But as the ice sheet at the South Pole grew, it sucked water out of those seas, drying the habitat and killing its inhabitants. The world became a very cold, and largely lifeless, place.
Scientists want to learn how all that happened because it may help us understand "the potential climate change we may be headed into," Finnegan said. It's important "to understand how the global biota seems to respond to different changes in the climate system through time."
Yet the world, and its atmosphere, and even the sun were quite different during the Late Ordovician period. Even opposites, in some ways. Scientists have estimated that the earth's atmosphere at that time contained up to 16 times the amount of carbon dioxide that it does today.
Today, the concern is that the amount of carbon dioxide is growing, causing a greenhouse effect that will warm the planet for the next few centuries. So why was the earth a big snowball way back when the atmosphere was much richer with carbon dioxide? The answer shows just how remarkable our planet is.
"As you go back in time, our sun was actually dimmer, and it's getting brighter with time," Fischer said. "The earth has kind of a built in thermostat that sets the carbon dioxide level at what it needs to provide the climate conditions" suitable for life. "That means liquid water on the surface of the earth."
So as the sun brightened over time, carbon dioxide was absorbed by rocks and plants ranging from algae to, eventually, forests, keeping the climate from getting too hot. But that cuts both ways. Some scientists have speculated that a sudden drop in carbon dioxide could have caused the earth to turn bitterly cold in the so-called "snowball earth" periods of glaciation that led to ice ages of varying intensities.
So too little carbon dioxide and the earth turns cold, too much and it turns hot, sustaining life most of the time, but occasionally destroying habitats and all those who depend on them.
That's essentially what this seemingly arcane research is all about.
"When you look back in time you realize that extinction of species has been highly non-random," Finnegan said. "There have been times when many, many have gone all at once, and it's hard not to wonder why that is."
"We are looking at a mass extinction, and there's always the question of how flexible, how plastic, is the biology," Fischer added. "Is there time to adapt?
"We are looking at a time when the climate change was rapid, at least on the geologic time scale we can measure, but it still may not have been anything near the pace that we see in climate change today. None the less, the biology felt this climate change" 440 million years ago.
Far from the polar ice sheet, in a relatively warm area near the equator, the temperature plunged several degrees. That may have taken several hundred thousand years, but it was enough to wipe out most marine organisms.
We're not heading for another snowball earth. But wherever we're going, it isn't going to take several hundred thousand years. And if a faster pace means greater impact, the consequences of the current warming trend could be severe.