Geologists, including Tim Johnson from Curtin University, propose that the formation of Earth's first continental crust, which began about 4 billion years ago, was significantly influenced by a barrage of asteroid impacts. This theory suggests that these cosmic events kept the early crust molten and thin, enabling the development of buoyant continents.
Understanding Earth's Early Crust
The oldest known continental rocks date back approximately 4.03 billion years, coinciding with the end of the Hadean eon. The process of how these continents formed remains largely a mystery due to the scarcity of geological evidence. Johnson noted, “There are huge debates about what was going on in the early Earth, because the data is so scarce.” Traditional theories have posited either an active plate tectonics system or the influence of mantle plumes. However, the prevailing models suggest that Earth was too cold for these processes to operate effectively.
“Nobody could make it fit because we did not consider the energy coming from outside of Earth,” Johnson explained, emphasizing the need to include external energy sources in the Earth’s early heat budget.
The Role of Asteroid Bombardment
Johnson's research indicates that asteroid impacts were far more frequent during the early solar system, contributing significant heat to the Earth's crust. The Moon, lacking plate tectonics, provides a clearer picture of the impact frequency during this period. Johnson's team utilized crater counts on the Moon to estimate that Earth must have faced thousands of impacts from bodies larger than 10 kilometers in diameter.
