Geology | Meteorites have left lasting impact on Earth

Dale Gnidovec For The Columbus Dispatch

Feb 9, 2020 at 6:01 AM Feb 9, 2020 at 10:41 AM

Geological processes on Earth typically move very slowly. But the impact of a meteorite, a rock from space, is one example of changes that occurred on Earth very quickly.

Geological processes on our planet generally work slowly. The continents move at between a leisurely pace of half an inch per year (about as fast as your fingernails grow) to a blistering 5 inches per year (about as fast as your hair grows). Mountains rise at about a tenth of an inch per year and are reduced to small hills over millions of years.

But occasionally things happen quickly. One example is the impact of a meteorite, a rock from space. The most famous one occurred 66 million years ago, when a rock about 6 miles across hit Mexico‘s Yucatan Peninsula. The ensuing environmental effects resulted in the extinction of 75% of the species on Earth, including the non-avian dinosaurs.

Scientists have found about 200 impact craters on our planet. That is not many, given Earth‘s 4.6-billion-year history. We‘ve certainly been hit by many more, but Earth heals its wounds through erosion and subduction.

Some recent research by scientists from Australia, London and NASA found the oldest known impact crater on Earth. Located in the Australian Outback, the Yarrabubba structure is 2.2 billion years old, 210 million years older than the Vredefort Dome in South Africa and 380 million years older than the Sudbury structure in Ontario, Canada.

Unlike Meteor Crater near Winslow, Arizona, the Yarrabubba is not a crater you can easily see – most of it eroded long ago. There is an elliptical magnetic anomaly 7 by 12 miles from a crater that originally was about 40 miles in diameter, caused by a meteorite that was about 4 miles wide.

What makes the date of the impact so significant is what also happened at that time, an episode geologists call Snowball Earth. The recent Ice Age of the past 2 million years – the Pleistocene – saw ice advancing as far as 39 degrees south latitude, where Cincinnati is today. During Snowball Earth, ice might have reached the equator, covering the entire planet.

Snowball Earth ended rather abruptly at about the time of the Yarrabubba impact, and the scientists suggested that impact triggered massive global warming. Hitting the ice at 45,000 miles per hour would have created huge amounts of water vapor, which is a more powerful greenhouse gas than carbon dioxide.

One problem with that idea is that water vapor doesn‘t stay in the atmosphere very long, averaging about nine days, which probably wasn‘t long enough to bring an end to Snowball Earth.

Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University. gnidovec.1.edu

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