Earth's buoyant continental crust appeared around 4 billion years ago, but the mechanism behind its formation has puzzled geologists for decades. Tim Johnson from Curtin University argues that intense asteroid impacts during the Hadean eon provided the heat necessary to create these silica-rich continents, challenging previous theories focused solely on internal processes.

The Hadean period spans Earth's first 500 million years, yet geological evidence from this era is nearly nonexistent due to plate tectonics recycling the surface. Johnson's team turned to lunar samples and crater counts to estimate impact frequency on early Earth. Their modeling revealed thousands of impacts exceeding 10 kilometers in diameter, delivering significantly more heat than previously accounted for.

Impact heating exceeded radiogenic and core heat by roughly tenfold during the Hadean, keeping the crust thin and largely molten. This prevented plate tectonics from operating, as the lithosphere couldn't remain rigid enough for subduction. Material cycled back into the mantle to depths of 600 kilometers, explaining why so little Hadean crust survived.

As impact flux declined between 3.9 and 3.5 billion years ago, internal heat sources became dominant. The mantle cooled and crust thickened to approximately 30 kilometers, enabling plate tectonics and continental formation. Recent discoveries in Canada's Nuvvuagittuq Greenstone Belt of 4.2-billion-year-old mafic rocks support this timeline. The research suggests early Earth's geological evolution hinged on external bombardment rather than purely internal heat.