A Saint Louis University geologist has unearthed further evidence in his mounting case that shifting of the continents -- and perhaps life on Earth -- began much earlier than many scientists believe.
Tim Kusky, a professor of Earth and atmospheric sciences, has discovered the world's first large intact pieces of oceanic mantle from the planet's earliest period, the Archean. The nearly mile-long section of rock, which is billions of years old, may hold clues as to when life developed on the planet. The major finding was reported today in the July issue of GSA-Today -- the premier journal of the Geological Society of America.
Working with colleagues from Peking University, Kusky uncovered the rare find at a site near the Great Wall where last year the team discovered the planet's oldest complete section of oceanic crust. Reported in Science, their work recently was heralded by the Chinese government as one of the most significant scientific findings of 2001.
This latest discovery may prove even more remarkable. For years, scientists have longed to find large pieces of the planet's deep interiors. But until now, they've had to rely on only tiny fragments to study. Formed tens of kilometers below the ancient sea floor, this new discovery's massive mantle rocks are preserved in a highly faulted belt 100 kilometers long.
Unlike the sea floor samples Kusky found last year, the mantle rocks preserve 2.5 billion-year-old minerals that hold clues to the origin of plate tectonics. The minerals, including an unusual type of chromite deposit only known from deep ocean floor rocks appear to have been deformed at extremely high temperatures before they were completely crystallized by volcanic
This shows that the mantle rocks were flowing away from the ridges on the oceanic floor, evidence that the continents began shifting more than 500 million years earlier than now widely believed. Because the discovery shows that the plates were moving in that early period, these findings could have a more far-reaching effect on theories related to the development of life on the planet. Just when single-celled organisms 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, Kusky said it's possible that life developed and diversified around these vents as the plates started stirring.
Kusky and Peking University's J.H. Li have initiated a series of studies on the section of ancient mantle and it's minerals aimed at understanding the conditions of the Earth 2.5 billion years ago. Their work is being funded by U.S. National Science Foundation, the Chinese National Natural Science Foundation, Saint Louis University and Peking University. The Chinese government also has dedicated a natural geologic park at the site of the discovery.
Saint Louis University is a leading Catholic, Jesuit, research institution ranked among the top 50 national, doctoral universities as a best value by U.S. News & World Report. Founded in 1818, the University strives to foster the intellectual and spiritual growth of its more than 11,000 students through a broad array of undergraduate, graduate and professional degree programs on campuses in St. Louis and Madrid, Spain.
Tim Kusky at Saint Louis University
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