The Earth Was Once a Snowball. An Asteroid Impact Two Billion Years Ago May Have Changed That

An asteroid that crashed into Earth over two billion years ago may have helped bring a period known as Snowball Earth to an end. By analyzing minerals at the site of the Yarrabubba impact crater in Western Australia, scientists have been able to determine that the date of impact—2.229 billion years ago—was the same point when Earth started to thaw following an extreme ice age.

Snowball Earth is the term used for periods when most of the planet is covered in ice. This has happened several times over Earth's history, with research suggesting the earliest instance took place 2.3 billion years ago. What caused this ice age and why it ended is unknown, although many hypotheses have been put forward. They include shifts in plate tectonics that lead to an increase in magmatism, which resulted in more carbon dioxide being released.

In a study published in Nature Communications, researchers led by Timmons Erickson, from NASA Johnson Space Center and Curtin University, Australia, have now found another possible explanation.

The researchers have announced that the 43-mile-wide Yarrabubba impact crater is the oldest preserved structure of its kind in the world. Aaron Cavosie, one of the study authors from Curtin University, said the team had been trying to find the exact date the asteroid hit using precise dating techniques. "When the dating results came in, it blew our hair back," he told Newsweek.

He said the first "smash" result, which showed the impact crater was the world's oldest, was shortly followed by the date matching up with the point glaciers disappear from the geological record. "People knew about the end of the glaciation previously, but argued about what the trigger was," he said. "We don't know how much ice was on Earth at the time of the impact, but the evidence suggests there were glaciers."

In their study, the team worked out what would have happened if the asteroid, estimated to be between three and six miles wide, had hit a landscape covered in ice. Their findings show a huge amount of water vapor, which is a greenhouse gas, would have been ejected into the atmosphere.

Their simulations used a 4.3-mile-wide asteroid, which if it hit ice, would have resulted in the release of between 87 trillion and 5,000 trillion kilograms (192 trillion and 11,023 trillion pounds) of water vapor.

"Water vapor is a very efficient greenhouse gas, even more so than CO2," Erickson told Newsweek. "If the Earth was in a Snowball period then the atmosphere would have been rather dry and thus the impact produced water vapor may have acted as a significant radiative insulator leading to the warming of Earth's atmosphere. The important factor is the residence time of water in the Earth's atmosphere after the impact, which currently is not known."

Where Western Australia sat on the globe 2.229 billion years ago is unknown. Scientists also do not know whether the continent was covered in ice at this time. This is something the researchers hope to determine in future research, as well as finding more impact sites, Erickson said.

Christopher Spencer, from Queen's University in Ontario, Canada, published research in 2018 that identified a 52-million -year lull in magmatic activity globally. The Yarrabubba impact took place during this lull, Cavosie said. "The take-away point is that it's unlikely that volcanic outgassing caused the glaciers to melt, given the paucity of magmatic activity at that time," he said.

Commenting on the latest study, Spencer, who was not involved in the research, told Newsweek the findings present a "potential causal link between large bolide impacts and dramatic swings in climate."

He explained: "The Rhyacian Period [2,300 to 2,050 million years ago] is arguably the most enigmatic time in Earth history and represents a significant lull in tectonic and magmatic activity...The four phases of Rhyacian glaciation are interlaced with intervals of warm water limestone deposition. These dramatic swings in climate were likely mediated by biologic and/or volcanic activity. What seemed to be an equilibrium condition—similar to the annual seasons—abruptly ended 2.25 billion years ago."

Spencer said that when the asteroid that killed the dinosaurs hit, some models suggest atmospheric temperatures rose by 260 degrees Celsius for at least 20 minutes. "Undoubtedly, a bolide that struck a planet covered in ice would result in a similar upheaval of Earth's climate and surface processes," he said. "The paper by Timmons et al. opens the door for a new way of viewing the interaction between impact processes and the evolution of Earth's climate."

asteroid artist impression
Artist impression of an asteroid in space. Researchers say an impact event 2.229 billion years ago coincided with the end of a Snowball Earth period. iStock
The Earth Was Once a Snowball. An Asteroid Impact Two Billion Years Ago May Have Changed That | Tech & Science