The thin shell of the oxygen atmosphere on earth keeps us alive, although we still don’t know exactly how it was formed. A new study from the University of Chicago reveals clues about the role iron had to play. (This image is a sunrise captured by the International Space Station.) Photo credit: NASA
Innovative technology analyzes ancient rocks to understand the role of iron.
For much of the earth’s four and a half billion years, the planet was barren and inhospitable; It was only when the world got its oxygen blanket that multicellular life could really get going. But scientists are still trying to understand exactly how – and why – our planet has this beautifully oxygenated atmosphere.
“If you think about it, this is the most important change our planet has seen in its life and we are still not sure exactly how it happened,” said Nicolas Dauphas, the Louis Block professor of geophysical sciences of the University of Chicago. “Any advance you can make in answering this question is really important.”
In a new study published on October 23, 2020, in scienceUChicago graduate student Andy Heard, Dauphas, and their colleagues used a groundbreaking technique to uncover new information about the role of oceanic iron in the rise of the Earth’s atmosphere. The results reveal more about the Earth’s history and may even shed light on finding habitable planets in other star systems.
Scientists have carefully created an ancient earth timeline by analyzing very ancient rocks. The chemical composition of such rocks changes depending on the conditions under which they were formed.
“The interesting thing is that before the permanent great oxygenation event that happened 2.4 billion years ago, there is evidence in the timeline of those tempting little bursts of oxygen that seem like Earth was trying to set the stage for to create that atmosphere, “said Heard, the paper’s first author.” But the methods available were not precise enough to work out the information needed. ”
This is the most important change our planet has seen in its life and we are still not sure how exactly it happened. “
– – Prof. Nicolas Dauphas
It all comes down to a riddle.
As bridge engineers and car owners know, oxygen and iron rust when water is around. “In the early days, the oceans were full of iron, which could gobble up any free oxygen that hung around,” Heard said. In theory, rust formation should consume excess oxygen and not create an atmosphere.
Heard and Dauphas wanted to test a way to explain how oxygen could have accumulated despite this obvious problem: they knew that some of the iron in the oceans actually combined with sulfur from volcanoes to form pyrite (better known as fool’s gold). This process actually releases oxygen in The atmosphere. The question was which of these processes “wins”.
To test this, Heard used state-of-the-art facilities at Dauphas’ Origins Lab to develop a rigorous new technique for measuring tiny variations in iron isotopes to find out which path the iron took. Working with world experts from the University of Edinburgh, he also needed to develop a more thorough understanding of how the iron-pyrite pathway works. (“To make sulfide and conduct these experiments, colleagues need to understand that laboratories smell like rotten eggs,” Heard said.) Then the scientists used the technique to analyze rocks that were 2.6 to 2.3 billion years old Australia and South Africa.
Their analysis found that even in oceans that should have been rusting a lot of oxygen, certain conditions may have encouraged the formation of enough pyrite for oxygen to escape from the water and possibly form an atmosphere.
“It’s a complicated problem with lots of moving parts, but we were able to fix part of it,” said Dauphas.
“Progress on such a huge problem is really valuable to the community,” said Heard. “Especially when we’re looking for exoplanets, we really need to understand every detail of how our own earth became habitable.”
As telescopes search the skies for other planets and find thousands, scientists need to narrow down for more information on potential life. By learning more about the ways in which the earth became habitable, they can look for evidence of similar processes on other planets.
“I like to think that before the rise in oxygen, Earth is the best laboratory for understanding exoplanets,” said Heard.
Reference: “Triple Iron Isotope Restrictions on the Role of Ocean Iron Sinks in Early Oxygen Supply to the Atmosphere” by Andy W. Heard, Nicolas Dauphas, Romain Guilbaud, Olivier J. Rouxel, Ian B. Butler, Nicole X. Nie, and Andrey Bekker, Jan. October 2020, science.
DOI: 10.1126 / science.aaz8821
