New research carried out by American scientists and published in the journal Nature Geoscience suggests that our planet may have been an aquatic world , with no continents in sight, some 3.2 billion years ago , when the first life forms emerged, during the stage known as Archaic Aeon. Earth could have been like Kevin Costner’s post-apocalyptic movie “Waterworld,” in which humanity struggles to survive after ice caps have melted and flooded the planet with water.
“Our findings could help scientists better understand how and where single-celled organisms first emerged on Earth, ” said Boswell Wing, a researcher in the Department of Geological Sciences at the University of Colorado Boulder. “The history of life on Earth tracks the available niches. If you have a water world, a world covered by the ocean, then the dry niches just won’t be available. “
Imagine an Earth in which there is no presence of the seven continents of the Earth with imposing mountain ranges and deep valleys.
A world full of water
The researchers performed an isotopic analysis of a sample of ancient oceanic crust from inland northwestern Australia , a geological site called Panorama. They described it as a ‘once-in-a-lifetime opportunity’ to collect clues about ocean water from billions of years ago. The scientists used radiocarbon dating, which tracks the number of carbon-14 isotopes that may have existed in a sample, to estimate the age of the objects to be up to about 60,000 years. For much older objects like rocks, scientists use isotopes of oxygen. In all, they analyzed more than 100 rock samples from across the dry terrain.
“There are no really ancient ocean water samples out there, but we have rocks that interacted with that seawater and reminded us of that interaction,” said Benjamin Johnson, a scientist at Iowa State University. “The process is like analyzing coffee beans. to collect information about the water that is poured through it. “
Scientists were actually trying to take Earth’s early temperature, a question that has proven difficult to answer. It is not clear if the planet was much warmer or colder (or the same as it is today) when life emerged. But the ratio of two oxygen isotopes (natural variations of the element) can be linked to the temperature of ancient oceans due to their different molecular weights. Low-temperature water contains a higher amount of oxygen-16 compared to oxygen-18, and vice versa. “Although these mass differences seem small, they are super sensitive,” Wing said.
After reconstructing a temperature profile of the region 3.2 billion years ago, there was only slightly more oxygen-18 than they would have expected: 3.3%, a much higher percentage than previous estimates.
“Today’s land masses are covered by clay-rich soils that disproportionately absorb heavier oxygen isotopes from water, such as mineral vacuums for oxygen-18, ” the expert continued.
The study authors theorized that the most likely explanation for that excess oxygen-18 in the ancient oceans was that there simply were no continents in the ground to absorb the isotopes . However, that does not mean that there are no areas of dry land around.
“We just don’t believe that there has been a continental soil formation on a global scale like we have today,” Wing explains.
The researchers now plan to explore other more recent rock formations at sites from Arizona to South Africa to see if they can find the exact moment when the land masses we know of today first emerged on the Earth scene.
Was ancient Earth a much warmer world than it is today? Understanding how our planet’s complex geology has taken shape over time can shed light on how life might have ultimately formed.
Referencia: Benjamin W. Johnson & Boswell A. Wing. Limited Archaean continental emergence reflected in an early Archaean 18O-enriched ocean. Nature Geoscience, 2020 DOI: 10.1038/s41561-020-0538-9
