Quote:Some 4.5 billion years ago, a Mars-sized object smashed into the nascent Earth, spinning off our moon. Now a team of scientists proposes this giant impact did even more: The collision left behind mysterious blobs within Earth’s interior that may have helped kick off plate tectonics — the geologic process that fuels earthquakes, volcanoes and generally allows life to exist on our planet.
The idea, fleshed out with computer modeling in a new study in the journal Geophysical Research Letters, is an attempt to answer one of the most fundamental questions about our home world.
We live on the only planet known to have a surface made up of rocky plates that slide around and crash into each other at boundary zones as the superhot interior churns. This subterranean drama usually goes unnoticed on human time scales, except when an earthquake strikes or a volcano erupts. But most experts agree this process is absolutely essential to life as we know it because it helps the planet cycle carbon, which is important to keeping the climate habitable.
What experts don’t agree on is how plate tectonics started.

 
One theory — published in the journal Nature last year — offers an explanation, but also raises a few eyebrows. It suggests that after the moon-forming object slammed into our planet, bits of it ended up intact in Earth’s interior.
The new paper takes this idea a step further: Around 200 million years after the impact, these submerged blobs could have helped create hot plumes inside Earth that disrupted the nascent surface, breaching the crust and allowing circular slabs to sink — a process called subduction.
This process, the authors say, could explain why the oldest minerals on Earth are zircon crystals that appear to have undergone subduction more than 4 billion years ago. What’s more, they suggest it might have contributed to the rise of modern plate tectonics.