Persistent Early Islands May Have Provided The Cradles For Life On Earth

Early Earth was mostly a water world, undermining one of the main theories about how life formed. However, new modeling of the way radiation levels shaped Earth's crust suggests islands may have been more common and lasted longer than previously thought. Michael S. Helfenbein

Earth's crust probably behaved differently 4 billion years ago than it does today, thanks to higher radioactivity. In seeking to understand the consequences, two geologists realized it would likely have allowed chains of islands to stay above the surface of the oceans longer than had previously been acknowledged, increasing the opportunities for life to appear.

Supporters of the two main competing sites for the origins of life have spent decades arguing their cases without convincing each other. One group favors geothermal vents at the bottom of the ocean, the other prefers Darwin's proposal of a “warm little pond.”

A significant problem with the pond idea is where it might have been sited, given the likely lack of continental crust on early Earth. Without continents, oceans would have covered almost the whole planet.

Volcanic activity would likely have forced up chains of islands, like Hawaii today. Today volcanic islands are relatively short-lived, leading many to question whether life would have had the time to not only appear, but evolve to the point where it could survive its original habitat being overtaken by the surrounding seas. However, Dr Juan Rosas of Mexico's Ensenada Center for Scientific Research and Higher Education and Yale's Professor Jun Korenaga think they have the answer to this problem.

In Nature Geoscience, Rosas and Korenaga note the Earth began with more uranium than it has today, most of which has decayed to stable elements. The extra radioactivity undoubtedly generated more heat within the planet, and the authors think this created more lumpiness than geologists have allowed for. This, the pair argue, would have made some ocean basins considerably deeper than others.

Where the sea bed was closer to the surface, island chains pushed up by volcanic activity would have sometimes had a second life as exposed seamounts. These might have offered much more suitable environments for life to form than if islands quickly eroded away as soon as their volcanic activity stopped.

The evolution of volcanic islands to seamounts as it operates today (a) and on an early Earth where the radioactivity made the crust much hotter. Rosas and Korenaga/Nature Geoscience

One theory for life's origins relies on meteorites carrying nucleobases landing in contained water to provide the raw materials for life to get started. Problematically, despite the rain of asteroids the Earth experienced at the time, this would seem to require either a lot of ponds, each pond to last a long time, or an extraordinary amount of luck.

Eventually we know continents started to establish themselves, offering still more opportunities for life to form. However, at the time life is thought to have appeared, continental crust is thought to have been limited to pockets of what is now Western Australia and Greenland small enough they wouldn't have hosted much water. The existence of lost continents, since pulled apart by tectonic forces, remains debated.

If Rosas and Krenaga are right the early Earth had more islands at any one time, and therefore more bodies of water suited to supporting life if the appropriate materials were provided.

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