In the last few years, scientists have discovered that the early Earth cooled much faster than had been believed earlier, a finding that could affect our understanding of how quickly life appeared.

John W. Valley, professor of geology and geophysics at the University of Wisconsin, Madison, will speak on discoveries by himself and others, Wednesday at the Frontiers of Science Lecture, University of Utah. The free public talk will begin at 7:30 p.m. in the Aline Wilmot Skaggs Biology Building Auditorium.

Earth formed about 4.5 billion years ago as the solar system was condensing from interstellar gases, according to a press release from the University of Utah. At first "it was an inferno of boiling metals, minerals and gases.

"Red-hot oceans of molten rock, massive meteorite strikes and even brimstone in the atmosphere justify calling this time period the Hadean." The word refers to Hades, a biblical term for the underworld.

Before life could appear, the atmosphere had to cool enough for liquid water to form. The question is when that happened.

The earliest known fossils are dated in deposits from 3.5 billion years ago, the release adds. Earlier evidence from geology "placed the boundary between the Hadean and the subsequent Archean Eon at about 3.8 billion years ago."

Now Valley and colleagues have pushed back the era when the environment was cool enough for life by nearly half a billion years.

"Life could have formed 400 million years earlier than we thought previously," Valley said in a telephone interview from his home in Wisconsin.

The discovery was made by examining zircon crystals from western Australia, dating to 4.1 billion and 4.4 billion years old. This is a highly stable mineral, retaining elements from the time it formed in molten rock.

Although that rock was itself exceptionally hot, it was formed of matter that had cooled earlier, and the record of the cooling is retained in such information as the ratio of certain oxygen ions.

"I've been interested in ions for about 12 years, from all different ages and different localities from around the Earth," Valley said. He and a then-graduate student, William Peck (now an assistant professor at Colgate University, Hamilton, N.Y.), "hypothesized it would be interesting to analyze the oxygen isotope ratio of the oldest oxygen we could find on earth."

These ratios provide information about the temperature at which minerals formed.

"I had attempted several times to get old zircons from people, with no success," until a "very serendipitous meeting" at a conference in Beijing in 1998, where he met Simon Wilde.

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.