 2 degrees Celsius, food supply in the ocean’s midwater “twilight zone” — a crucial region for marine life between 200 and 1,000 meters deep — may still shrink by over 20%. In a worst-case scenario with 6 degrees of warming, that decline could reach 70%, threatening species ranging from lanternfish to the great whales that feed on twilight zone prey.
Already, researchers observe modern parallels to ancient migrations: foraminifera are moving poleward as equatorial waters grow too hot, resulting in declining diversity at the tropics. Alarmingly, a 2024 study found that global foraminiferan abundance has dropped nearly 25% in just the past 80 years — a troubling sign for other species that rely on similar ecological conditions.
While forams have survived asteroid impacts, volcanic winters, and ice ages, the speed of current climate change — driven by humans — may test even their legendary resilience.
“Since foraminifera as a group bounced back from several mass extinctions, they’re very unlikely to disappear altogether,” says Fraass. “But recovery may take a long time, and humanity’s involvement makes predicting the near future especially difficult.”
As Lowery dryly concluded: “Ask me again in a couple thousand years.”