Earth Suddenly Emerged From The Ocean 2.4 Billion Years Ago

Posted: May 24 2018, 6:55am CDT | by , Updated: May 24 2018, 8:09am CDT, in News | Latest Science News

Earth Suddenly Emerged from the Ocean 2.4 Billion Years Ago
Credit: Ilya Bindeman

Chemical signatures in the Earth's most common sedimentary rock point to a rapid rise of land above the ocean 2.4 billion years ago

Earth was an underwater world in its early history. It was not until 2.4 billion years ago that a significant amount of land rapidly rose out of the ocean and trigged dramatic changes in life and climate.

Earth hard outer layer, called continental crust, is made up of different types of rocks which form continents and Earth’s interior close to the shores. Although much is known about the continental crust, one major mystery remains – how old the crust is? Several theories have been developed with estimates ranging from about one billion to three billion years ago. But geologists are yet to agree on a timeframe. In the latest effort, researchers used shale samples, the Earth's most common sedimentary rock, drawn from all over the world and analyzed triple-isotopes of oxygen inside them that contained traces of rainwater that caused weathering of land from as old as 3.5 billion years ago.

Subtle signatures in shale revealed the chemical history in the rocks and more importantly when land started to emerge from the water and Earth's first supercontinent, Kenorland, and high-mountain ranges and plateaus formed. Previous researches suggested a gradual emergence of land between 1.1 and 3.5 billion years ago. But isotopic changes recorded in the shale samples point to a rapid rise of land above the ocean 2.4 billion years ago.

"Crust needs to be thick to stick out of the water. The thickness depends on its amount and also on thermal regulation and the viscosity of the mantle. When the Earth was hot and the mantle was soft, large, tall mountains could not be supported. Our data indicate that this changed exponentially 2.4 billion years ago. The cooler mantle was able to support large swaths of land above sea level." Lead author Ilya Bindeman, a geologist at the University of Oregon, said in a statement.

The newly emerged land was exposed to weathering by chemical processes at 2.4 billion years ago and began to consume carbon dioxide from the atmosphere. The decrease in greenhouse gases such as carbon dioxide disrupted the radiative balance of the Earth and these atmospheric changes possibly brought significant amounts of free oxygen into the air. The timing also coincides with the transition of life from simple prokaryote in the Archean Eon to the eukaryotes, such as algae, plants, and fungi in Proterozoic Eon.

“In this study, we looked at how weathering proceeded over 3.5 billion years. Land rising from water changes the albedo of the planet. Initially, Earth would have been dark blue with some white clouds when viewed from space. Early continents added to reflection. Today we have dark continents because of lots of vegetation,” said Bindeman. “The process of forming shale captures organic products and eventually helps to generate oil. Shales provide us with a continuous record of weathering."

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<a href="/latest_stories/all/all/47" rel="author">Hira Bashir</a>
The latest discoveries in science are the passion of Hira Bashir (). With years of experience, she is able to spot the most interesting new achievements of scientists around the world and cover them in easy to understand reporting.




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