We don’t know for sure how life arose on Earth, but one thing is for sure: Life as we know it on our planet would not exist without the water that surrounds the surface, flowing in streams and falling from the sky.
Our planet is the only planet we know of known to have life and an abundance of liquid water. There are huge questions about where and how this water came from, but new research shows that it was in the Solar System before Earth was formed. A team led by geochemist Jérôme Aléon of the French National Museum of Natural History said that the water isotopes in a meteorite from the birth of the Solar System match the water isotopes found on Earth today.
“The initial isotopic composition of water in the Solar System is of great importance for understanding the origin of water in planetary bodies, but remains unknown despite a great deal of research,” the researchers write in their paper. We use the isotopic composition of hydrogen in calcium-aluminum-rich inclusions (CAIs) from primitive meteorites, ancient Solar System rocks.”
Some 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 primordial stellar cover.
Meanwhile, the material in the surrounding cloud turns into a disk that feeds the growing, spinning star. When it’s finished growing, what’s left of that cloud; it makes up everything else in that star’s system, such as planets, asteroids, comets, and the like.
Many of these are even older than Earth; Radiometric dating shows that Earth formed 4.54 billion years ago. And quite by chance, some of these rocks land on our planet. The entire process of accumulation often heats these primitive materials and compresses them into forms that erase any traces of their origins. This complicates the analysis of water content.
Still, some rocks that show little signs of overheating make it to the Earth’s surface on rare occasions, giving researchers a fantastic opportunity. The Efremovka meteorite found in Kazakhstan in 1962 has features determined to be 4.57 billion years old. It was this meteorite and its ancient calcium- and aluminum-rich inclusions that Aléon and colleagues analyzed using a new technique developed for this purpose.
To measure the meteorite’s water content, they used focused ion-beam imaging to identify and probe all the minerals in their samples and compared the results to eight terrestrial reference materials with a wide range of water content. They then examined the ratio of hydrogen isotopes in the meteorite.
Impressively, these ratios can be used to determine the signs of water. Isotopes are variants of an element with different numbers of neutrons. Also known as heavy hydrogen, deuterium has one proton and one neutron. Protium, or light hydrogen, has a proton and no neutrons.
Since hydrogen is one of the components of water, the ratio of these two isotopes in rocks can give us information about the water to which the rock is exposed. For example, protium is the predominant isotope of hydrogen on Earth. On Mars, deuterium is the dominant isotope, which could tell us something might be losing the lighter protium.
Minerals and proportions in the Efremovka meteorite indicate that two large gas reservoirs existed in the first 200,000 years of Solar System history, before planets (i.e. planetary seeds) formed. One of these reservoirs contained solar gas, which caused the condensation of matter in the Solar System.
The team found that the other was rich in water. This water likely came from a massive stream of interstellar matter falling towards the inner Solar System during the collapse of the protostar cover.
And yet impressively, this water is very similar to Earth’s water in its isotopic composition. This huge similarity also suggests that water has first been present in the Solar System since its beginning, before there was even a twinkling in Earth’s protoplanetary disk.
As the researchers write, “the ubiquitous hydrogen isotopic composition observed on large, early-formed telluric planets was achieved during the Solar System’s first few 100,000 years, thanks to a massive flux of interstellar matter falling directly into the Solar System, rather than being produced in a more advanced protoplanetary disk. ”
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