Selects: How Extinction Works

Key Takeaways

Extinction, a natural process, is now occurring at rates 100 to 1,000 times higher than historical averages.
Early scientific views of extinction evolved from preclusion to gradual disappearance, then catastrophic events.
The fossil record is incomplete, making species counts and confirmed extinctions challenging to determine.
Human activities are identified as primary drivers of current species loss through habitat changes and climate impacts.
Five major mass extinction events have significantly reshaped Earth's ecosystems over geological time.
The current rapid loss of species is debated as a sixth mass extinction, driven by human environmental changes.
Ocean acidification, a consequence of increased atmospheric CO2, poses a severe threat to marine life.
Some species, like the coelacanth, have been rediscovered after long periods, challenging extinction definitions.

The episode introduces extinction using Elizabeth Kolbert's book 'The Sixth Extinction' and a New Yorker article as primary sources.
Historically, scientific belief precluded extinction, assuming God's perfect creation meant no species would disappear.
In 1812, George Cuvier proposed species could go extinct, hypothesizing cataclysmic events caused these disappearances.
Thomas Jefferson, in the 19th century, believed the Great Mastodon might still exist in the American West.

For decades, Darwin's influence led to the dominant scientific view that extinction was a slow, gradual process, persisting until the 1990s.
The understanding of mass extinctions shifted in 1991 with the widely accepted Alvarez hypothesis.
This hypothesis proposed a large asteroid impact 65 million years ago caused the extinction event that wiped out dinosaurs.
The impact crater, 112 miles wide, was discovered under the Yucatan Peninsula and dated to the dinosaur extinction, marking the end of the Cretaceous period.

Current extinction rates are estimated to be 100 to 1,000 times higher than the historical background rate.
The ongoing mass extinction lacks a clear endpoint or period of recovery, posing a unique danger from continuous human-caused environmental changes.
While intellectually viewed as transformative, leading to new evolutionary opportunities, humans are significantly contributing to this potential sixth mass extinction.
Scientists debate whether the current human-caused extinction event should define a new geological epoch, the 'Anthropocene.'

Studying extinction rates is challenging due to the incomplete nature of the fossil record, making exact species counts difficult.
The absence of fossil evidence does not confirm extinction, as specific conditions are needed for fossil formation.
Scientists use mathematical models and algorithms to estimate species populations and extinction events, defining concepts like minimum viable population.
Species like the coelacanth, a 'Lazarus species,' were rediscovered in the 1930s after being thought extinct for over 400 million years.

Extinction is a natural process, but humans significantly contribute through habitat changes, competition, and environmental contamination.
The stellar sea cow, described in 1741, went extinct by 1768, illustrating rapid human-induced species loss.
The loss of a single species, such as bees, can trigger a domino effect throughout an ecosystem, impacting pollination and other animals.
De-extinction efforts, like the brief 2003 revival of the Spanish mountain goat (Bucardo) using frozen DNA, raise ethical questions about resource allocation versus protecting existing species.

The Ordovician extinction, approximately 490 million years ago, eliminated roughly half of all marine animal families due to falling sea levels.
The Permian-Triassic extinction, 'The Great Dying' 250 million years ago, was the most severe, wiping out up to 96% of all life, possibly from volcanic activity.
The end-Triassic extinction 200 million years ago caused the loss of 20% of marine families and half of marine genera.
The Cretaceous-Paleogene (K-Pg) event 65 million years ago, attributed to an asteroid impact, caused widespread devastation and dinosaur extinction.

The 'overkill hypothesis' suggests human expansion into regions like Australia 50,000 years ago and North America 11,000 years ago coincided with megafauna extinction.
Some scientists question if early human population sizes were sufficient for overhunting to be the sole cause of widespread megafauna loss.
Alternative theories attribute extinctions to natural climate change, with some suggesting human-caused climate change is also a factor.
A global analysis found 177 large mammal species disappeared between 132,000 and 1,000 years ago, primarily during periods of human expansion.

Scientists largely agree the Earth is experiencing a rapid mass extinction, with one-third of coral reefs and amphibians, one-quarter of mammals, and one-eighth of birds currently threatened.
Human expansion, farming, logging, and altered waterways are identified as primary drivers; for example, only 2% of U.S. rivers remain unimpeded.
Ocean acidification from increased atmospheric carbon dioxide, described as 'global warming's evil twin,' has dramatically dropped ocean pH over 50 years.
Rediscovered species include the Bermuda Petrel, found in 1951 after being thought extinct since the 1600s, and the Cuban solenodon, rediscovered in 2003.