14 DAY TRIAL // A research done at Ohio State University has found that the uplift of the Appalachian Mountains might have caused an Ice Age approximately 450 million years ago, during the Ordovician Period. Climate change associated with the mountain rising led to a sucking of carbon dioxide (CO2) from the atmosphere, causing a cooling effect on the weather.
Even the current ice age, which backs its roots 40 million years ago, is thought to have been caused by the rise of the Himalayas. This finding supports the idea that CO2 level in the atmosphere is the main actor in Earth's climate. We are currently living in a slightly warmer interglacial period within an Ice Age, when CO2 levels in atmosphere must be low; but burning fossil fuels by humans have raised CO2 levels, which could reverse the climate.
The planet has passed through glaciation several times during its history and carbon dioxide might have always been the main responsible. "In this study, we're seeing remarkable evidence that suggests atmospheric CO2 levels were in fact dropping at the same time that the planet was getting colder. So this significantly reinforces the idea that CO2 is a major driver of climate," said Matthew Saltzman, professor of geological sciences
Ordovician quartz sandstone deposits from Nevada and two sites in Europe have been analyzed, comparing the proportion of two isotopes of the element strontium, Sr 87 and Sr 86. Immediately prior to the Ordovician Ice Age, the strontium ratio decreased dramatically. A vast amount of volcanic rock must have been eroded and carried away by the waters to the bottom of the oceans. "We observed a major shift in the geochemical record, which tells us something must have changed in the oceans," Young said.
The strontium ratio decline fits the uplift of the Appalachian Mountains. The mountains appeared as the crustal plate underneath which now the Atlantic is pushed against the eastern North America.
The phenomenon was associated with the emergence of ancient volcanic rock up from the seafloor and onto the continent. "This kind of silicate rock weathers quickly, explained Seth Young, a doctoral student in earth sciences. It reacts with CO2 and water, and the rock disintegrates. Carbon from the CO2 is trapped in the resulting sediment."
The chemical reaction sucked large quantities of CO2 from the atmosphere at the beginning of the Ordovician Ice Age. Ordovician, initially a warm period, ended with glaciers covering the poles and mountains' top. The climate shift produced by the emergence of the Appalachians took place in only 7 - 8 million years, a very short geological time.
The glaciation was accompanied by mass extinctions in the ecosystems. "We are seeing a mechanism that changed a greenhouse state to an icehouse state, and it's linked to the weathering of these unique volcanic rocks," Young said.
The volcanic rock responsible for decreasing CO2 amount is called also "island arc" rock, because it is common in curved volcanic archipelagos like Indonesia and Japan. "Those rocks are around today, where you have ocean crust being subducted under a crustal plate," Young explained.
"What's unusual about the Ordovician period is that those island arcs were being uplifted onto a continent. The ones in the Pacific Ocean now are mostly underwater, so they're not weathering away like the Appalachian rock did."
"In the Himalayas, the process would have been the same -- silicate rocks are exposed to the atmosphere, weathering sucks CO2 out of the atmosphere and chills the planet," Saltzman said.
"This may be the only effective way to bring CO2 levels down to a threshold that's cool enough for ice to start building up."