Ancient Rocks From China Offer Clues to Climate Change
Date: May 6, 2002
And Research Challenge for UC Geology Undergraduate
By: Chris Curran
Phone: (513) 556-1806
Photos by: Colleen Kelley
Archive: Research News
McMicken College of Arts and Sciences geologists studying rocks more than 700 million years old from southern China are hoping the rocks will reveal information about global climate change and a better understanding of an event called "Snowball I."
The work included an undergraduate research project by senior John Alten, who reported his results in the recent joint meeting of the North-Central and Southeastern Sections of the Geological Society of America meeting in Lexington, Kentucky.
Alten, working under the direction of Professor Barry Maynard, examined rocks collected by Maynard and former UC graduate student Tie-bing Liu. They cover the time period roughly 700-750 million years ago, well before there was extensive life on land.
Alten conducted a "whole rock" chemical analysis on the samples. One of the striking findings was a high concentration of unusual forms of sulfur, as determined by sulfur isotopes. "It definitely tells us that the Earth was different at this time, most likely with the oceans lacking oxygen," explained Maynard.
The time period being studied included two major glaciations and an event called "Snowball I."
Snowball Earth theory involves glaciations which lasted about 10 million years," explained Alten. "They lasted much longer than more recent glaciations and may have involved much of the
Earth's surface. The significance here is most land masses were lying at low latitudes near the equator at that time, unusual locations for glaciers by modern comparison."
The heavy sulfur isotopes found in the rock samples support the Snowball Earth hypothesis, because they indicate the oceans lacked oxygen during that time period.
"One way to get an oxygen-free ocean is to have it freeze over entirely, which has been proposed," said Maynard. "Once the ice melts, the deep ocean water that has been accumulating iron, manganese, and this peculiar sulfur gets stirred up (the deep-water overturn) and comes onto the shallow shelf where these sediments we are studying get deposited."
The samples were taken from two manganese mines, Tanganshan and Xiangtan in Hunan Province. Although Alten did not personally collect the samples, he said he was grateful for the opportunity to be involved with their analysis.
"Presenting at a professional conference as an undergraduate was a rich
experience for me, because I was surrounded by a genuinely interested
population and exposed to new ideas and information.
And even though Alten recognizes the practical benefits of developing marketable skills and applying what he's learned in the classroom to an actual research project, he said the ultimate
benefit is an intangible one.
"Sometimes it's just the thrill of knowing more that provides the reward."