Homo Sap, as a species, has only existed for about 200,000 years. As a civilized species, socalled, for only about 10,000 years, and with 7 billion members at the same time, never before. And we depend on an agriculture that depends on the weather. Weather that is already getting real dicey because of the effects of a rapidly warming earth.
Not only that, but in that 4.5 billion years, there have been several periods of mass extinction, and most of them have involved major changes in the GHGs in the atmosphere.
Did Greenhouse Gases Unleash the Dinosaurs Science AAAS News
Linking eruptions to evolution has taken some detective work. The mass extinction 201 million years ago at the end of the Triassic period (known as the end-Triassic extinction) wiped out half the known species on land and in the sea, paleontologists found, which triggered the rise of the dinosaurs. When the extinction nearly wiped out the early relatives of the crocodiles, it removed the biggest competitors of early dinosaurs and let them rise to dominance.
More recently, researchers dating both that extinction and massive volcanic eruptions around then have found that the two major evolutionary and geologic events occurred at the same time. The massive outpourings of lava now strewn along the edges of the North Atlantic Ocean were laid down at the very start of the mass extinction, geochronologists have found. The coincidence is so close—a geologic moment of a few tens of thousands of years or so—that the eruptions and the mass extinction appear to have been connected.
To find out how eruptions—however massive—could cause global extinctions, paleoecologist Micha Ruhl of Utrecht University in the Netherlands and his colleagues went to the fossil record—the very small-scale fossil record. As they report online today in
Science, they extracted distinctive organic molecules from marine sediments in Austria. The molecular chains, each 23 to 35 carbon atoms long, had been part of plant waxes washed off the land. The proportion of two isotopes of the carbon in the former plant waxes changed dramatically right at the end of the Triassic. That ratio shift depended on the amount of carbon dioxide used by the plants from different sources: carbon dioxide from the eruptions or methane (later converted to carbon dioxide) locked in ice in the sea floor. The group found that at least
12 trillion tons of carbon in the form of carbon dioxide or methane—two greenhouse gases—had gushed into the atmosphere during just 10,000 to 20,000 years.
Worst Mass Extinction Ever Took Only 60 000 Years - Scientific American
It took only 60,000 years to kill more than 90 percent of all life on Earth, according to the most precise study yet of the Permian mass extinction, the greatest die-off in the past 540 million years.
The new timeline doesn't reveal the culprit behind the die-off, though scientists have several suspects, such as volcanic eruptions in Siberia that belched massive quantities of climate-changing gases. But pinning down the duration of the
Permian mass extinctionwill help researchers refine its potential trigger mechanisms, said Seth Burgess, lead study author and a geochemist at MIT.