Study: "Building blocks" of Earth may have brought water to the planet, not comets or asteroids
By virgiliomarin // 2020-08-30
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A recent study suggests that most of Earth's water did not come from comets or asteroids that crashed on baby Earth. Instead, water was already present since the planet formed. An international team of researchers looked at rare earth rocks that are thought to be the building blocks of Earth. They found that these rocks, called enstatite dendrites, contained abundant amounts of hydrogen that were more than sufficient to supply the water of Earth's present-day oceans. The findings were surprising as most scientists theorized that water came from an external source. This theory assumes that Earth was dry at the time of its formation. And only upon the landing of an asteroid or a comet did water appear. "The most interesting part of the discovery for me is that enstatite chondrites, which were believed to be almost 'dry,' contain an unexpectedly high abundance of water," said co-author Lionel Vacher of Washington University in St. Louis. The findings of the study were published in the journal Science.

Rare pristine rocks may be source of Earth's water

Enstatite dendrites are good objects of study for investigating the planet's origin and the early solar system. They are likely made up of the same materials that formed young Earth. Previous research found that both rocky bodies share striking isotopic similarities: Enstatite chondrites have similar oxygen, calcium and titanium isotopes as Earth, which indicates that their hydrogen and nitrogen isotopes are similar as well.

However, most geoscientists assumed that enstatite chrondites formed too close to the sun. As a result, the rocks were often considered dry, prompting scientists to avoid any exhaustive search of hydrogen in them.

For the study, the researchers examined pristine enstatite chondrites -- rocks that were neither altered on Earth nor on their asteroid during the early years of the solar system.

Using conventional mass spectrometry and secondary ion mass spectrometry, the team was able to measure the content and composition of hydrogen in the meteorites. Because hydrogen reacts with oxygen to produce water, knowing how much hydrogen is in the rocks would indicate how much water the rocks contributed to young Earth.

The researchers found that the amount of hydrogen in the rocks could contribute to three times more than the current volume of today's ocean waters. They also posited that a large amount of atmospheric nitrogen, the most abundant gas in Earth's atmosphere, could have come from the pristine rocks.

These findings show that enstatite chondrites, identified to be the building blocks of the planet, may explain the origin of Earth's water.

Protosolar nebula led to Earth's oceans

Another study published in the journal Science also proposed that Earth's water came from a native source. In this case, the researchers proposed that water came from protosolar nebula, clouds of dust and gas that eventually clumped together to form Earth. They first studied basaltic rocks that are thought to have originated from deep within the mantle. They examined hydrogen isotopes present in the rocks and found light isotopic signatures. Based on measurements of Jupiter and the solar wind, which were found to preserve chemical signatures of the protosolar nebula, the team suspected that nebular water had an extremely light hydrogen isotopic signature. The isotopic correspondence between the rocks and protosolar nebula implies that water was present since Earth formed. However, there's some criticism to this model. Scientists said that temperatures would be too hot during the accumulation of protosolar nebula, which means water would immediately evaporate. But the researchers said that water molecules could have adsorbed or stuck onto dust particles, as previous models showed. (Related: Scientists believe the Earth had water before we had the moon, according to surprising new study.) While the "dry Earth" hypothesis is for some the more plausible explanation, these two studies offer compelling evidence that Earth, in fact, might have had water as early as 4.5 billion years ago. This has important implications for the search for water in space: It implies that other planets might have also preserved water throughout the processes that led to their formation. Cosmic.news has more on water in outer space. Sources include: DailyMail.co.uk ScienceMag.org
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