Where did Earth's water come from? New study suggests it could have originated from a rare type of meteorite
Water may have arrived on Earth from an unlikely source, by hitching a ride on a type of meteorite that was once considered dry, a new study suggests. These meteorites or space rocks contained enough hydrogen to deliver at least three times the amount of water present in the Earth's oceans.
About 70% of our planet is covered with water — but a lot about its origins are unclear. "Why planet Earth has water is fascinating. For one, without water, we would not exist — no life," Dr Anne Peslier from NASA Johnson Space Cente, tells MEA WorldWide (MEAWW). "But scientists have had a hard time explaining how Earth could have water. It formed too close to the Sun," says Dr Peslier, who is not involved in the study. She wrote a perspective on the findings.
According to the new study, Earth's water could have come from a rare group of meteorites called Enstatite chondrites. They are forged from materials floating in the inner solar system, which are likely the same ingredients that helped Earth form. The finding suggests that water may have arrived from a closer source, rather than meteorites from the outer solar system.
With this, the study presents a new theory to explain the origins of water. Previous ones have suggested that another class called carbonaceous chondrite meteorites, which come from water-rich outer solar systems, are likely sources. But their isotopic composition differs from Earth — making them less ideal.
"Although the study does not rule out the role of carbonaceous chondrites or other sources for the Earth's water, we show that the Earth's building blocks [ingredients] did contain significant water," Dr Laurette Piani, from Centre de Recherches Petrographiques et Geochimiques (CPRG), tells MEA WorldWide (MEAWW). "Their contribution to the Earth's water budget is probably far from being negligible," adds Dr Piani, the lead author of the study.
Simple theory on water's origins
In this study, Dr Piani and her colleagues gathered Enstatite chondrites from national museum collections of meteorites, including those at Field Museum in Chicago, USA. After removing materials that have been contaminated by Earth's water, they measure the amount of water and isotopic compositions in them.
These space rocks contained an unexpectedly high abundance of water. Enstatite chondrites and our planet essentially have a similar chemical makeup. "Their isotope compositions of many elements indicate a clear link with the Earth building blocks [ingredients]," explains Dr Piani. Further, they have similar oxygen, titanium, and calcium isotopes as our planet.
"If enstatite chondrites were effectively the building blocks of our planet — as strongly suggested by their similar isotopic compositions — this result implies that these types of chondrites supplied enough water to Earth to explain the origin of Earth's water, which is amazing!" says Dr Lionel Vacher, a postdoctoral researcher in physics in Arts & Sciences at Washington University in St. Louis who is a part of the research team.
The findings have raised a crucial question: how did Earth manage to incorporate water during its chaotic formation? According to Dr Peslier of NASA, the early solar system was a very violent place due to collisions which eventually gave rise to rocky planets. Large impacts could have resulted in the loss of water, she adds.
Besides, there is another puzzle the team is hoping to solve: understanding how Enstatite chondrites, which formed close to the sun, harbor volatile [evaporative] elements like hydrogen. "We are now starting some experimental works to go further on this." The theory proposed by Dr Piani and her colleagues is simple. "It simpler to have water come from in situ (from the zone in the proto-planetary disk where Earth form), than to invoke complicated scenarios of bringing material from the outer solar system," adds Dr Peslier. The study is published in Science.