Meteorites have revealed the likely distant origin of Earth’s volatile chemicals, some of which serve as building blocks for life. The researchers discovered that roughly half of the volatile element zinc on Earth came from asteroids originating in the outer solar system — the region beyond the asteroid belt that includes the planets Jupiter, Saturn, and Uranus.
Other important volatiles, such as water, are also expected to have been supplied by this region. Volatiles are elements or compounds that change from solid or liquid state into vapor at relatively low temperatures.
They include water and the six most common elements found in living organisms. As a result, the presence of this material was critical to the emergence of life on Earth.
Volatile Chemical Inventory
Previously, scientists believed that the majority of Earth’s volatiles came from asteroids that formed closer to the Earth. The findings provide important insights into how Earth came to have the unique conditions required for life to thrive.
“Our data show that about half of Earth’s zinc inventory was delivered by material from the outer solar system, beyond the orbit of Jupiter. Based on current models of early solar system development, this was completely unexpected,”
said senior author Professor Mark Rehkämper, of Imperial College London’s Department of Earth Science and Engineering.
This contribution of material from the outer solar system was critical in establishing the Earth’s inventory of volatile chemicals.
“It looks as though without the contribution of outer solar system material, the Earth would have a much lower amount of volatiles than we know it today, making it drier and potentially unable to nourish and sustain life,”
The researchers examined eleven meteorites from the inner solar system, known as non-carbonaceous meteorites, and seven meteorites from the outer solar system, known as carbonaceous meteorites, to conduct the study.
The relative abundances of the five distinct zinc forms, or isotopes, were calculated for each meteorite. The amount that each of these materials contributed to the Earth’s zinc inventory was then calculated by comparing each isotopic fingerprint with samples from the planet.
The findings indicate that although carbonaceous bodies only made up about 10% of the Earth’s mass, they provided about 50% of the planet’s zinc.
Zinc In Moon Rocks Next
According to the researchers, material with a high concentration of zinc and other volatile elements is likely to be relatively abundant in water as well, providing information about the source of Earth’s water.
“We’ve long known that some carbonaceous material was added to the Earth, but our findings suggest that this material played a key role in establishing our budget of volatile elements, some of which are essential for life to flourish,”
said first author Rayssa Martins, Ph.D. candidate at the Department of Earth Science and Engineering.
The researchers will next examine rocks from Mars and the moon, which once had water but has since dried up.
“The widely held theory is that the moon formed when a huge asteroid smashed into an embryonic Earth about 4.5 billion years ago. Analyzing zinc isotopes in moon rocks will help us to test this hypothesis and determine whether the colliding asteroid played an important part in delivering volatiles, including water, to the Earth,”
Professor Rehkämper said.
Reference: Rayssa Martins et al, Nucleosynthetic isotope anomalies of zinc in meteorites constrain the origin of Earth’s volatiles, Science (2023). Vol 379, Issue 6630 DOI: 10.1126/science.abn1021