The science behind extinction

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A collection of research and insights from Stanford experts who are deciphering the mysteries and mechanisms of extinction and survival in Earth’s deep past and painting an increasingly detailed picture of life now at the brink.

An estimated 8 million animal and plant species live on planet Earth.  But extinction rates are  accelerating. Gorillas, gazelles, frogs, rhinos and whales are among the species now critically endangered, and human activities present the biggest threat. 

In mass extinctions, a huge portion of the planet’s species die off over thousands or even millions of years - a geological blink. Scientists have identified five of these events in fossil data going back roughly half a billion years. 

Scientists who study past extinction events can find clues about not only the evolution of life on Earth, but also about the effects of extreme changes in our planet’s atmosphere, and how life finds ways to rebound. Stanford scientists and colleagues have uncovered evidence, for example, that the biggest extinction in Earth’s history  was caused by global warming that left ocean animals unable to breath.

Other research, coauthored by Stanford geophysicist Sonia Tikoo-Schantz, suggests the crater from the giant asteroid impact linked to the dinosaur extinction some 66 million years ago may have  provided niches for life.

"The fossil record is our only archive of past extinction events," Stanford paleobiologist Jonathan Payne has said. It allows researchers to examine directly which biological traits tend to lead to higher extinction risk under different circumstances, whether in the wake of an asteroid impact or volcanic eruption, or amid global warming. 

Many scientists say a sixth mass extinction is now under way. In 2019, following a review of thousands of scientific and government sources, the United Nations’ Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services  reported that approximately 1 million animal and plant species are threatened with extinction. According to the report, more than 40 percent of amphibian species, nearly 33 percent of sharks, shark relatives and reef-forming corals, and upwards of 33 percent of all marine mammals are threatened. 

Even parasites are under threat. Up to one-third of the world’s parasite species could  go extinct within a few decades - potentially opening new niches for other, invasive parasites to exploit. And losses can snowball. As Stanford biologist Paul Ehrlich and colleagues wrote in a recent study suggesting the extinction rate is likely much higher than previously thought, " Extinction breeds extinction."

When species vanish, benefits to humanity can be lost, too - from economic opportunities related to ecotourism to keeping in check populations of species that can spread infectious disease. The UN report estimated that as much as $577 billion in annual global crops are now at risk from loss of pollinators. The consequences do not fall equally across society. The areas projected to see some of the worst negative effects from biodiversity loss and related changes to ecosystem functions are also home to many of the globe’s poorest communities as well as large concentrations of Indigenous peoples.

This collection covers how scientists are deciphering the mysteries and mechanisms of extinction and survival in Earth’s deep past and painting an increasingly detailed picture of life now at the brink. 

Scroll down for extinction research news and insights spanning  the future of our own species ; the disappearance of our hominid relatives and why the Neanderthals’ fate  could have been ours ; expanding knowledge of  past extinctions ; the root causes and ripple effects of the Earth’s ongoing  biodiversity crisis ; and connections between extinctions and pandemics.

Stanford epidemiologist Stephen Luby sees three potential outcomes for humanity by 2100: extinction, the collapse of civilization with limited survival, or a thriving society.

Teaching students about the existential threat of a pandemic as they are living through one can help make the danger feel less hypothetical and much more real.

Complex disease transmission patterns could explain why it took tens of thousands of years after first contact for our ancestors to replace Neanderthals throughout Europe and Asia.

November 2017

Humans didn’t outsmart the Neanderthals. We just outlasted them.

"It’s not that Neanderthals were these brutish, wide-shouldered, sort of advanced apes that roamed the land until we came over and beat them," Stanford evolutionary biologist Oren Kolodny tells The Washington Post. "It’s more that it was a companion hominin species that was very similar to us." September 2019

Earth has survived extinctions before, it’s humans who are fragile

A new scientific study co-led by Malcom Hodgskiss, a PhD candidate in Geological Sciences at Stanford, and "actual events reminded us this week that the Earth endures. It’s us, all the living things that inhabit it for a while, who are fragile; and who know our time is fleeting," says NPR Weekend Edition Saturday host Scott Simon.

Scientists have debated until now what made Earth’s oceans so inhospitable to life that some 96 percent of marine species died off at the end of the Permian period. New research shows the "Great Dying" was caused by global warming that left ocean animals unable to breathe.

In some ways, the planet’s worst mass extinction - 250 million years ago, at the end of the Permian Period - may parallel climate change today, according to research co-authored by Stanford scientists Jonathan Payne and Erik Sperling.

"Among the slew of Very Bad Things implicated in the worst calamity the Earth has ever known, it was the global-warming-driven ocean anoxia that stands out as the primary agent of Armageddon. And in this reaper of the Paleozoic," study authors including Jonathan Payne and Erik Sperling, "see a future menace."

February 2020

Body size and survival in the deep past

Fossil research suggests evolutionary winners during most of the history of animal life included not only true behemoths of the sea, such as Jurassic fish as long as a bus, but also species who were giants of their kind. April 2020

Study links ocean deoxygenation to ancient die-off

Researchers present new evidence that the deoxygenation of the ocean wiped out biodiversity during one Earth’s "Big Five" mass extinctions. Today, climate change contributes to decreasing oxygen in the oceans.

