Wilde, another researcher, had been interested in ancient zircon crystals for a long time. "I asked Simon if he had any of the 4.1 billion-year-old zircons that had been reported from western Australia," he said.

Wilde replied that he didn't have any that had been dated, but he had the sample they came from and thought he could locate another.

He provided several tiny crystals from a conglomerate sample. A determination of their ages showed most were 4.1 billion years old, while one was dated to 4.4 billion years.

Wilde sent zircon samples encased in epoxy. Peck and Valley took them to Edinburgh, Scotland, where they used an Ion Microprobe to measure the oxygen isotope ratios in the minute crystals.

"We discovered that the oxygen isotope ratio was distinctly different from what we expected, and indicative of a low-temperature prehistory of the zircons." By prehistory, he meant the material that was present before the igneous rock melted.

"That was a total shock. We never expected this."

The ratios "meant liquid water" was present. To be liquid, it had to be below the boiling point — that is, not from the scorching Hadean period.

Of the five samples the researchers had, three had elevated isotope values, meaning formation when water was present. Since then, nearly 200 ancient zircon crystals have been analyzed "and many of them have these elevated oxygen isotope ratios."

Conditions under which life could have survived, Valley said, "existed at 4.2 billion years ago."

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