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Complex Life Conditions Came Earlier on Earth
By SPACE.com Staff
posted: 10:27 am ET
21 May 2001
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The Earth's massive land slabs were on the move much earlier in the planet's history than previously assumed, a researcher says, and that means complex life had enough heat and food to evolve then too Earth's massive land slabs were on the move much earlier in the planet's history than previously assumed, a research team says, and that means complex life had enough heat and food to evolve then too. It has been widely held that plate tectonics, or the motion of Earth's plates and continents, dates back 1.9 billion years, but geologist Timothy Kusky at St. Louis University worked with a team of scientists that found data showing the plates began moving much sooner. Last summer near the Great Wall of China, Kusky discovered the oldest complete section of displaced oceanic sea floor on the planet, which is more than 500 million years older than previously documented. Kusky and Robert Tucker of Washington University in St. Louis then obtained dates on the rare samples. "This discovery shows that the plate tectonic forces that create oceanic crust on Earth today were in operation more than 2.5 billion years ago," Kusky said in a prepared statement. That would date them back to Earth's earliest geologic time period -- the Archean. Earth is about 4.6 billion years old and fossil evidence shows life extending back to 3.8 billion years ago. So Kusky's findings could have a more far-reaching effect on theories related to the development of life on the planet. The team's results were published in the May 11 issue of the journal Science. Archean debates The rocks studied by Kusky and his colleagues are similar to much younger volcanic rocks that erupted on the seafloor in a process known as seafloor 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 early Earth. Ophiolites are rock structures formed on the seafloor when continents collide.
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 seafloor 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.
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