By the time it ended, 75 percent of the world's marine organisms were extinct. But very slowly the planet began to warm, gradually eroding the mega-continent of ice around the South Pole, and many of the tiny creatures and plants that had died out were replaced by new organisms. Life began anew on planet Earth.
It happened, not because of a cataclysmic impact by a foreign body, like the one believed to have wiped out the dinosaurs. It happened simply because the planet's climate began to change, apparently fairly quickly, but not nearly as fast as the changes we are seeing today.
It's not particularly important that all of this happened around 440 million years ago. What's important is that the consequences were rapid, at least on a geological time scale, and they were nearly total.
For the first time scientists are able to measure how intense it all was.
"The big breakthrough here is the ability to tell how much of this climate change was felt by temperature change in the tropical oceans, and how big the ice sheets got," Woodward Fischer, assistant professor of geology at the California Institute of Technology, said in a telephone interview.
"We can really tell you how intense this glaciation was, and the thing that's so remarkable about it is there's a relatively large temperature change associated with it" of about 10 degrees Fahrenheit.
That change in average global temperature peaked near the end of what is known as the Late Ordovician period, and it coincided precisely with the second largest mass extinction in the history of the planet. The moral is pretty clear: Climate change can wreak havoc around the Earth, especially if the change happens relatively quickly.
For many years scientists have tried to figure out just what the global climate was like, but obviously 440 million years is a long time ago, and while fossils from that era have been found around the Earth the actual temperature seemed impossible to pin down. To do that, they needed to know how much water was locked up in long-gone ice sheets.
A team of nine scientists from five different institutions convened at Caltech to tackle the problem. Using a new "paleothermometer" developed at Caltech, they analyzed the isotopic chemistry of fossilized marine animal shells collected from Canada and the Midwestern United States. The new technique measures "clumpiness" of heavy isotopes in fossils. The lower the temperature, the clumpier the isotopes. That allowed them to determine the climate, and they thus could figure out the thickness of the ice.
It turns out that the ice cap at the South Pole would have dwarfed what is now Antarctica. It spanned across land masses that later drifted to the equatorial region and became Africa and South America.
"The sea level was probably as high as it's been in the last 500 million years," said Seth Finnegan, a postdoctoral researcher at Caltech and first author of a study published in the journal Science. "Most of the continents were extensively flooded with very shallow inland seas. We don't really have anything comparable to it in the world today. It was a rich habitat for marine life."