Acid rain -- rich in carbon dioxide -- pelted the newly exposed Appalachian rock and wore it away. Chemical reactions trapped the carbon in the resulting sediment, which formed reefs in the vast seas that covered North America.
For about 10 million years, the volcanoes continued to add carbon to the atmosphere as the Appalachians removed it, so the hothouse conditions remained stable. Life flourished in the warm oceans, including abundant species of trilobites and brachiopods.
Then, 450 million years ago, the eruptions stopped. But the Appalachians continued weathering, and atmospheric carbon levels plummeted. The Earth swung from a hothouse to an icehouse.
By 445 million years ago, glaciers had covered the south pole on top of the supercontinent of Gondwana (which would eventually break apart to form the continents of the southern hemisphere). Two-thirds of all species had perished.
When they started this research, Saltzman and his team knew that Earth's climate must have changed drastically at the end of the Ordovician. But they didn't know for certain that volcanoes were the driving force, explained Seth Young, who did this research for his doctoral degree at Ohio State. He is now a postdoctoral researcher at Indiana University.
"This was not necessarily what we expected when we started investigating, but as we combined our data sources, the story began to fall into place," Young said.
Using a computer model, they drew together measurements of isotopes of chemical elements -- including strontium from rocks in Nevada and neodymium from rocks in Virginia and Pennsylvania -- with measurements of volcanic ash beds in the same locations. Then they factored in temperature models developed by other researchers.<
|Contact: Matthew Saltzman|
Ohio State University