WAIT, WHAT?
Earth's water was around before Earth
To understand how life emerged, scientists investigate the chemistry of carbon and water. In the case of water, they track the various forms, or isotopes, of its constituent hydrogen and oxygen atoms over the history of the universe, like a giant treasure hunt.
Researchers from the CNRS, Paris-Saclay University, the French Alternative Energies and Atomic Energy Commission (CEA), and the University of Pau and the Pays de l'Adour (UPPA), with support from the Muséum National d'Histoire Naturelle (MNHN), have followed the trail of the isotopic composition of water back to the start of the solar system, in the inner regions where Earth and the other terrestrial planets were formed.
They did this by analyzing one of the oldest meteorites of our solar system, using an innovative method developed just for their study. Their data show that two gas reservoirs existed during the first 200,000 years of our solar system, even before the formation of the earliest planetary embryos.
One of these reservoirs consisted of the solar gas in which all the matter of our solar system originated. With the meteorite, the scientists were able to measure its record directly for the first time ever. The second gas reservoir was enriched in water vapor and already had the isotopic signature of terrestrial water.
It was created by a massive influx of interstellar water in the hot internal regions of the solar system, upon the collapse of the interstellar envelope and the formation of the protoplanetary disc. The early existence of this gas with Earth-like isotopic composition implies that Earth's water was there before the accretion of the first constituent blocks of our planet. These findings are published in Nature Astronomy.Organic makeup of ancient meteorites sheds light on early Solar System
More information: Jerome Aléon, Determination of the initial hydrogen isotopic composition of the solar system, Nature Astronomy (2022). DOI: 10.1038/s41550-021-01595-7. www.nature.com/articles/s41550-021-01595-7
Journal information: Nature Astronomy
Provided by CNRS
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We don't know how life emerged on Earth, but one thing is certain: life as we know it on our planet wouldn't exist without the water that wraps around the surface, runs in rivulets, and falls from the sky.
Our planet is the only one known to have life, and the only one on which liquid water can be found in abundance (moons are another story). There are giant question marks over where and how it came from, but new research suggests that it was here in the Solar System before Earth even formed.
According to a team led by geochemist Jérôme Aléon of the French National Museum of Natural History, isotopes of water in a meteorite from the birth of the Solar System match isotopes of water found on Earth today.
"The initial isotopic composition of water in the Solar System is of paramount importance to understanding the origin of water on planetary bodies but remains unknown, despite numerous studies," the researchers write in their paper.
"Here we use the isotopic composition of hydrogen in calcium-aluminium-rich inclusions (CAIs) from primitive meteorites, the oldest Solar System rocks, to establish the hydrogen isotopic composition of water at the onset of Solar System formation."
Certain types of meteorites can act as time capsules from the birth of the Solar System. A star is born from a cloud of gas and dust that collapses under its own gravity, known as the collapse of the protostellar envelope.
Meanwhile, material in the cloud around it flattens into a disk that feeds into the growing, spinning star. Once it has finished growing, what's left of that cloud forms everything else in that star's system – planets, asteroids, comets, and so forth.
Many of these things are even older than Earth; radiometric dating suggests Earth formed 4.54 billion years ago. And, by sheer luck, some of these rocks land right here on our doorsteps.
The whole accretion process usually heats and squeezes those primordial materials into forms that erase traces of its origins. This has made analysis of its water content a challenge.
Yet there are occasional rock samples that make it to Earth's surface that display few signs of overbaking, providing researchers with a prime opportunity.
The Efremovka meteorite, found in Kazakhstan in 1962, has elements that have been dated back to 4.57 billion years ago. It was this meteorite, and its ancient inclusions rich in calcium and aluminium, that Aléon and colleagues analyzed, using a new technique developed just for this purpose.
To measure the water content of the meteorite, they used focused ion beam imaging to identify and probe all the minerals in their sample, comparing the results with eight terrestrial reference materials with a wide range of water content. Then, they examined the ratio of the isotopes of hydrogen in the meteorite.
These ratios, fascinatingly, can be used to identify the signature of water. Isotopes are variants of an element with different numbers of neutrons; deuterium – also known as heavy hydrogen – has one proton and one neutron. Protium, or light hydrogen, has one proton and no neutrons.
