Sulfur’s Role in Earth’s Water Formation: A Paradigm Shift in Planetary Science
A groundbreaking study has revealed that sulfur, a chemical element not present in H2O, played a crucial role in Earth’s initial water formation. This discovery supports a similar claim made the previous year, suggesting that our planet was inherently equipped to generate its own water rather than relying on external sources.
Water is fundamental to life on Earth, yet the planet formed in a region around the nascent sun so intensely hot that it should have been devoid of water. However, two independent studies of enstatite chondrites, a type of rare meteorite, have found substantial amounts of hydrogen, a key water component, bonded with sulfur. This bond allowed hydrogen to withstand the scorching heat and later combine with oxygen, Earth’s most abundant crustal element, to form water.
Alessandro Morbidelli, a planetary scientist at the Côte d’Azur Observatory in Nice, France, praised the synergy between the two studies, stating, “These two papers reinforce each other tremendously, and I think their story is becoming really compelling.”
The four inner planets—Mercury, Venus, Earth, and Mars—originated in the solar nebula’s inner region, a dense area of gas and dust orbiting the young sun. The friction within this region generated extreme heat, ostensibly eliminating water. Consequently, many scientists theorized that Earth’s water came from ice-bearing asteroids and comets from the outer solar system.
However, in 2020, a surprising discovery was made: enstatite chondrites contained hydrogen, indicating that Earth’s building blocks might have had hydrogen from the outset. This finding by cosmochemist Laurette Piani of the University of Lorraine in France and her colleagues suggested that hydrogen was part of Earth’s initial composition. Nonetheless, some scientists were skeptical, suspecting contemporary Earth’s water had contaminated the meteorites.
The following year, French researchers identified that the hydrogen in enstatite chondrites was bonded to sulfur. Recently, another research team found that most hydrogen in these meteorites is contained within pyrrhotite, an iron sulfide mineral. Thomas Barrett of the University of Oxford and his team reported this in a paper submitted to arXiv.org on June 19. UCLA cosmochemist Edward Young affirmed the findings, noting, “Their arguments about the spectroscopic characterization of where the hydrogen is living in the rock are good,” confirming the hydrogen’s native origin in the meteorite.
Morbidelli acknowledged this as a paradigm shift, stating, “You don’t accrete water. You accrete hydrogen and oxygen separately in different minerals, and then they combine with each other.” Early Earth’s hot and molten state, characterized by a magma ocean rich in oxygen, facilitated this process.
Nevertheless, Young posits that Earth’s water hydrogen might also have originated directly from the solar nebula’s molecular hydrogen gas, and additional water likely arrived from icy objects impacting Earth.
This discovery has profound implications for exobiology. As sulfur is the tenth most abundant element in the cosmos, rocky planets in other solar systems, even without icy asteroids and comets, could potentially acquire hydrogen and transform it into water. This capability could set the stage for life to develop on these worlds, underscoring sulfur’s pivotal role in the cosmic recipe for water and life.
