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A new study says repeated asteroid impacts drove heat deep into the young Earth and kept its crust weak. This suggests heavy bombardment may have helped form continents while erasing most Hadean rocks.
Perth,UPDATED: Jun 29, 2026 10:34 IST
A new study has argued that repeated asteroid impacts on the early Earth did far more than create craters and short-term destruction. The researchers said the heat from these impacts was driven deep into the planet, keeping the young Earth's surface hot, weak and geologically unstable through much of the Hadean eon, the first half-billion years of Earth's history.
The study said this long-lasting impact heating may be central to understanding one of the biggest puzzles in Earth science: why tiny zircon crystals show parts of Earth's surface survived for more than 4.3 billion years and water was present very early, even though almost no intact rocks remain from that period. The oldest known continental rocks are about 4.03 billion years old.
The researchers said large asteroid impacts are often seen as brief surface events, but evidence from the Moon shows such collisions were common in the early Solar System. They said Earth would have been hit even more intensely, with the impacts transferring enormous amounts of energy deep into the planet. In their modelling, they found impact heat was not a small addition to Earth's internal energy budget and, through most of the Hadean, appears to have greatly exceeded heat produced inside the planet itself.
The study said the effect went beyond warming surface rocks. By adding heat and thinning or destroying the crust, large impacts would have caused melting in the mantle beneath impact sites, producing large volumes of basaltic magma. Heat transferred into the mantle from the biggest impacts likely affected volcanism and tectonic behaviour for tens to hundreds of millions of years.
The findings, the researchers said, point to an early Earth that was very different from the modern planet. While some researchers have suggested the early Earth may have resembled today's Earth more closely and may even have had a form of plate tectonics, the new results suggest the early crust was probably thin, weak and partly molten below shallow depths. Rather than a stable outer shell, it may have been repeatedly renewed.
The study also argued that the same impacts may have helped create the continents. Large collisions would have fractured the young crust and allowed water to circulate through it for long periods, changing rocks near the surface. At the same time, melting in the mantle below impact sites would have pushed huge volumes of magma into and through the crust. As this happened repeatedly, the surface became richer in silica, which is seen in the pale-coloured rocks that characterise continental crust.
The researchers said this may also explain why so little Hadean rock survives. If the crust was repeatedly heated, melted and recycled, much of Earth's earliest crust may simply not have lasted. They added that studies of the Moon's impact history show that by about 3.9 billion years ago, the global effect of impact heating in the inner Solar System had become much less important. Around the same time, Earth began to preserve large stretches of continental crust.
The study said that once the period of heavy bombardment eased, the crust would have had a chance to cool, solidify and thicken, making long-lived continents possible. It concluded that repeated impacts may have shaped the young Earth and limited when the planet could begin preserving a lasting crustal record.
With PTI Inputs
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Published By:
India Today Web Desk
Published On:
Jun 29, 2026 10:34 IST
