Source: AGU Advances
Asteroids and planetesimals regularly bombarded Earth between about 4.6 billion and 3.5 billion years ago, in the Hadean and Archean eons. Because few rocks today are more than 4 billion years old, our understanding of the planet’s environment during that time is limited. However, samples from the Moon and its cratered surface hint at the period’s rate of cosmic impacts.
Early asteroid strikes were responsible for significant changes in Earth’s crust, which was primarily basalt-like at the time. The shock waves from collisions fractured the crust and increased porosity, allowing fluids and gases to move through the rocks. Prior research suggests that the resulting hydrothermal systems—such as the network of geysers around Yellowstone National Park—provided the environment for the origin and evolution of early life on Earth.
Alexander et al. explored how surface impacts during the Hadean and Archean allowed fluids and gases to maneuver through crustal environments. The authors built a large suite of impact simulations with the iSALE shock physics code, toggling parameters such as basalt crust thickness, geothermal gradients, and the presence or absence of a 5-kilometer-deep ocean. The simulations detailed how collisions on the surface shaped permeability in the crust. They then integrated a model for ancient bombardment data to understand the cumulative effects of repeated strikes over time.
The results indicate that prior to 4.3 billion years ago, impacts may have made the crust far more permeable, particularly in its top 8 kilometers. From the simulations, the authors inferred that the size of permeable regions was dependent on impact energy, and that geothermal gradients and rock composition in the crust affected the degree of fragmentation after impact. These porous domains formed potential settings for prebiotic chemistry within the early crust.
The research is the first comprehensive study of impact-generated permeability in early Earth’s outermost layer. The results provide a novel framework for evaluating how bombardment influenced hydrothermal circulation and geochemical alteration during the Hadean and Archean eons, with implications for our understanding of life’s origin and evolution in Earth’s earliest days. (AGU Advances, https://doi.org/10.1029/2025AV002097, 2026)
—Aaron Sidder, Science Writer
