Conventional wisdom among geologists has always been that the first several million years in Earth's 4.5 billion-year history were an age of lava and fire. Nothing could possibly live in on the burning planet until at least 3.2 billion years ago - or so scientists thought. A new study of 4 billion-year-old rocks (at left above) published in Nature reveals the early Earth (right) may have been fairly chilly, and also packed with life.
Called the Hadean period in reference to the Greek term for hell (Hades), the first 700 million years of Earth's history was a time when the planet was bombarded by deadly meteorites. Now, however, most geologists have accepted the idea that single-celled organisms could have lived through these catastrophic hits. And the article just published in Nature reveals that the early planet probably had land masses and bodies of water.
By examining zircons, a type of crystal found in 4 billion-year-old Australian rocks, a team of U.S. scientists determined not only that water had been present in the area at the time, but that the rocks had existed in a chunk of cooled planetary crust caused by plate tectonics. Plus, the planet was likely a lot cooler than previously imagined, though probably hotter than it is today.
The temperature difference would have been caused partly by plate tectonics, which leeches greenhouse gasses from the air as it churns the Earth's crust. But that temperature would also have been affected by the weakness of the young sun, which put out 30 percent less energy than it does today.
These new theories about the early Earth help explain why geologists have discovered signs of life blooming all over the planet starting about 3 billion years ago. In fact, life was probably evolving for as much as a billion years before that. And except for those occasional apocalyptic meteor hits, life evolved on a planet whose climate might not have been all that different from the one we experience today.
Low Heat Flow Inferred from Zircons [via Nature]
A New View of Early Earth [via NYT]
Image via New York Times (Left, Bruce Watson; right, Don Dixon).