When significant oxygen entered the atmosphere, ancient life multiplied. But after a few hundred million years, Earth’s oxygen plummeted, resulting in a die-off likely greater than the extinction of the dinosaurs.

The most catastrophic wipe-out on Earth didn’t happen to the dinosaurs. A study co-led by Malcom Hodgskiss, a PhD candidate in Geological Sciences at Stanford, found extreme changes in the atmosphere killed almost 100 percent of life on Earth about 2 billion years ago.

Upending an evolutionary theory proposed in the 1950s, scientists have found that the groups most resistant to extinction also contain the greatest ecological diversity - their members perform a larger number of different functions in ecosystems.

Scientists have long associated larger brain size with a cognitive ability to adapt to difficult scenarios, but new research suggests that mammals with relatively larger brains might be at a higher risk of extinction.

Paleoecologists Anthony Barnosky and Elizabeth Hadly warn in their book, "Tipping Point for Planet Earth: How Close Are We to the Edge’," that "changes on Earth are aggregating in a way and at a speed that indicate a planetary tipping point is just ahead. The primary driver is overpopulation and attendant overconsumption of resources."

Research co-authored by Luke Frishkoff, Gretchen Daily and Elizabeth Hadly shows the effects of deforestation and climate change are amplified in a way that pushes particularly vulnerable rainforest species towards extinction, while dry-climate species persist.

November 2016

’Flattening out diversity’

"When we lose the big ones we lose their interactions with species lower down on the food chain, which causes more extinctions," Stanford paleoecologist Elizabeth Hadly tells Bay Nature magazine. "We’re going backwards along the evolution of life, eliminating the more complex animals and ending up with weedy species, generalists, slime." March 2017

To save the future, conservationists look to the past

Stanford professor Elizabeth Hadly and colleagues say the fossil record holds key insights into how a species or ecosystem might respond to changing conditions, and therefore might help guide more effective management efforts.

What will the world look like as iconic wild animals such as rhinos and tigers go extinct? Among other impacts: diminished biological diversity, fewer ecotourism job opportunities and the loss of benefits science is only beginning to discover, according to a call to action issued by a team of international scientists, including Stanford biologist Rodolfo Dirzo.

In today’s oceans, larger-bodied marine animals are more likely to become extinct than smaller creatures, according to a Stanford-led report. It’s a pattern that is unprecedented in the history of life on Earth, and one that is likely driven by human fishing.

An international study co-authored by Cassandra Brooks , PhD ’17, has debunked the popular view that Antarctica and the Southern Ocean are in a much better environmental shape than the rest of the world.

July 2017

’Biological annihilation’

"All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life," scientists Gerardo Ceballos, Paul Ehrlich and Rodolfo Dirzo write in Proceedings of the National Academy of Sciences. "Dwindling population sizes and range shrinkages amount to a massive anthropogenic erosion of biodiversity and of the ecosystem services essential to civilization."

Fossil study finds early human activity - not climate shifts - led to the systematic decline of large animals around the globe that predated human migration out of Africa. The findings add to concerns about continued biodiversity loss and the impact on ecosystems.

Stanford researchers show how warmer winters and booming demand for one of the world’s most expensive medicinal species may hurt ecosystems and communities in the Himalayas.

North America’s birds are disappearing from the skies at a rate that’s shocking even to ornithologists. Yet Stanford ecologist Paul Ehrlich sees some hope in this new jolt of bad news: "It might stir needed action in light of the public interest in our feathered friends."

The devastation of the vast majority of the world’s marine life is much closer than we think. According to Stanford paleobiologist Jonathan Payne, a scenario where all the ocean’s fish, mammals, and other creatures - even tiny animals like krill - are all gone is far from science fiction.

Analysis of thousands of vertebrate species reveals that extinction rates are likely much faster than previously thought. The researchers call for immediate global action, such as a ban on the wildlife trade, to slow the sixth mass extinction.

As humans diminish biodiversity, they’re increasing the risk of disease pandemics such as COVID-19. While some species are going extinct, those that tend to survive and thrive are more likely to host potentially dangerous pathogens that can make the jump to humans.

Stanford News Service

Biodiversity research at Stanford

Josie Garthwaite

School of Earth, Energy & Environmental Sciences
(650) 497-0947;  josieg@stanford.edu

The pandemic has tugged carbon emissions down, temporarily. But levels of the powerful heat-trapping gas methane continue to climb, dragging the world further away from a path that skirts the worst effects of global warming.

A new multi-drone imaging system was put to the test in Antarctica. The task? Documenting a colony of roughly 1 million Adélie penguins.

Researchers have developed a deep-learning model that maps fuel moisture levels in fine detail across 12 western states, opening a door for better fire predictions.

Unusual lightning strikes sparked the massive wildfires burning across California. Stanford climate and wildfire experts discuss extreme weather’s role in current and future wildfires, as well as ways to combat the trend toward bigger, more intense conflagrations.


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