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Clues from some unusual Arizona rocks pointed Rice University scientists toward a discovery—a subtle chemical signature in rocks the world over—that could answer a long-standing mystery: What stole the iron from Earth's continents?
The find has weighty implications. If the iron content of continental rocks was a bit greater, as it is in the rocks beneath Earth's oceans, for example, our atmosphere might look more like that of Mars, a planet so littered with rusty, oxidized rocks that it appears red even from Earth.
Paper - Online - Science - Advances - Rice
In a new paper available online in Science Advances, Rice petrologists Cin-Ty Lee, Ming Tang, Monica Erdman and Graham Eldridge make a case that garnet steals the most iron from continents. The hypothesis flies in the face of 40-plus years of geophysical thinking, and Tang, a postdoctoral fellow, and Lee, professor and chair of the Department of Earth, Environmental and Planetary Sciences at Rice, said they expect a healthy dose of skepticism from peers.
"The standard view, which even we agreed with and wrote papers agreeing with, is that iron is removed from continental crust by another mineral called magnetite," Lee said. "I think people haven't thought much about garnet, possibly because it doesn't show up very much and magnetite shows up in a lot of samples."
Case - Mineral - Iron - Disappears - Miles
Building a case for or against either mineral isn't easy because the iron they're accused of stealing disappears many miles below active volcanoes. The prime example today is the arc of volcanoes that span the Andes Mountains in South America. Similar continental arcs are believed to have formed much of Earth's major landmasses, but scientists have no instruments capable of directly observing what happens beneath continental volcanic arcs. Instead, the missing iron mystery must be solved with deductive reasoning about Earth's inner workings and rare rocks that hold clues from the scene of...
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