The very land you’re on right now – provided you’re not reading this on a plane or boat – might have an extra-terrestrial origin story.
That’s the conclusion of a wild new Australian study published this week, which says there’s strong evidence the Earth’s crust – the bit we need to survive, lest we sink into the molten-hot mantle – went through regular growth spurts that line up with the Solar System’s passage through dense parts of the galaxy.
“The Solar System orbits around the Milky Way, passing between the spiral arms of the galaxy approximately every 200 million years,” said lead researcher Chris Kirkland of Curtin University.
“When passing through regions of higher star density, comets would have been dislodged from the most distant reaches of the Solar System, some of which impacted Earth.
“Increased comet impact on Earth would have led to greater melting of the Earth’s surface to produce the buoyant nuclei of the early continents.”
The prevailing theory is that the crust, the continents which float on it, were produced via internal mechanisms which started a few billion years ago.
“As the heat increased, some of Earth’s rocky materials melted and rose to the surface, where they cooled and formed a crust,” National Geographic explains.
Just as some scientists are now wondering if life was brought here from elsewhere in the cosmos – panspermia – it seems the very land we live on might have extra-terrestrial origins too.
“Linking the formation of continents, the landmasses on which we all live and where we find the majority of our mineral resources, to the passage of the Solar System through the Milky Way casts a whole new light on the formative history of our planet and its place in the cosmos,” said Kirkland.
But don’t worry about another bombardment just yet – the last one big enough to be considered crust-forming, in this analysis, happened about 168 million years ago, so we’re not due for a while yet.
The paper was published this week in Geology.