When land first rose above water, it transformed Earth’s climate

The Earth may have undergone a drastic transformation 2.4 billion years ago with a rapid rise of land above the ocean, according to a new study.

Researchers from the University of Oregon examined isotopes in shale samples from all over the world and found nearly imperceptible traces of rainwater.

This points to the possibility that during Earth’s early years, newly exposed land underwent dramatic weathering that would have triggered changes in the Earth’s geographic makeup, climate, and even life.  

The study was published in the journal Nature and the results show that land weathering may have occurred as early as 3.5 billion years ago.

The researchers analyzed three oxygen isotopes, oxygen 16, the rare but stable 17 and 18, in 278 shale samples taken from every continent and spanning 3.7 billion years.

After identifying changes in the ratios of the isotopes in the shale, the researchers were able to better establish when newly exposed crust, after rising above sea level, was exposed to chemical and physical weathering such as rainfall.

The results also coincide with previous hypotheses about when the Earth’s first supercontinent was formed with mountain ranges and plateaus.

“Crust needs to be thick to stick out of water,” said Ilya Bindeman, the study’s lead author. “The thickness depends on its amount and also on thermoregulation 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.”

The surface temperature during this time was likely hotter by several tens of degrees that what we see today according to the researchers.

Not only does the study provide a possible timeframe for the development of major land formations and weathering, but the rise of land above sea-level at this time coincides with the transition from the Archean Eon to the Proterozoic Eon when algae and plants first emerged.

The stepwise changes in triple-isotopes of oxygen in the shale show that land emerged in a stepwise pattern between 1.1 and 3.5 billion years ago and 2.4 billion years ago, the land began to absorb carbon dioxide.

The study’s results show how the world’s first landmasses emerged and when chemical weathering took place, changing the world’s climate. The newly formed landscapes would have even led to changes in the reflection of solar radiation.

“What we speculate is that once large continents emerged, light would be reflected back into space and initiate runaway glaciation,” said Bindeman. “Earth would have seen its first snowfall.”

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By Kay Vandette, Earth.com Staff Writer