Where does our planet’s water resource come from? It is possible that not only comets from afar have supplied the water retrospectively, new study results suggest: Contrary to previous assumptions, most of the precious liquid could also come from the same material that led to the formation of the earth. This is evident from the evidence of surprisingly high hydrogen contents in rare meteorites, which correspond to the substance that was present in the inner solar system when our planet was formed.
It is the trademark of our blue planet and the elixir of life – against the background of the importance of water, uncertainties about its origin seem almost surprising. But common models for the formation of the solar system cause inconsistencies: According to them, the earth should actually be dry. Because it was previously assumed that the formation material of the inner planets including the earth was too hot due to the proximity to the sun to contain large amounts of water. Only the planets and celestial bodies of the outer solar system were made from material that contained water in the form of ice. So far it has been assumed that most of the water was only supplied to the planet after the earth was formed, namely by meteorites and comets that came to earth from the cooler outer regions of the solar system. But this explanation also still raises questions.
Where did the blue treasure come from?
But this explanation also still raises questions. It is based on the basic assumption that the earth’s original building material was actually very dry. So far this has not been clearly demonstrated. In this context, the material of very rare meteorites, which only make up around two percent of the pieces in global collections, is representative of the original substance: the so-called enstatite chondrites (EC meteorites) have isotope signatures of certain elements that correspond to those of the earthly material. It is therefore believed that their composition corresponds to the substance that became the educational material of our planet in the youth of the solar system.
But so far there have been difficulties in determining the original water content of the enstatite chondrites. “Enstatite chondrites were commonly considered to be ‘dry’ and this well-established assumption has likely prevented efforts to analyze hydrogen content,” says lead author Laurette Piani of the University of Lorraine in Vandœuvre-lès-Nancy. But she and her colleagues have now devoted themselves to the task. “There are few pristine enstatite chondrites – those that have not been altered either on their asteroid or on Earth. In our study, we carefully selected the sample material and applied a special analysis method in order to avoid distortion from the entry of terrestrial water, ”explains Piani. Specifically, they examined material from 13 enstatite chondrites using mass spectrometry methods in order to precisely record the content and composition of the small amounts of water in the meteorites.
More water than expected
The researchers were able to show that the enstatite chondrites contain significantly more hydrogen than previously assumed. Projections and modeling of the formation of the earth then showed that enstatite-chondrite-like materials could have supplied enough hydrogen to the growing proto-earth to form at least three times the amount of water in today’s oceans on earth.
Other results also fit into the picture, the scientists report: It was already known that enstatite chondrites have similar oxygen, titanium and calcium isotopes to terrestrial material – the study now shows that the hydrogen and nitrogen isotopes also match those are similar to the earth. “If enstatite chondrites were indeed the building blocks of our planet – which their similar isotopic composition suggests – then this result means that these types of chondrites could have supplied the earth with enough water to explain the origin of the earth’s water,” sums up Co- Author Lionel Vacher of Washington University in St. Louis.
So far, the researchers cannot say when the material inflow relevant for the later water resource took place. According to them, however, it must have occurred quite late in the course of the Earth’s formation so that the still young and hot planet could hold the volatile substance. Anne Peslier from NASA’s Johnson Space Center in Houston also sees the results as an important contribution to research into the origin of the earth’s water. In a comment on the study, she writes: “The work of the scientists now brings an important element into the discussion: Perhaps the water simply came from the same mist of matter from which the earth was created”.
Source: Washington University, Article: Science, doi: 10.1126 / science.aba1948