The team also used the decay of uranium and lead isotopes (elements with the same number of protons but a different number of neutrons) to estimate the age of the titanite. (Because these elements decay at different rates, the ratio of the two can reveal the age of the rock.)
The tiny trace fossils were formed between 2.9 billion and 2.8 billion years ago, so they're about 650 million years younger than the formation as a whole.
The team also used a mathematical model of the cooling conditions in nearby pillow lava and found that the titanite structures were likely formed by the prevailing conditions in the cooling rock at that time.
About 2.9 billion years ago, magma intruded into the even more ancient rock and heated it up, forming the titanite structures as it cooled, the team thinks.
These findings discount the notion that the trace fossils were formed by primitive microbes at the dawn of life on Earth, the researchers argue.
"These textures are not biological or related to microbial activity," Grosch said.
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