The new findings mesh well with what scientists know about these ancient proto-Atlantic volcanoes, which are thought to have produced the largest eruptions in Earth's history. They issued enough lava to form the Appalachians, enough ash to cover the far ends of the earth, and enough carbon to heat the globe. Atmospheric carbon levels grew 20 times higher than they are today.
This study shows that when those volcanoes stopped erupting, carbon levels dropped, and the climate swung dramatically back to cold. The timing coincides with today's best estimates of temperature fluctuations in the Ordovician.
"The ash beds start building up at the same time the Appalachian weathering begins, but then the record of volcanism ends, and the temperature drops," Saltzman said. "Knowing these details can help us understand how carbon in the atmosphere is changing Earth's climate today."
Next, the researchers will examine the role of the ancient volcanic ash more closely. While the ash was in the atmosphere -- before it settled around the globe -- it might have blotted out the sun, and cooled the earth somewhat. Saltzman and his team want to make some estimate of this short-term cooling effect to refine their computer model.
Meanwhile, Young is just starting to re-analyze the same rock samples, this time looking for a different isotope -- sulfur. This, he hopes, will offer clues to how much oxygen was in the oceans, and how that oxygen may have affected life in the Ordovician.
|Contact: Matthew Saltzman|
Ohio State University