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  • Many scientists think we're now in the middle of a mass extinction event.

  • Is this true and will we survive?

  • First of all, let's define what a mass extinction event is.

  • It's a large die-off of species and it's only happened five or six times

  • in the 4 billion year history of life on this planet.

  • The most famous extinction event happened 65 million years ago

  • when an asteroid struck what's now the Yucatan Peninsula in Mexico.

  • The asteroid kicked up a lot of dust,

  • creating a shift in climate and wiping out the dinosaurs and many other species.

  • Of course, this event had a happy ending for us

  • because it killed off the big reptiles and created space for mammals

  • and ultimately, humans.

  • We may not be so lucky next time.

  • Mass extinction events can wipe out as many as 90 percent of all species.

  • Humans would most certainly not survive an event of that magnitude.

  • But there's no iron-clad proof that we're in a mass extinction event now.

  • The only thing we know about past extinction events

  • is what we see in the fossil record.

  • Even though today, we're losing, by some estimates, 200 species a day,

  • that still doesn't add up to what we know happened in the past.

  • The passenger pigeon is a case in point.

  • It once numbered in the billions in North America and is now extinct.

  • But there are only two known examples of this species in the fossil record.

  • What has scientists worried, though, is a similarity between what's happening now

  • and what we see in past extinction events.

  • For example, the Permian Extinction Event, about 250 million years ago,

  • was started by a massive volcanic eruption in what is now Siberia.

  • Lava vaporized a huge cold deposit, causing a spike in carbon emissions

  • on the order of what we're seeing today.

  • Another example is the Great Oxygenation Event of 2.4 billion years ago.

  • Here, cyanobacteria, a precursor to modern-day plants,

  • began emitting oxygen, gassing much of the anaerobic bacteria into oblivion.

  • We're currently changing Earth's atmospheric chemistry in similarly large ways.

  • Only time will tell if we're causing another mass extinction.

  • For Scientific American's Instant Egghead, I'm Fred Guterl.

Many scientists think we're now in the middle of a mass extinction event.

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第六次大量絶滅に直面している?- インスタントエッグヘッド#24 (Are We Facing the Sixth Mass Extinction? - Instant Egghead #24)

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    Kaku Tomish に公開 2021 年 01 月 14 日
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