Small moons might have rained down on the early Earth, splattering it with debris that helped shape our young world and potentially built the first continent.
快猫短视频s have long suspected that the moon was formed when a Mars-sized object named Theia collided with the proto-Earth roughly 100 million years after the formation of the solar system. The crash threw molten rock into orbit that coalesced to form our planetary companion. But at the Technion Israel Institute of Technology in Haifa, Israel, and his colleagues argue that the crash wasn鈥檛 a singular event.
He says we鈥檝e missed a fundamental aspect in the formation and evolution of the Earth 鈥� that it was pummelled time and time again. So Perets, and his colleagues modelled those many collisions.
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Dangerous tango
The study adds a new twist to recent work, which speculates that the moon was formed by a large number of impacts as opposed to a single collision, says at the University of Arizona, who was not involved in the study.
鈥淣ot only was the Earth struck by multiple impactors, but it was then re-impacted by the debris and moonlets that were created by those impacts in the first place,鈥� he says.
Indeed, the team argues that multiple impacts would have likely blown debris back out into orbit, which would have coalesced to form the moon and many smaller moonlets. The complex dance between those moonlets would change their orbits as they gravitationally perturb one other. As their orbits become more elliptical, many of them would come crashing back down onto the young Earth.
Like a localised storm, the so-called 鈥渕oonfalls鈥� would have poured hefty amounts of material on one spot alone 鈥� an effect that might have built large-scale structures on Earth, including the first continent.
Long-lost continents
The idea that impacts can cause topographic features isn鈥檛 terribly wild. 快猫短视频s suspect that the mountainous region on the far side of the moon, for example, is actually the remains of a smaller moon that slammed onto the surface long ago. And similar features can be seen on planets across the solar system.
But at the University of California, Santa Cruz, disagrees that early moons would have formed any terrestrial topographic features. That鈥檚 because it took roughly 100 million years for the Earth to cool from a molten ball of magma and form a thick crust. As such, infalling moons would have had to strike the Earth after 100 million years to leave their mark 鈥� but the team鈥檚 research shows that they fall earlier. 鈥淚t鈥檚 a race against time,鈥� he says.
Perets, however, argues that the debris would have been brought to the Earth after most of the planet had solidified. And the impact would have been gentle enough that the material wouldn鈥檛 have mixed in with Earth鈥檚 interior. 鈥淭he debris therefore settles on the upper layer of Earth鈥檚 mantle and can in principle exist there to this day,鈥� he says.
Still, scientists will be hard-pressed to find evidence today, says at Curtin University in Bentley, Australia. He finds the moonfall scenario plausible, but the oldest preserved continental crust is 4 billion years old, so any processes that occurred during the first 600 million years of Earth鈥檚 history have been completely erased.
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Read more: The moon may have formed in a vaporised, doughnut-shaped Earth
