Many asteroid impacts have rocked the Earth. Massive impacts have shaped the Earth – and made life possible.
The young Earth has endured a lot, including one day 3.26 billion years ago when a rock four times the size of Mount Everest collided with the planet. Scientists believe the rock, which was much larger than the Chicxulub body that ended the era of the dinosaurs, likely ended up in the ocean because the Earth was just beginning to form continents.
The impact was so violent that the upper layer of the ocean boiled, creating a tsunami as tall as a New York skyscraper near the impact site. Molten rock rained from the sky. The atmosphere became filled with ash and dust. The planet sank into darkness. But it wasn't all bad.
That was the unexpected conclusion of three presentations at the fall meeting of the American Geophysical Union in San Francisco this month. The scientists, working independently, found that the impacts of giant space rocks on young Earth may have made the planet more hospitable to life.
After disaster comes opportunity: this is a lesson for everyone, and one recorded in the geophysical record. The Earth has been through hell and back again—broken, melted, frozen, depending on which aeon or age it is in.
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How did life originate on Earth?
But the first few billion years of Earth's history remain unclear. No one knows how life emerged and developed, amid the chaos and turmoil that prevailed at that time, into more complex organisms.
The story of how this planet became habitable is important to young astrobiologists, who study the hypothetical existence of life on other worlds. In our solar system, there are many examples of inhospitable planets and moons. Earth is an anomaly teeming with living creatures. What happened to make it like this? As researchers explore the distant past, huge impacts continue to emerge.
“These huge impacts certainly have a negative impact on the atmosphere. If you put too much dust in the atmosphere, it gets very dark,” Nadia Drabon, an early Earth geologist at Harvard University who presented her research at the AGU meeting, said in an interview. “And a lot of the ocean is boiling,” she added. “At the same time, these negative impacts may not have lasted for long.” In their wake, life conditions improved, at least for a while.
The massive tsunami, which may have been caused by an impact 3.26 billion years ago, stirred up the water column in the World Ocean and brought more iron, an important nutrient for metabolism, into shallow seas. Other nutrients have been eroded from land masses into the ocean, Drabon said.
Nick Wogan, a scientist at NASA's Ames Research Center who lectured at AGU, described how early impacts would have given Earth a “hot, steamy atmosphere” but could also have triggered chemical processes relevant to life.
“Early impacts could have had a positive impact on early life in many ways,” said Simon Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who also spoke at the AGU meeting. “For example, they could have provided essential elements or molecules that were missing in the near-surface environment, and may have been important for early life.”
How did impacts shape the Earth?
The young Earth is a mystery because it has left so few records of itself, and scientists must reconstruct it with scraps of evidence and clever computer models. Models suggest it was an aquatic world. Life was sparse and primitive, and nothing even remotely animal-like had evolved. Scientists who study the chemistry of the early atmosphere are not sure whether the sky was blue or orange.
“There was probably an orange haze, maybe like Los Angeles in the 1980s,” says John Tarduno, a geophysicist at the University of Rochester. “You can think of early Earth as an alien planet,” Marchi said.
It was also a planet under attack practically from day one. The early Earth was subjected to constant bombardment for hundreds of millions of years, including a collision with a Mars-sized body that created the Moon.
Impacts contributed to the formation of the Earth
These influences are key to the planet's biography. They contributed to the formation of the Earth itself and added mass to it. The tremors gradually subsided as the debris was removed, but the planet remained vulnerable to catastrophic global impacts. Scientists gave the economic name “S2” to the event 3.26 billion years ago. This was one of the largest of 16 major impacts that scientists have identified between 3.5 billion and 2.4 billion years ago, Marchi said.
These events did not leave the pits. But skilled scientists can find their fingerprints in thin layers of sedimentary rock. The “S” of S2 stands for spherules, small glass-like droplets that rained from the sky after the impact. Spherules and other debris from the impact form a distinct layer in the sedimentary rock, which, like the detective's chalk lines, tells the story of a fatal moment.
However, there was not much that could be killed in those early times. The big leap forward came with the development of bacteria that pump oxygen into the atmosphere. Organisms that use this oxygen as metabolic fuel were added later. Only in the past billion years has life become multicellular, and the first creatures that could crawl across the ocean floor — the first creatures we could call animals — appeared less than 600 million years ago.
Would life on Earth and its infinitely beautiful forms exist without early influences? No one can say that. At that time there were no humans, dinosaurs, or even jellyfish, just bacteria. But microbes are likely well placed to profit from the disaster. They are remarkably resilient and able to survive extreme conditions, such as in Yellowstone's hydrothermal pools or near hot vents on the ocean floor.
“At that time, life was basically very simple organisms. Maybe that's why they were able to survive,” Marchi said. “If we had evolved life like you and me at that time, we would probably have died.”
To the author
Joel Achenbach Reports on science and policy for the National Bureau. He has been writing for the newspaper since 1990.
We are currently testing machine translations. This article was automatically translated from English to German.
This article was first published in English on December 19, 2023 on “washingtonpost.com” was published as part of the collaboration, and is now also available in translation for readers of the IPPEN.MEDIA portals.
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