Researchers discovered how impacts from giant meteorites may have helped jump-start the tectonic processes and the magnetic field of early Earth.
An international study, led by scientists from Macquarie University in Australia, found that impacts from massive meteorites could have caused subduction - a process described as "where the solid outer section of the Earth sinks into the deeper mantle at ocean trenches" by the study's lead author Associate Professor Craig O’Neill from Macquarie University.
"This would have effectively recycled large portions of the Earth’s surface, drastically changing the geography of the planet,” explained O'Neill.
Movement between the plates at subduction zones, where tectonic plates converge, causes modern-day earthquakes.
The bombardment by the meteorites also may have started up the Earth's magnetic field by forcing the planet's outer crust to suddenly move down into the planet's outer core. According to Professor O'Neill, this "affects convection in the core, and thus the geodynamo – the process that creates the Earth’s magnetic field."
The effect of impacts on mantle dynamics. Credit: Macquarie University.
So far little is known about the first 500 million years of Earth's life, called the Hadean eon (about 4.56 to 4 billion ago) and considered the planet's dark ages as far as geology is concerned. Little crust has been preserved from that period, hindering our understanding of early tectonic activity. There is evidence that suggest Earth at that time might have been covered by what was esentially a "lid" on the surface, very different from the actively moving tectonic plates of today.
O'Neill notes that if we are to look at Earth as "part of an evolving early solar system," where similar processes were taking place, then it's possible to see how the meteorite impacts could have caused subduction. What's more, there was a period around 4 to 4.1 billion years ago, when the initially low magnetic field was suddenly strengthened to present-day values.
“This is a really important age in the inner solar system," said O'Neill. "Impacting studies have suggested a big disturbance in the asteroid populations at this time, with perhaps a big upswing in impacts on the Earth. Our simulations show that larger amounts of meteorite collisions with the planet around this time could have driven the subduction process, explaining the formation of many zircons around this period, as well as the increase in magnetic field strength.”
Dr. Simone Marchi from the Southwest Research Institute in the U.S., who co-authored the study, stressed the "strong connection" between meteorite hits and the planet's geophysical evolution.
“One has to wonder, how much of the current Earth, and other terrestrial planets, is the result of collisions that took place eons ago?” Dr. Marchi asked.
You can check out the study here, published in Nature Geoscience.