Because hydrogen is one of the components of water, the ratio of these two isotopes in rocks can tell us about the water that rock was exposed to. For example, protium is the dominant hydrogen isotope here on Earth. On Mars, deuterium is the dominant isotope, which tells us that something might be stripping the lighter protium.
The minerals and ratios in the Efremovka meteorite revealed that, in the first 200,000 years of our Solar System's history, before the planetesimals (that's planet seeds) formed, two large gas reservoirs existed. One of these reservoirs contained the solar gas from which the matter in the Solar System ended up condensing.
The other, the team found, was rich in water. This water probably came from a massive influx of interstellar material that fell in towards the inner Solar System at the time of the protostellar envelope collapse.
And, fascinatingly, that water is very similar to Earth's water in its isotopic composition. This suggests that water was present in the early Solar System from its very inception – before Earth was even a twinkle in the protoplanetary disk.
"The ubiquitous hydrogen isotopic composition observed in large, early-formed telluric planetesimals … was reached in the first few 100,000 years of the Solar System owing to a massive influx of interstellar matter infalling directly in the inner Solar System, rather than being produced in a more evolved protoplanetary disk," the researchers write.
The research has been published in Nature Astronomy.
Earth’s water may have seeped up from its depths, as opposed to being delivered by impacts from outer space, according to a new study.
By Becky Ferreira
For a brief period in Earth’s tumultuous early history, a mineral that no longer exists on our planet may have safeguarded the ingredients of water long enough to enable the emergence of oceans that eventually nurtured life.
That’s the conclusion of a recent study led by Xiao Dong, a materials scientist at Nankai University, that presents a new possible origin story for Earth’s water—the most essential ingredient for life as we know it. In addition to yielding new insights into Earth’s ancient oceans, the new study also has implications in the search for water, and therefore alien life, on other planets.
As our young planet was bombarded by asteroids and comets more than four billion years ago, a “now-extinct” permutation of magnesium silicate might have kept hydrogen and oxygen atoms securely locked away deep underground so that they could eventually survive and upwell as liquid water at the surface, according to the study, which appears in Physical Review Letters.
“The origin of water on the Earth is a long-standing mystery, requiring a comprehensive search for hydrous compounds, stable at conditions of the deep Earth and made of Earth-abundant elements,” said Dong and his colleagues in the study.
The team undertook just such a search with the help of an algorithm called Universal Structure Predictor: Evolutionary Xtallography (USPEX) developed by study co-author Artem Oganov, who is a professor at the Skolkovo Institute of Science and Technology. USPEX is able to predict exotic crystal structures to fit a variety of parameters, including compounds that would have existed within the extreme conditions in the interior of our infant planet.
The researchers used USPEX to search for compounds that contain hydrogen and oxygen, the two constituents of water, that would be stable at the high temperatures and pressures that existed hundreds of miles under our planet’s ancient surface. The results revealed a magnesium silicate that is two parts magnesium, one part silicon, five parts oxygen, and two parts hydrogen. This compound “must have existed in the Earth, hosting much of Earth’s water” during “the first 30 million years of Earth’s history, before the Earth’s core was formed, according to the study.
As Earth’s core formed, these silicates disintegrated, a process that released hydrous constituents as water. Over the course of 100 million years, this water made its way to Earth’s surface, where it became the life-sustaining force that still exists today. In this way, these silicates “likely contributed in a major way to the evolution of our planet,” the team said.
These now-extinct compounds may also contribute to the evolution of other planets, which makes them relevant to the search for extraterrestrial life.
Planets that are smaller than Earth, such as Mars, cannot achieve the interior pressures necessary to create these magnesium silicates, which means any water on these worlds had to have a different origin. Meanwhile, planets larger than Earth, such as the tantalizing “Super-Earths” observed in other star systems, would likely support pressures that could preserve huge volumes of these hydrous compounds.
While some scientists have speculated that Earth’s water may have been delivered from outer space by comet impacts, the new study shows that our precious oceans may have emerged from the opposite direction—as byproducts of long-lost compounds hidden deep underground.
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