Does a planet need life to create continents?

Earth may not have possessed the continents it does now if not for life, instead becoming a planet covered nearly entirely in ocean.

If not for life, Earth may not have possessed the continents it does now, instead becoming a planet covered nearly entirely in ocean, researchers say.

These new findings suggest that any continents astronomers may one day see on alien worlds may potentially be signs of extraterrestrial life, scientists added.

Earth is currently the only known planet in the universe that has liquid water on its surface.

There is life virtually wherever there is liquid water on Earth, so one main focus of the search for extraterrestrial life as we know it is the region around a star where it is neither too hot nor too cold for liquid water to exist on a planet, an area known as the star's habitable zone.

Although water covers most of Earth's surface, nearly 30 percent of the planet is covered by land, sustaining a dazzling variety of life.

Scientists might one day be capable of telling if distant planets are similarly covered by land, oceans and clouds by looking for reddish, bluish or grayish tints in the colour of those worlds.

Researchers have already developed maps of clouds on a giant planet orbiting a distant star.

Now researchers suggest Earth would have been a water world with very few continents, if any at all, without the presence of life.

A great deal of research has shown that life has had a major impact on the evolution of Earth's atmosphere and oceans.

Plants and other photosynthetic life generate oxygen, giving Earth the only known atmosphere in the universe with significant levels of oxygen.

Life also greatly influences how much carbon is in the atmosphere and oceans in the form of carbon dioxide and methane.

These greenhouse gases trap heat and can dramatically affect Earth's climate, which in turn has an effect on how much of Earth's water is frozen as ice.

Oxygen can also indirectly cool Earth's climate by removing methane from the atmosphere—in fact, the dramatic rise of oxygen in Earth's atmosphere about 2.4 billion years ago, known as the Great Oxidation Event, may have cooled the planet enough to for it become a frozen "Snowball Earth."

"However, much less is known about whether life has had any effects on the deeper interior of Earth," said study author Tilman Spohn, a planetary scientist at DLR, the German Aerospace Center's Institute of Planetary Research in Berlin.

Past research noted the oldest signs of life found so far are roughly 3.5 billion years old, about the same time continents began growing, and suggested a potential link between these events.

The scientists then explored whether or not the evolution of life on Earth could have influenced the evolution of the planet.

The investigators focused on biological weathering, by which life breaks down rock.

This crumbled rock gets blown and washed away by wind and water, sediment that eventually makes its way to subduction zones, the areas where one tectonic plate of the Earth's crust dives or subducts under another.