Mass Extinction
The extinction of a species or even whole families of animals and plants is so normal in Earth’s history. But it is not as bad as it sounds. The death knell of some species and the rapid rise of others is the reason so many kinds of life have been able to evolve.
There have been five or six in Earth’s history when the extinction clock has struck a particularly dark hour - marking the greatest mass extinction events.
Let’s start~!
First! Oxygen Holocaust (~2.5 to 2.2 billion years ago)
The first life-forms to rule the Earth were microbes that lived in an oxygen-free world. Oxygen, it turned out, was deadly poison to these ‘anaerobes.’ So when evolution spawned oxygen-gas-spewing microbes, the anaerobes were in big trouble. Earth was changed forever by this, the first major extinction event. But without it, oxygen-breathing animal life could not have evolved.
Second! Late Ordovician (~445 million years ago)
This event is perhaps the third largest mass extinction on record it terms of the general lost: 57 percent in all. At least two major extinction events appear to have piggybacked in this case. Most living creatures inhabited the sea at this time. Of the ones that left fossils, approximately 50 percent hit a dead end. The cause of all these losses might have been a drop in sea level spurred by plate tectonics. All that ice locked up on land would have dramatically lowered the sea levels worldwide, making things tough for shallow marine life - which comprised the majority of life on Earth at this time.
Third! Late Devonian (~370 million years ago)
Scientists believe that several deadly pulses blended together over time to create this mass extinction event. About half of genera known in the fossil record were extinguished, including many reef-building corals and other shallow marine organisms. The marine die-offs suggest that fluctuating sea levels may have played havoc with coastal habitats. Possible co-conspirators were land plants, which invaded and greened the continents and removed more carbon dioxide (a greenhouse gas) from the atmosphere. This might have led to global cooling, with more and larger glaciers pulling water from the world’s oceans.
Fourth! End Permian (~250 million years ago)
This was the most extinction event. It was the closest life has ever come to ending on Earth. A whopping 83 percent of all genera on land and sea went extinct at this time, including 96 percent of all marine species and 70 percent of all land vertebrates. A mass extinction of this magnitude liked had many interlinked causes. Among those we know about is the eruption of the colossal Siberian Traps, which probably jolted the Earth’s climate. Another player was the Supercontinent Pangea, which was just taking shape and altering ocean currents to create some stark temperature extremes between the equator and the poles.
Fifth! End Triassic (~200 million years ago)
As with the vastest majority of mass extinction events, the details of this one are largely a mystery. About one-fifth of all families of marine life were wiped out, which comes to about 48 percent of all genera, including ammonites, many reef-building corals, conodonts and seed ferns. The mostly like cause of all this activity was the eruption of the Central Atlantic magmatic province. Not only were more than 2 million cubic kilometers of lava spewed out over a period of many centuries, but more than 2 quadrillion kilograms of sun blocking sulfur was released, along with about twice as much climate-warming carbon dioxide. The result was probably a deadly climate roller coaster.
Sixth! End Cretaceous (~65 million years ago)
If you know of only one mass extinction event, it is probably this one. It is the most famous mass extinction event of them all, though not the biggest. It was the end of the great ‘age of reptiles’ - the demise of all but a small line of dinosaurs, which evolved into today’s birds. But a lot more than dinosaurs went extinct. This event saw the end of 17 percent of all families of living things, which translates into 50 percent of genera found in the fossil records at that time. Although the most popular theory is that an asteroid impact caused this mass extinction event, some researchers suspect it may not have been so simple or so sudden.
Last! Humanity’s Close Call (~73,000 years ago)
This event may have been a major squeaker for Homo sapiens: the titanic eruption of the Toba super volcano on the island of Sumatra. Some researchers think this caldera explosion caused global disruptions to ecosystems, reducing humanity to a few pockets of people - perhaps 10,000 individuals in all. Though this is not considered one of the ‘big five’ mass extinction events, it was almost our ‘big one’ and underscores the power of nature to wipe out species with little notice.
