Meteorites reveal likely origin of Earth’s volatile chemicals

Newswise — By analyzing meteorites, Imperial researchers have discovered the probable remote origin of Earth’s volatile chemicals, some of which form the building blocks of life.

They found that about half of Earth’s inventory of the volatile element zinc came from asteroids that originated in the outer Solar System, the part beyond the asteroid belt that includes the planets Jupiter, Saturn and Uranus. This material is also expected to have supplied other important volatiles such as water.

Volatiles are elements or compounds that change from a solid or liquid to a vapor state at relatively low temperatures. They include the six most common elements found in living organisms, as well as water. As such, the addition of this material will have been important to the emergence of life on Earth.

Before this, researchers thought that most of Earth’s volatiles came from asteroids that formed closer to Earth. The findings reveal important clues about how Earth came to host the special conditions necessary to support life.

Lead author Professor Mark Rehkämper, from Imperial College London’s Department of Earth Sciences and Engineering, said: “Our data show that about half of Earth’s zinc inventory was delivered by material from the outer Solar System, more beyond the orbit of Jupiter. Based on current models of the early development of the Solar System, this was completely unexpected.”

Previous research suggested that Earth formed almost exclusively from material from the inner Solar System, which the researchers inferred was Earth’s predominant source of volatile chemicals. On the contrary, the new findings suggest that the outer Solar System played a bigger role than previously thought.

Professor Rehkämper added: “This contribution of material from the outer Solar System played a vital role in establishing Earth’s inventory of volatile chemicals. It appears that without the contribution of material from the outer Solar System, Earth would have far fewer volatiles than we know today, making it drier and potentially unable to nurture and support life.”

The findings are published today in Science.

To carry out the study, the researchers examined 18 meteorites of different origins: eleven from the inner Solar System, known as non-carbonaceous meteorites, and seven from the outer Solar System, known as carbonaceous meteorites.

For each meteorite they measured the relative abundances of the five different forms, or isotopes, of zinc. They then compared each isotopic fingerprint to samples from Earth to estimate how much each of these materials contributed to Earth’s zinc inventory. The results suggest that while Earth only incorporated about ten percent of its mass of carbonaceous bodies, this material supplied about half of Earth’s zinc.

The researchers say that material with a high concentration of zinc and other volatile components is also likely to be relatively abundant in water, giving clues to the origin of Earth’s water.

First author of the paper, Rayssa Martins, a PhD candidate in the Department of Earth Sciences and Engineering, said: “We have known for a long time that carbonaceous material was added to Earth, but our findings suggest that this material played a role key in establishing our budget for volatile elements, some of which are essential for life to flourish.”

Next, the researchers will analyze rocks from Mars, which held water 4.1 to 3 billion years ago before drying up, and the Moon. Professor Rehkämper said: “The widely held theory is that the Moon formed when a huge asteroid slammed into an embryonic Earth around 4.5 billion years ago. Analysis of zinc isotopes in lunar rocks will help us test this hypothesis and determine whether the colliding asteroid played a significant role in delivering volatiles, including water, to Earth.”

This work was funded by the Science and Technology Facilities Council (STFC, part of UKRI) and Rayssa Martins is funded by a Presidents’ PhD fellowship from Imperial College London.