The success of a team that produced three-dimensional images of prehistoric embryos (see page 680) is down to the group's tenacity, says Philip Donoghue, an Earth scientist at the University of Bristol, UK.

The field caught the interest of another Earth scientist, Xi-Ping Dong of Peking University in China, during a visit to Harvard University in 1996. “He didn't discover these embryos by chance,” says Donoghue. “He saw presentations of other rare embryo finds, and wanted to find some himself. It got him thinking about biology rather than geology.”

Dong teamed up with Donoghue, who has expertise in scanning electron microscopy. They began by looking at conodonts — tiny eel-like creatures dating back 510 million years. By chance, Dong found embryos of a prehistoric segmented worm in his samples. He eventually processed 12 tonnes of rock into sand-like particles and found five embryos.

A 2004 paper then drew the attention of Marco Stampanoni at the Swiss Light Source near Zurich. He had developed a technique in 3D X-ray tomography that held promise for imaging the tiny fossils in great detail. Stampanoni invited Donoghue to Zurich and gave him 24 hours of beam time.

Donoghue, who never used to work on embryos, now devotes much of his time to them.