Violent planetary collisions may explain why Earth became habitable

New research from Southwest Research Institute reveals that violent late-stage planetary collisions shaped Earth’s water, atmosphere, and tectonics. These impacts may explain planetary diversity and why Earth became uniquely habitable Mars.

When we think of Earth as the cradle of life, it’s easy to imagine a gentle process that led to oceans, air, and fertile ground. But new research suggests that our planet’s habitability may actually be the result of violent chaos — specifically, the catastrophic collisions that marked the final stage of planetary formation.

A team led by the Southwest Research Institute (SwRI), in collaboration with Yale University, reviewed decades of planetary science to understand how late-stage impacts shaped the inner rocky planets — Mercury, Venus, Earth, and Mars. Their study, published in Nature Reviews, highlights how the final 1% of planetary growth, known as “late accretion,” may have determined whether worlds ended up barren or capable of supporting life.

Cosmic construction zones

Planets form from swirling disks of gas and dust around young stars. Over millions of years, smaller bodies collided and merged, creating larger and larger worlds. By about 100 million years into this process, Earth had nearly reached its full size. But the final sliver of growth — that last 1% — delivered enormous impacts that brought crucial ingredients, stripped away old atmospheres, and even re-shaped planetary interiors.

According to lead author Dr. Simone Marchi of SwRI, these impacts weren’t just finishing touches. They influenced tectonics, surface chemistry, and atmospheric balance — factors that ultimately set Earth apart from its neighbors.

Why Venus and Earth turned out so differently

The team’s simulations suggest that Venus endured higher-energy collisions than Earth. Those massive impacts likely superheated Venus’s core, fueling intense volcanic activity that resurfaced the planet and helped create the hellish atmosphere we see today.

Earth, by contrast, seems to have received a gentler sequence of impacts — ones that not only delivered water but also helped maintain the conditions for plate tectonics and long-term climate stability. These differences may explain why one world teems with life while the other became an uninhabitable furnace.

Collisions that deliver and destroy

Collisions had a dual role. Some stripped atmospheres away, leaving planets bare, while others delivered volatile elements such as carbon and water — essential for life as we know it. “These processes almost certainly played a role in the prebiotic chemistry of early Earth,” said Marchi, though how exactly they influenced the origin of life is still an open question.

Understanding Earth’s collision history doesn’t just explain our own past — it also helps guide the search for life beyond the Solar System. A rocky planet’s mass, size, and orbit may put it in the habitable zone, but without the right kind of impact history, it may never develop the conditions to support life.

In short, Earth’s story is one of survival through violence. Our oceans, atmosphere, and ability to sustain life may all trace back to a series of cosmic smash-ups billions of years ago — the very chaos that transformed a rocky world into our living planet.