Back in 2007, a team of researchers said they'd found 4.3-billion-year-old diamonds inside zircon crystals taken from Australia's Jack Hills. But those researchers had used a grinding paste made of synthetic diamonds to polish the zircons in preparation for lab tests ... and now a different team of scientists has discovered the so-called "diamonds" are actually just fragments of that polishing grit that got pushed into tiny cracks, LiveScience reports. The first team of researchers agrees with the conclusion, but insists there might still be ancient diamonds deeper inside the zircon; the second team of researchers—and some other experts—say that's extremely unlikely.
The "diamonds" were considered to be important evidence of a cooler early Earth, and early continents—their existence required "a radical revision of early Earth history," according to science blog azom.com. Most models suggest Earth was covered with lava during the Hadean era (its first 500 million years) and extremely hot. The "diamonds" suggested, though, that Earth was actually cool enough at the surface to crystallize the rock under which they supposedly formed; they also suggested that plate tectonics was already in motion, since pressure would have been necessary to form diamonds. But some scientists were always suspicious, especially considering the "diamonds" found in just one zircon ranged in age by more than a billion years. (Read more diamonds stories.)