New research led by 麻豆直播 and QUT (Queensland University of Technology) has revealed repeated asteroid impacts may have been the dominant force shaping the early Earth, delivering vast amounts of heat into the planet鈥檚 interior and delaying the formation of stable continents.
The study suggests that during the 鈥� more than four billion years ago 鈥� Earth was struck far more frequently than today, with each impact injecting energy deep into the planet.
Rather than a relatively stable early planet, the findings point to a much hotter, weaker and more unstable Earth, closer to the extreme conditions long proposed by scientists.
Lead author , from the within the School of Earth and Planetary Sciences, said the research challenged the idea large impacts were simply brief surface events.
鈥淭here is a temptation to think of large impacts as short-lived events that scar a planet鈥檚 surface and then pass,鈥� Professor Johnson said.
鈥淏ut the early Solar System was full of collisions, and the Moon preserves that history in plain sight. Those impacts carried enormous amounts of energy, and that energy had to go somewhere.
鈥淭he extra heat from impacts would have kept much of the early crust weak and partially molten, making it difficult for rocks to survive.
鈥淎t the same time, those conditions would have helped produce more silica-rich crust, which later became the foundation of the continents.鈥�
Co-lead author Professor Craig O鈥橬eill, from QUT, said the team鈥檚 modelling showed the effects of impacts extended far beyond the moment of collision.
鈥淥n the early Earth, much of that energy would have been transferred into Earth鈥檚 mantle, the thick layer immediately beneath the crust, as heat,鈥� Professor O鈥橬eill said.
鈥淭hat would have caused mantle beneath and around the impact site to rise and melt, producing large volumes of magma.
鈥淥ur results suggest the early crust was thin and unstable for much of the Hadean, not a world with strong plates behaving in a familiar modern way.
鈥淚nstead, impacts would have helped keep the crust hot, weak and mobile, while driving melting and recycling on a planetary scale for tens to hundreds of millions of years after the initial collision.鈥�
The findings also help explain why almost no rocks survive from the first 500 million years of Earth鈥檚 history and why long-lived continents appear to have formed only after the intensity of impacts declined.
Professor Johnson said the timing of this shift was striking.
鈥淚t is apparent from the Moon that, by around 3.9 billion years ago, the global effect of impact heating becomes much less important, which is also around the time Earth begins to preserve continental crust. That seems unlikely to be a coincidence,鈥� Professor Johnson said.
Macquarie University also contributed to the study, titled 鈥業mpact heating and the hidden Hadean鈥�, and published in Science, and found online here:
