New evidence suggests that the Earth was a water planet without continents 3.24 billion years ago. Scientists from the University of Colorado at Boulder analyzed isotopic values from rock samples in the Pilbara-Kraton in Australia, one of the oldest known rock formations on the planet. The analysis showed that the seawater 3.24 billion years ago had an excess of O-18 isotope compared to today’s oceans. This suggests that there were no processes that bound the heavy O-18 oxygen isotopes, which would have reduced their concentration in the water. The most likely explanation for this is the absence of landmasses, which would have caused weathering and the formation of clay soils that bind heavy oxygen isotopes.
The study, published in the journal Nature Geoscience, supports previous studies that suggest large landmasses on Earth emerged 2.7 billion years ago. The researchers believe that the Earth may have gone through two different equilibrium states of the water cycle, one before the emergence of the first continents and one after. However, it remains unclear when plate tectonics began and when the first continents formed.
The study’s lead author, Benjamin Johnson, explained that there are no samples of ancient seawater, but they have rocks that interacted with the seawater at the time and preserved those interactions. The researchers analyzed the ratio of oxygen isotopes O-16 and O-18 in more than 100 samples of 3.24 billion-year-old rock to determine the temperatures of the Earth at the time, geochemical processes, and sediment deposition. The study suggests that the Earth was almost entirely covered by water 3.2 billion years ago, with only mini-continents protruding from the oceans.
The findings shed new light on the Earth’s early history and could help scientists better understand the planet’s evolution. The researchers plan to conduct further studies using the same methodology to examine younger rock formations and narrow down the timeframe for the emergence of continents.
