Evidence uncovered that sheds light on Earth's origins
Posted: May 21, 2001

  Earth and Moon
Earth and Moon. Photo: NASA/GSFC
A Saint Louis University researcher has made a discovery near the Great Wall in China that could change the science of plate tectonics and provide some clues into how life might have developed on Earth.

The research, a collaborative effort involving Peking University and Washington University in St. Louis researchers, was published as a report in the May 11, 2001 issue of Science magazine.

It has been widely held that plate tectonics, or the motion of plates and continents, dates back 1.9 billion years. Timothy Kusky, Ph.D., professor of geology at St. Louis University, is part of a group of geologists who believe the plates began moving much sooner.

Kusky now believes he has the data to prove the theory. Last summer, he discovered the oldest complete section of oceanic sea floor on the planet, which is more than 500 million years older than previously documented. When he returned, he sought the assistance of Robert Tucker, Ph.D., associate professor of earth and planetary science at Washington University in St. Louis, to date the rare samples.

According to Tucker, the rocks are 2.5 billion years old and date back to Earth's earliest geologic time period, known as the Archean. The rocks are remarkably similar to much younger volcanic rocks that erupted on the sea floor in the process of sea floor spreading. For decades, geologists have debated whether plate tectonics operated in the Archean period. Those who have argued against that theory have cited the lack of any Archean ophiolites as their main line of evidence that plate tectonics did not occur on the early Earth. Ophiolites are rock structures formed on the sea floor when continents collide.

"This discovery shows that the plate tectonic forces that create oceanic crust on the Earth today were in operation more than 2.5 billion years ago," Kusky said.

Kusky said the findings could have a more far-reaching effect on theories related to the development of life on the planet. Scientists believe life on Earth during the Archean period consisted mainly of single-celled organisms in the oceans. Just when they evolved into more complex organisms has been contested for years.

"Because hot volcanic vents on the sea floor may have provided the nutrients and temperatures needed for life to flourish and develop, it's possible that life developed and diversified around these vents as plate tectonics began," Kusky said.

Kusky and Dr. Jiang-Hai Li of Peking University in Beijing made the discovery in a mountain belt in the Eastern Hebei Province, which is located only a few miles from the Great Wall.

Hubble poster
The Hubble Space Telescope's majestic view of the Eskimo Nebula. This spectacular poster is available now from the Astronomy Now Store.