Key Takeaways:
- Recent research suggests Earth was once a water world, with little to no landmass 3 billion years ago.
- Scientists analyzed rocks from Western Australia to determine the water content of early Earth.
- The presence of a heavier oxygen isotope (O18) in the rocks indicates there was less landmass to absorb it.
- If Earth was a water world, life likely originated in ocean environments like hydrothermal vents.
- Studying more rock samples from different periods can reveal when continents emerged.
According to recent research, there was very little to no land in ancient Earth, making it a water world. And that might have a significant impact on how life originated and developed.
Although water covers roughly 70% of the Earth’s surface today, recent research suggests that, three billion years ago, our planet was a true ocean world. Only isolated archipelagos were now visible above the briny surface of our global ocean. If there was any land at all.
The Panorama district of Western Australia provided the scientists with special rock samples from which they based their findings. Because rocks preserve the traces of the environments in which they originated, the scientists concluded that the rocks originated approximately 3.24 billion years ago in a hydrothermal vent system on the ocean floor. Because the rocks were exposed and flipped over the ages, scientists could study Earth’s wet past from the comfort of dry land. They deduced from this that the planet Earth in the past might have been a wet planet with a small landmass.
“An early Earth without emergent continents may have resembled a ‘water world,’ providing an important environmental constraint on the origin and evolution of life on Earth, as well as its possible existence elsewhere,” wrote the authors of the new study, which was published in Nature Geoscience.
Water, water, everywhere
Even though there are many oceans on Earth today, their origins are still a mystery to many. Was water present on Earth from the beginning or did it arrive later? How much later, if at all? And was it asteroids or something else that was the source of the water comets?
Scientists are still pondering these questions and more. This is due to the fact that there is overwhelming evidence that water existed on Earth from shortly after the formation of our planet some 4.4 billion years ago, such as ancient minerals called zircons that appear to have formed in a wet environment. That’s a long oceanic history.
However, it’s less clear how much water early Earth actually had. And by studying their chunk of the ancient seafloor, the researchers were able to probe that question.
The oxygen network
Water imprints its story into rocks as they form. The components of water, or H2O, are always hydrogen and oxygen. However, the kind of oxygen, or isotope, present in the water also provides insight into the conditions under which the water originated. For instance, the temperature or the way the water moved through time between the sea, the land, and the air.
Oxygen comes in two common isotopes. oxygen-16 (O16), a lighter variant with eight protons and eight neutrons. and oxygen-18 (O18), its heavier cousin, which consists of ten neutrons and eight protons. Water molecules containing O16 evaporate more quickly than the heavier O18 versions because of the extra two neutrons that give O18 more weight. Additionally, rocks and dry land are more likely to capture and absorb O18, removing it from the sea stores.
When the authors of the new study examined their chunk of ancient seafloor, they found a lot of O18 — more, on average, than is found in our modern oceans. Furthermore, an abundance of O18 in the early Earth suggests that such a reservoir may not have existed at all because dry land is a massive reservoir of heavy oxygen. The researchers concluded that the lack of dry land emerging from the ancient ocean is the most likely explanation for the excess of heavy oxygen in their sample.
Implications for life
The earliest single-celled organisms on Earth are the subject of much debate among scientists. Did life first emerge near hydrothermal vents in the ocean, where both of heat and mineral-rich water were prevalent? Alternatively, did life originate on land, possibly in the vicinity of Darwin’s suggested small, warm pond? There are many different theories, and scientists are still unsure of the truth.
However, if further research confirms that early Earth really was entirely covered in water, then that knowledge could help researchers further refine their theories of how life came into existence.
“The history of life on Earth tracks available niches,” Boswell Wing, a geology professor at the University of Colorado Boulder, said in a statement. “If you’ve got a water world, a world covered by ocean, then dry niches are just not going to be available.”
Put another way, life could not have originated on land at all if the Earth was completely submerged in water when it first began. And should that prove to be true, it would imply that exoplanets entirely submerged in water could be excellent sites for looking for extraterrestrial life. But let’s hold off on making assumptions just yet.
This Australian seafloor sample covers a sizable and well-preserved area, despite only representing a single point in time. Therefore, the researchers plan to carry out comparable studies on rock samples spanning Earth’s history in order to trace the emergence of the continents. These samples, which span a few billion years of Earth’s history, are waiting to be found in Africa, Canada, New Mexico, and Arizona. Together, they’ll tell the story of when Earth stopped being an aquatic world and started offering up the dry land we inhabit today.
