May 14, 2009 -- Earth's violent tremors and fiery volcanic eruptions are commonplace today, a natural outgrowth of plate tectonics. But it wasn't always so. According to a new study, the planet's geologic engine mysteriously shut off 2.4 billion years ago. Volcanoes went on a 250-million year hiatus, and the atmosphere cooled until the world's first glaciers sprouted on the ancient continents. "There was a widespread slowdown, maybe even a shutdown of plate tectonics," said Kent Condie of the New Mexico Institute of Mining and Technology in Socorro. "Earth may have reverted into a stagnant lid state of cooling." Stagnant lid tectonics is an alien style of geology, thought to have occurred on Mars and still be active on Venus. Venus is so hot that the mantle is too soupy to force rocky plates into one another, or tear them apart. Instead the crust sits like a single, solid skin on the planet. Related Content:
Earth was a similar place billions of years ago, still fresh from the crucible of our young solar system. It may have undergone several periods of stagnant lid tectonics before the mantle cooled enough for plate tectonics to kick in, around 3.0 billion years ago. Condie believes the lull in activity he and his colleagues have discovered is evidence that the stagnant lid came back one last time. Their work is published in the June issue of the journal Earth and Planetary Science Letters. The quiet period may have had major consequences for global climate. Oxygen first emerged in the air in large quantities around 2.4 billion years ago, supplanting what had been a methane-dominated atmosphere. With volcanoes nowhere to be found, carbon dioxide was in short supply, and global temperatures plummeted. There is evidence from rocks in China, North America and Australia that the first glaciers appeared around this time, too. Get More NewsSpiders, Scorpions Among World's Oldest CreaturesMany creepy crawlies have been on Earth much longer than previously believed.Blood-Sucking Vampire Bats Sing DuetsWhite-winged vampire bats "harmonize" with separated roost mates.Oldest Hebrew Writing Possibly FoundAncient inscriptions on a 3,000-year-old pottery shard could make history.Rare, Prehistoric-Age Reptile Found in N.Z.A tuatara has been spotted on the New Zealand mainland for the first time in 200 years.Iceman Has No Living RelativesOetzi, the 5,300 year-old frozen mummy, left no living genetic legacy.SLIDE SHOW: Landscapes of TerrorWhat makes a place feel scary? There are scientific explanations.It's Official: People Are Warming the PolesHumans are conclusively to blame for polar warming, say scientists.Eight-Armed Animal Preceded DinosaursWhat may be one of Earth's first animals was no bigger than a coaster and had eight arms.Phoenicians Live on in People's GenesOne in 17 Mediterranean men may be descended from ancient Phoenicians.Pesticides, Fertilizers Linked to Frog DeclineA pesticide is found to promote parasites among amphibians.Hubble Telescope Taking Photos AgainThe Hubble Space Telescope is once again snapping stunning photos of the universe.Andean Mummy Hairs Show Hallucinogen UseScientists find direct evidence of hallucinogenic drug use among ancient Andeans.Opals on Mars Reveal Planet's Long Wet PastOpals found on Mars suggest the planet has been wet for much longer. |
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