Over 99% of the animal species that have ever
lived are now extinct. And sometimes, an event occurs causing changes so drastic that most
species are completely wiped out within a short period of time. So here are the 5 most
incredible mass extinctions ever to occur, and a look at whether the 6th might be happening
right now. 440 million years ago was the The Ordovician
extinction. At that time, most creatures swam or crawled in shallow seas. As newly created
volcanic rock was worn down by water and wind, it reacted with CO2 and absorbed it. As a result, carbon
dioxide levels dropped, temperatures fell and water got locked away as ice. This caused
ocean levels to drop and shallow seas to drain and after several cycles of growing and shrinking
glaciers, about 86 per cent of species were lost forever. Then over millions of years the oceans slowly
repopulated with fish and the land was colonized by early plants. These plants were then eaten
by the first crawling and flying insects. Then 374 million years ago these new plants
contributed to the next mass extinction. The plants absorbed enough C02 to create another
round of global cooling. They changed soil causing nutrients to wash into the ocean creating
enormous amounts of algae which sucked up oxygen. More than half of ocean species essentially
choked to death. Although somewhere in the world, a small family of fish with foot-like
fins and lungs managed to scrape by. Over the next 100 million years, these creatures would evolve into amphibians, reptiles and nearly all modern land animals. 250 million years ago is the Permian extinction.
The single worst mass extinction in history, 70 per cent of life on land and over 95 per
cent of life in the oceans was wiped out. Billions of tonnes of volcanic gases destroyed
the ozone layer and the average ocean temperature hit 40 degrees celsius, which is hotter than
most hot tubs. Acid rain fell all over the planet, devastating life on land. Life had only 50 million years to recover
until the fourth mass extinction came. At this time early small dinosaurs roamed the
land. A huge volcanic rift opened in the middle of the planet; eventually splitting
the Americas from Europe and Africa, and forming the Atlantic Ocean. The volcanoes spewed out
CO2, increasing temperatures and killing about 80 per cent of the species around at the time.
Yet in this newly emptied world dinosaurs did extremely well and during the next 135
million years, they grew to become some of the largest land animals the world had ever
seen. But all good things must come to the end. Many scientists believe that the extinction of dinosaurs was caused by an asteroid the
size of a small town crashing into what is now Mexico’s Yucatan peninsula. The impact
shot millions of tons of dust into the atmosphere, blocking out sunlight and spelling an end
to all large dinosaurs. The small ones that survived evolved into birds. The world was
now primed for a small, scuffling, rat-like creature, the ancestor of all modern mammals.
Within 50 million years, its descendants – from wildebeest and whales to horses and us humans
– have diversified and grown to dominate nearly every available environment on earth. So where does that leave us now, 65 million
years later? Well, human dominance of earth has led to big changes too, except the changes
of today are happening over decades, not millennia. Carbon dioxide levels, implicated in so many
of the past extinctions, have climbed at least 25 percent in just the last 50 years, almost
no time in geological terms. In addition to climate change, we’ve exterminated hundreds
of species by hunting, fishing, habitat destruction and pollution. It’s been estimated that
current species extinction rates are between 100 and 1000 times higher than the natural
background rate, and that if all the species that are currently threatened by declining
populations actually do go extinct, we may reach the level of a true mass extinction
in just a few hundred years. And while all the mass extinctions of the past have had
some survivors, it’s worth remembering that the creatures at the top of the food chain
are usually hit the hardest. We may be setting the stage for history to repeat itself, and
for some small, unexpected organism to replace us as the planet’s dominant form of life. Curious about the coolest animals that existed
during these mass extinctions? Check out our new video “5 Insane Creatures We Wish Still
Existed” over on our AsapTHOUGHT channel which explores some of the neatest and most
absurd creatures through history that are no longer with us. There’s a Link in the description
for that video. And subscribe for more weekly science videos! Video source: https://www.youtube.com/watch?v=wissIOikrqc
