John Valley, a geologist at University of Wisconsin in Madison who was not involved in this study, notes that there are four known "recipes" that create diamonds.
But the 4.25-billion-year-old diamonds "suggest the additional possibility that the diamonds have formed by some process that is not yet understood."
Study co-author Wilde said, "The bottom line is that we really honestly don't know why they're there."
The study, led by Martina Menneken, a master's student at the Westfaelische Wilhelms-Universitaet, appears in this week's issue of the journal Nature. Alexander Nemchin from Curtin University of Technology also contributed.
Clues to Earth's Earliest Life?
One exciting prospect is that if Earth cooled down earlier in its existence, then it's possible that life on Earth cropped up earlier too, Geisler said.
(Related: "Weird Australia Rocks Are Earliest Signs of Life, Study Says" [June 7, 2006].)
Geisler hopes that analyzing the various types of carbon in these diamonds could reveal whether this was the case.
"We don't know yet, but this is potential information contained in the carbon," he said.
Valley, the Wisconsin geologist, added, "Even though these diamonds are too small to be of commercial value as gems, scientists will find them even more valuable for the information they carry about the Earth."
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