September 29, 2023

New Study Suggests Earth’s Water Didn’t Come from Comets or Asteroids

Author: Jonny Lupsha, News Writer
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By Jonny Lupsha, News Writer

An identification of space rocks indicates Earth was always wet, Science Alert reported. One long-held belief about the origins of water on Earth was that distant comets and asteroids brought water here, but soon it may be proven false. Earth’s cooling helped form oceans as well.

Ocean and cliff
In current times, about 96.5% of the Earth’s water is found in the oceans, while about 71 percent of the Earth’s surface is covered by water. Photo by Gunnerchu / Shutterstock

According to Science Alert, new evidence contradicts a theory that Earth was dry upon its formation and water came to the planet from traveling space rocks, such as comets.

“According to early models for how the solar system came to be, the large disks of gas and dust that swirled around the Sun and eventually formed the planets were too hot to sustain ice,” the article said. “Scientists therefore theorized that the water came along after, and the prime suspects were meteorites known as carbonaceous chondrites that are rich in hydrous materials.

“But the problem was that their chemical composition doesn’t closely match our planet’s rocks.”

A new study by a French team of scientists suggests that another group of meteorites called enstatite chondrites are chemically much closer to Earth’s rocks. This would make them Earth’s inner building blocks rather than travelers. The Earth’s cooling would have helped this process.

Just Blow on It

If water wasn’t transported to the planet, how did we get our oceans?

“Through gradual cooling of the surface, liquid water [from volcanoes] began to accumulate,” said Dr. Harold J. Tobin, Professor of Geoscience at the University of Wisconsin–Madison. “The surface cools down enough that first pools, then bigger pools, lakes and bodies of water in low spots start to form on the Earth. This begins a process of dissolution of minerals.”

As the water breaks down minerals on the surface of the Earth, Dr. Tobin said it starts a process called the rock weathering cycle. It also makes the water take on some salinity as dissolved salts get mixed up into the ocean.

A Planet of Ocean and Ice

While liquid water from volcanoes and the gradual cooling of the Earth’s surface provided water that covered portions of the Earth, the amount of dry land as we know it today may have been much less.

“That water starts to accumulate and form an ocean, and in fact, some recent studies suggest that an ocean—a liquid water surface—may have completely covered the Earth’s surface at about four billion years ago,” Dr. Tobin said.

“The reason this is a possibility is that the Sun at that time was probably faint and put out less heat than it does today. Not only did the ocean cover the entire solid surface of the Earth, but in fact, it also covered [the surface] with ice to a depth of several hundred meters, at this time very early in Earth’s history.”

However, Dr. Tobin said, it isn’t likely that an ice-covered Earth lasted very long. Eventually, evaporation increased and our ice planet melted.

If proven true, the research suggesting that the planet had contained moisture since its formation will likely shake things up for Earth sciences. New scientific discoveries happen all the time, but it’s not often that they involve something as old as the planet itself.

This article was proofread and copyedited by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.

Dr. Harold J. Tobin

Dr. Harold J. Tobin contributed to this article. Dr. Tobin is Professor of Geoscience at the University of Wisconsin–Madison. He earned his BS in Geology and Geophysics from Yale University and his PhD in Earth Sciences from the University of California, Santa Cruz.

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