Huge Meteor Impact 3 Billion Years Ago May Have Spurred Evolution

Billions of years ago Earth was bombarded with meteorites of all sizes and shapes. Approximately 3.26 years ago, the biggest of these, which is known as S2, hit the planet in an area of what is now South Africa with such force that it radically altered the global environment. Scientists estimate this object was the size of four Mount Everests, which is why its destructive power was so vast. But new research suggests that this meteorite impact event may have helped spur the development of life on the planet, creating changes that jump-started evolution and ultimately allowed complex lifeforms to appear.

In a study just published in the Proceedings of the National Academy of Sciences (PNAS), a team of scientists led by early-Earth geologist Nadja Drabon from Harvard University describe a scenario that explains why a gigantic meteorite striking the planet so long ago might have had a creative impact.

“We think of impact events as being disastrous for life,” Drabon stated in a Harvard press release. “But what this study is highlighting is that these impacts would have had benefits to life, especially early on … these impacts might have actually allowed life to flourish.”

The meteorite essentially stirred up the ocean environment where it hit, changing the chemistry of the water to provide more nutrients to the primitive bacteria and other single-cell microbes that occupied the planet’s seas at that time. This encouraged the proliferation of bacteria that were more suited to taking evolutionary leaps in the future, unleashing Earth’s life-creating capacities in earnest.

Graphical depiction of the S2 meteorite impact and its immediate after-effects. (Drabon et al./PNAS)

A Realistic Scenario of Post-Catastrophe Evolution

For the purposes of the new study, Drabon and her team visited the Barberton Greenstone Belt in South Africa, a rocky stretch of land where geological evidence of the S2 impact can be found. This area was underwater 3.26 billion years ago, but it is exposed now, giving researchers an opportunity to collect and examine rock samples and ancient sediments from the time when it was covered by the sea.

Analysis of the chemical composition of such samples can offer clues about past conditions on the planet. In this case the results of the analysis showed how changes caused by the S2 impact altered the ancient ocean environment, which Drabon and the rest of her team say might have helped Earth’s earliest lifeforms prosper.

Drabon with students David Madrigal Trejo and Öykü Mete during fieldwork in South Africa. (Photo courtesy of Nadja Drabon/The Harvard Gazette)

In the scenario that Drabon and her colleagues describe, the S2 meteorite slammed into the Earth with a force up to 200 times greater than the asteroid that killed off the dinosaurs 66 million years ago. Hitting the ocean the way it did, it caused the biggest tsunami the planet has ever seen, stirring up the waters from their greatest depth as the top layer of the ocean boiled away from the heat of the impact.

At the same time the collision literally ripped up the seabed, leading to the ejection of massive quantities of dust and debris into the atmosphere, plunging the planet into darkness. The heat was distributed throughout the atmosphere as well, causing a dramatic spike in global temperatures.

This sounds like devastating and un-survivable catastrophe. But the situation was more complex than this.

The single-celled bacteria that lived at that time were too hardy to be killed off by this process. Suddenly the waters they swam in were filled with phosphorus and iron, the former brought by the meteorite and the latter stirred up from the ocean’s watery depths.

Both of these elements are crucial to life, and with increased supplies bacterial life forms experienced a population explosion. Bacteria that can metabolize iron did particularly well, and this rapid blooming of life acted as a catalyst for future evolution.

“This [the sudden increases in phosphorus and iron in the ancient oceans] adds to the possibility that giant meteorite impacts, typically seen as agents of destruction and extinction, carried transient benefits to life early in Earth’s history,” the study authors wrote in their PNAS article.

“Our work suggests that on a global scale, early life may have benefited from an influx of nutrients and electron donors, as well as new environments, as a result of major impact events.”

Rock and thin section images of the Bruce’s Hill and Umbaumba sections. (Drabon et al./PNAS)

Searching for the Secrets of Life on Earth at the Beginning of Time

To find the evidence that made this study possible, Drabon and her students and colleagues spent a significant amount of time hiking through the mountain passes of the rugged Barberton Greenstone Belt. They were searching for rocky remnants of past meteorite impacts, which they were eventually able to find after digging around in the Earth’s crust.

The chemical signatures of these small rocks and stones revealed a lot about what had happened in the region more than three billion years ago, allowing Drabon and the other experts involved in this study to piece together a realistic post-catastrophe scenario that could have boosted the prospects of bacterial life.

There is some speculation involved in their theory, as they would readily admit. But speculation is inevitable when scientists are trying to figure out how life first evolved billions of years in the past.

South Africa’s Barberton Greenstone Belt contains evidence of seven other massive impact events besides the S2. Drabon and her team plan to return to the region often, as they seek to learn more about how ancient meteorite strikes altered the environment and affected the lifeforms that existed at the very dawning of Earth time.

Top image: Artist’s impression of a meteor strike.           Source: Andrii/Adobe Stock

By Nathan Falde