When she was very young, planet Earth looked a little different than the one we know and love today.
On the one hand, there were supercontinents on it – when the land on which we currently live was located in different configurations, as it was pushed by tectonic movements.
But there may have been a period when there was very little or no land, and, according to new research, the Earth was completely covered with water.
Geological research suggests that about 3.2 billion years ago, our current homeworld, which is 4.5 billion years old, was covered by the global ocean.
If confirmed, such a conclusion could resolve questions about how life began about 3.5 billion years ago; in particular, whether it originated in freshwater bodies of water on land or in salty seas. If there were no land areas for fresh water, the issue is moot.
“The history of life on Earth tracks the available niches,” explains geobiologist Boswell Wing of the University of Colorado at Boulder. “If you have a water world, a world covered by an ocean, then dry niches simply won't be available.”
The research team actually tried to measure the early temperature of the Earth, a question that has long haunted scientists. It is unclear if the planet was much warmer or cooler (or about the same temperature as today) when life began.
But the ratio of the two isotopes of oxygen – the natural variation of the element – may be related to the temperature of ancient oceans due to their different molecular weights. Lower temperature water contains more oxygen-16 than oxygen-18, and vice versa.
There is no seawater 3.2 billion years old to analyze. But there are rocks of that age that used to be at the bottom of these ancient oceans, such as the Panorama area in the Pilbara region of Western Australia. These rocks preserve the chemical history of the oceans, including the well-preserved hydrothermal vent system.
But even after researchers reconstructed the region's temperature profile 3.2 billion years ago, oxygen-18 was slightly higher than they expected at 3.3 percent. This is about 4 percent more than in today's relatively ice-free ocean and much higher than previous estimates.
According to simulations, the researchers found that the ratios in the rock samples could be explained by the absence of continents. This means that the planet was completely wet, like Enceladus or Europa.
“There is nothing to suggest that tiny micro-continents were not protruding from the oceans,” Wing said. “We just don't think about the global formation of continental soils as we do today.”
Of course, then the question arises: when exactly did the continents appear, displaced from the ocean by tectonic plates, merging together? This is the next step of the study. The team plans to explore younger rock formations to try and piece together this graph.
The study was published in the journal Nature Geoscience.
