University of Wisconsin-Madison geologist Professor John Valley said Zircons, the oldest known materials on Earth, offer a window in time back as far as 4.4 billion years ago. Because the crystals are exceptionally resistant to chemical changes, Valley said they are now used to determine the age of ancient rocks.

Valley previously used zircon grains to show rocky continents and liquid water formed on the Earth much earlier than previously thought, about 4.2 billion years ago.

Now a new study by UW-Madison geologists Takayuki Ushikubo, Noriko Kita and Valley shows rocky continents and liquid water existed at least 4.3 billion years ago and were subjected to heavy weathering by an acrid climate.

Ushikubo said atmospheric weathering could provide an answer to a long-standing question in geology: why no rock samples have ever been found dating to the first 500 million years after the Earth formed.

The research is detailed in the journal Earth and Planetary Science Letters.