New Worlds: A rusty green early ocean?

Their findings suggest that green rust was probably a major player in the iron cycle.

Weizmann Institute of Science (photo credit: MICHAEL JACOBSON/WIKIMEDIA COMMONS)
Weizmann Institute of Science
Though they may seem rock solid, the ancient sedimentary rocks called iron formations – the world’s chief economic source of iron ore – were once dissolved in seawater. Dr. Itay Halevy and his group in the Weizmann Institute of Science’s earth and planetary sciences department suggest that billions of years ago, the “rust” that formed in the seawater and sank to the ocean bed was green – an iron-based mineral that is rare on Earth today but might once have been relatively common.
It is known that there was dissolved iron in the early oceans, and this is a strong indication that Earth’s free oxygen concentrations were exceedingly low. Otherwise, the iron would have reacted with oxygen to form iron oxides, which are the rusty red deposits familiar to anyone who’s left a bike out in the rain. Today, said Halevy, iron is delivered from the land to the oceans as small insoluble oxide particles in rivers. But this mode of sedimentation only came about as free oxygen accumulated in Earth’s atmosphere, about 2.5 billion years ago. With almost no oxygen, the oceans were iron-rich, but that did not mean that iron remained dissolved in seawater indefinitely. It ultimately formed insoluble compounds with other elements and settled to the seabed to give rise to banded iron formations.
The idea that one of those insoluble compounds could be a rusty green mineral occurred to him during his doctoral research, when he was trying to recreate the conditions on early Mars, including its rusty-red iron sediments.
“I got some green stuff I didn’t recognize at first, which quickly turned orange when I exposed it to air. With a little more careful experimentation, I found that this was a mineral called green rust, which is extremely rare on Earth today, owing to its affinity for oxygen,” Halevy said. Today, green rust quickly transforms into the familiar red rust, but with not much free oxygen around, Halevy reasoned, it could have been an important way for dissolved iron to form solid compounds and settle to the sea floor.
Support for these ideas comes from Sulawesi, Indonesia, where green rust forms in iron-rich, oxygen-poor Lake Matano, thought to be similar to the seawater that existed during extended periods of Earth’s early history. To test his ideas in detail and explore their significance, Halevy and his team recreated the conditions of the ancient, oxygen-free, Precambrian ocean. They found that green rust not only forms under these conditions, but that when left to age, it transforms into the minerals found in Precambrian iron formations – a combination of iron-bearing oxides, carbonates and silicates.
Their findings suggest that green rust was probably a major player in the iron cycle. The iron in the green rust later transformed into the minerals we can now observe in the geologic record.
“Of course, it would have been one of several means of iron deposition, just as a number of different processes are involved in chemical sedimentation in the oceans today,” concluded Halevy. “But as far as we can tell, green rust should have delivered a substantial proportion of iron to the very early ocean sediments.”
Israeli teens competing against 1,800 peers in 75 countries received impressive honors at the recent international Intel ISEF Young Scientists Competition in Los Angeles. One of the 10 Israelis received third prize, while another won an honorable mention.
Gonen Zimmerman of the Levi Eshkol School in Ramat Hasharon School took third place for his research on “Orthonormal Polynomials with the Two-Dimensional Nevai Condition.” Zimmerman studied in a special program at the Hebrew University. He also received a $1,000 prize and honorable mention in a special ceremony held by the American Mathematical Society.
Zimmerman explained the abstruse subject by saying: “This is an open question in mathematics whose solution has great importance for mathematics and physics.”
In addition, Na’ama Schor of the High School for Environmental Education at the Sde Boker Midrasha received an honorable mention from the American Physiological Association for her research on “The Morality of ‘Larks’ and ‘Owls’: The Relationship between the Circadian Clock and Morality in Decision-Making.”
The 10 Israeli participants were the finalists in the Young Scientists Competition held for the 20th time at Jerusalem’s Bloomfield Science Museum in March.
The world competition is part of the research and development program of the European Union to encourage cooperation among young scientists In Europe and Israel and Intel-ISEF in the US. The Israeli competition is supported by the Goren-Monte-Ferrari Family in Italy via the Jerusalem Foundation and the Education Ministry.