Ancient Extinction

Why a 450-million-year-old event is worth paying attention to

At the beginning of the Late Ordovician, a geological period scientists date to roughly 455 million years ago, a great diversity of animal and plant species thrived in the warm, shallow seas that dominated the Earth’s surface. Ten million years later, at the Ordovician’s end, the vast majority were extinct. Getting to the bottom of what happened and why, according to MU climatologists Page Quinton and Kenneth MacLeod, could lead to a better understanding of climate change issues in our own time.

This much the fossil record clearly indicates, the researchers say. Around 450 million years ago, the Earth began to get colder, so cold, in fact, that a mass extinction ensued. Plummeting temperatures weren’t the only change at the advent of this ancient ice age; there was also a significant drop in carbon dioxide levels that may have caused cooling.

Exactly when and how CO2 levels might be implicated in the Ordovician die-off is the subject of a recent study by Quinton and MacLeod. Their findings suggest that episodes of increased plant growth and burial during the Ordovician could have shifted the balance of the “carbon cycle” — the process by which carbon is exchanged around our planet’s oceans, atmosphere, ecosystem, and geosphere — and lowered CO2 levels.

“Climate is not a simple science; many small factors determine what exactly leads to global warming and cooling trends,” says MacLeod, a prominent professor of geological sciences whose previous work on mass extinctions were detailed in Illumination’s Spring/Summer 2007 issue. “By understanding the deep past, we have better information about historic trends that lead to better predictions. Understanding carbon cycles adds value to our knowledge base of climate change.”

During the Late Ordovician period, most of North America was submerged beneath a warm sea. What is now Alabama was on the margin of that sea, a place where local environmental effects may have significantly affected carbon cycling. Quinton, a doctoral student in MU’s geological sciences program, led a field research team in the northeastern part of the state that collected rock samples from formations exposed when workers cut highways through the region’s hills. He then analyzed the samples for chemical clues that could be related to CO2 levels at specific time periods. “After examining rocks 450 million years old or older, we believe the drop was caused by a massive burial of organic carbon during the time period,” Quinton says. “We’re trying to determine whether or not there was an increase in plant productivity, think huge algae blooms, that died and fell to the sea floor, basically burying CO2. This burial, coupled with the mountain-building event that created the Appalachian Mountains, could have contributed to the resulting ice age.”

Quinton and MacLeod’s study, conducted with research collaborators Stephen Leslie of James Madison University and Achim Herrmann of LSU, was published earlier this year by the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

Ancient Extinction photo

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