By India Ashok
What was our home planet like hundreds of thousands of years ago? Scientists are still attempting to unravel this particular mystery. Over the years, conflicting theories have emerged about the early days of Earth’s history. While some researchers suggested that our planet was a harsh, frozen ball of ice, other theories suggest that Earth was a boiling mass of extreme heat that was too inhospitable to sustain life.
However, a new study by scientists from the University of Washington suggests that ancient Earth had much milder and stabler temperatures than previously thought. The new research could also lend hope to scientists hunting for alien worlds that could host life.
“Ideas about the early Earth’s environment are all over the place, from a very hot world, to one locked in a permanent ice age, from a world with acidic oceans to one with seawater so alkaline it would sting your eyes,” David Catling, a professor of earth and space sciences at the University of Washington, said in a statement. “These simulations show that our early world had about the same average temperature as today, and a seawater pH within roughly one unit of neutral.”
Previous research estimated that around four to two and a half billion years ago, during the Archean era, the Earth’s temperatures were around a freezing minus 25°C. However, other estimates have put our planet’s temperatures at the time as high as 85°C. At these high temperatures, the only form of life that can thrive are microbes that are now generally found in hot springs. However, according to the new research, early Earth’s temperatures ranged from zero to 50°C.
Our results show that Earth has had a moderate temperature through virtually all of its history, and that is attributable to weathering feedbacks they do a good job at maintaining a habitable climate, Joshua Krissansen-Totton, a doctoral student at the University of Washington and first author of the new study, said in a statement.
How scientists figured out our planet’s past temperature
The new study significantly narrows the possible temperature of the early Earth to 0 to 50 degrees Celsius. Credit: Joshua Krissansen-Totton/University of WashingtonIn order to come up with their estimates, the scientists created a computer simulation of the Earth’s temperature over the past four billion years. The simulation included the most recent data and analysis of how rocks, oceans and air temperatures interacted with each other and our planet’s environment. The researchers’ calculations also took into account the latest data on how the seafloor withstood the brunt of time, under various different conditions.
“Seafloor weathering was more important for regulating temperature of the early Earth because there was less continental landmass at that time, the Earth’s interior was even hotter, and the seafloor crust was spreading faster, so that was providing more crust to be weathered,” Krissansen-Totton said.
To get a comprehensive picture of Earth’s average air temperature and ocean pH through billions of years, the researchers ran several simulations, aimed at gathering estimates of the size of the continents, the temperature sensitivity of chemical weathering and more.
“We got this initial answer that early Earth had moderate temperatures and slightly acidic ocean pH,” Krissansen-Totton said. “I tried really hard to break that, looking for assumptions that could possibly change that answer. But I found that this is a really robust result. It’s hard to imagine a realistic scenario where temperatures or pH were more extreme.”
“The results help us understand how natural processes kept Earth’s environment suitable for life to carry on for billions of years, from its humblest beginnings to the wonderful forms now around us,” Catling said.
Good news for alien hunters
The research’s results likely provide hope to scientists searching for extraterrestrial life on other planets. This is based on the scientific assumption that if Earth’s temperature was tamer and milder throughout its history, then other planets located within the habitable zone could also possess stable enough climatic conditions for alien life to have evolved.
“There’s nothing particularly remarkable about these processes,” Krissansen-Totton added. “They can occur on any rocky planet with oceans. So other planets that are in the habitable zone are likely to have their climates stabilized to moderate values by these weathering feedbacks. And that’s a good thing for the search for life, because you need moderate temperatures for billions of years to have a stable environment for life to evolve.”
The new research has been published in the Proceedings of the National Academy of Sciences.