Enzo Campetella Meteored Argentina 09/30/2024 16:40 7 min
The result of recent scientific research provides information that threatens to change some consolidated paradigms. The our planet Earth may have had fresh water about 500 million years earlier than previously thought, as revealed by Eos. The study in question, published by Nature Geoscience, indicates that this revealing information was obtained from tiny grains of zircon from Australia dating back about 4,000 million years ago.
The research was able to determine that already about 4 billion years ago the planet had oceans but also exposed crust which allowed the hydrological cycle and the appearance of fresh water necessary for life as we know it.
According to the scientists who worked on this research, the minerals contain evidence of continental precipitation, providing new evidence that the early Earth had a continental crust as well as oceans. The widespread interaction between meteoric (fresh) water and the continental crust that emerged on the early Earth may have been key to the emergence of life, although it is not known precisely when the hydrological cycle began.
The research used the oxygen isotopic composition of zircon crystals in Western Australia to determine when the hydrological cycle began. It is an immersion in the Hadean eon, one of the first phases of the Precambrian periodwhich ended about 3.8 billion years ago.
At the time, a very young planet was home to little more than rock, magma and water. Data on this very ancient period is scarce, so this new analysis represents a good contribution to scientists’ understanding of how our planet formed, Eos indicates.
Looking back to Earth’s beginnings
This discovery could help scientists determine more precisely when life emerged on Earth. Fresh water and exposed continental crust were two of the conditions necessary for life to arise. Today the first evidence of life could be the Australian stromatolites dating back 3.5 billion years. But now this new work shows that “we had the same conditions about 4 billion years ago,” as indicated by study co-author Hamed Gamalledien, a geochemist at Khalifa University in the United Arab Emirates.
The oldest stones on the planet are found in Western Australia. Immersed in more recent rocks appear zircon crystals dating back to the Precambrian era. Image: CCIn conclusion, the discovery moves the timeline corresponding to the beginning of life on the planet back by about 500 million years. Said like this, it is just a number, but if we compare it with the existence of human beings, it is an enormity. The existence of our species does not go beyond 2 thousandths of that time. And very little remains of that primitive land or it is difficult to access.
The Earth of that Hadean era has almost disappeared over time. Most rocks have been weathered or subducted deep into the crust, Eos says. Some of the only remaining Hadean minerals are zircon crystals embedded in younger rocks. Zircon is hard and resistant to chemical alteration and contains small fragments of uranium that allow scientists to date them. It also contains oxygen, which was key to the new discovery.
The key is in oxygen
Technically, researchers explain that oxygen has three stable isotopes, which are O-16, O-17, and O-18. The ratio of light oxygen O-16 to heavy oxygen O-18 is influenced by terrestrial processes such as evaporation and condensation, and deviations from the standard ratio have long been used by paleoclimatologists as an indirect indicator of temperature.
Details of the geological area where the studies were conducted in Western Australia. Image: Hamed GamalledienDelta-O-18 is a measure of the deviation in the ratio between the stable isotopes O-18 and O-16. Now, delta-O-18 from some Australian zircons was used in this research. It has been proven that it is very likely that at that time the planet had a solid crust, as well as oceans of liquid water, unlike a rotating globe filled with magma oceans as previously imagined.
For the study, samples were taken from Jack Hills in Australia, a region known to contain the oldest zircon crystals on Earth. They dated some of the collected grains to an age of 3.4 billion years and others to around 4 billion years ago, before the end of the Hadean. The researchers were able to demonstrate that these zircons were formed by interacting with fresh water resulting from the evaporation of ocean water.
They are rocks that have interacted with fresh water, not ocean water. And if the rocks interacted with fresh water, that must mean there was land protruding above the ocean, suggesting that the Earth had continental crust as early as 4 billion years ago.
References to the scientific study:
Gamaleldien, H., Wu, LG., Olierook, H.K.H. et al. Onset of the Earth’s hydrological cycle four billion years ago or earlier. Nat. Geosci. 17, 560–565 (2024).
