How asteroids may have sparked life on Earth

To reach these conclusions, the researchers modeled the early history of asteroid impacts on Earth. Their simulations showed that these powerful collisions fractured the planet's crust, creating porous underground pathways that allowed water to circulate through the upper layers of the crust.

The team used a sophisticated shock physics code that simulates how high speed impacts break apart solid rock and create permeable regions. This is the first comprehensive study to measure how asteroid impacts generated permeability, an important property that allowed fluids to move through the early Earth's crust.

"This modeling is both novel and crucial for understanding the earliest environments life may have emerged from," said SwRI's Amanda Alexander, first author of an AGU Advances article describing the research. "While often considered catastrophic in the context of dinosaur extinction, impact bombardment was also likely critical for creating environments for prebiotic chemistry."

How Asteroids Reshaped Early Earth

Earth formed about 4.5 billion years ago and soon entered an era of intense asteroid bombardment. These high velocity impacts shattered enormous volumes of rock beneath the surface while vaporizing material and scattering molten rock across the landscape.

The tremendous heat generated by each collision, combined with the planet's natural geothermal heat, likely drove hot water through the newly fractured crust. The resulting hydrothermal systems, comparable to the network of geysers around Yellowstone National Park, may have created favorable settings for the origin and early evolution of life.

To better understand this process, the researchers simulated asteroid impacts spanning a range of sizes and speeds. They also tested different crustal compositions and temperature conditions before calculating how much fractured, water permeable crust each impact produced.

According to the simulations, a single large impact during this early period could have generated as much as 100 times the hydrothermal activity found across the Yellowstone region today.

"Because life could have originated or evolved in hydrothermal environments, it is important to understand and quantify the generation of these systems by impacts on the early Earth," Alexander said, noting that additional research will be needed to better define the characteristics of these ancient hydrothermal systems.

Long Lasting Effects on Earth's Crust

The models indicate that the amount of fractured, permeable rock created by an impact depended mainly on the energy of the collision, which was controlled by the asteroid's size and speed. At the same time, the degree of permeability within those fractured regions was influenced by the Earth's geothermal gradient and the composition of the crust. The researchers also incorporated estimates of how frequently these impacts occurred.

"Using a bombardment history model to infer the cumulative effects of recurring impacts, we estimate that the upper 5-mile (8-kilometer) shell of the Earth's crust likely was highly permeable 4.3 billion years ago and that a significant portion of this volume may have remained permeable until 3.5 billion years ago," Alexander said. "These results show that impacts were instrumental in driving hydrothermal changes to the early Earth's crust, with important consequences for the geochemical evolution of near-surface environments."