Zircon Crystal ]
The tiny gem is said to have formed 4.4 billion years ago University of Wisconsin-Madison

A tiny crystal extracted from sandstone in a sheep ranch in Australia is the oldest known piece of planet earth and dates back 4.4 billion years, scientists have confirmed.

Two different age-determining techniques were used to establish the age of the zircon crystal and found it was formed just 160 million years after the solar system was said to have come into existence.

The discovery also shed light on the formation of the Earth's crust and how soon it formed after the planet was formed.

John Valley, a University of Wisconsin geoscience professor who headed the research, said the discovery of the gem suggested that early Earth was not as inhospitable a place 4.5 billion years ago as believed.

The Earth's crust is said to have formed 100 million years after the Earth formed - significantly quicker than scientists thought.

Writing in the journal Nature Geoscience, Valley said the discovery of the tiny zircon fragment – which is just twice as thick as a human hair – supported the notion of a "cool early Earth" where temperatures were low enough for liquid water, oceans and a hydrosphere not long after the planet's crust formed from a sea of molten rock.

Zircon Crystal
A timeline of earth's formation places the zircon duirng a "cool early Earth" 4.4 billion years ago University of Wisconsin-Madison

This period of Earth's formation is known as the Hadean eon - named after the ancient Greek god of the underworld, Hades - because of its apparently hellish conditions of extreme heat and relentless meteorite bombardment.

"The study reinforces our conclusion that Earth had a hydrosphere before 4.3 billion years ago," said Valley.

The research also suggested the planet could have also sustained life earlier than previously understood.

"One of the things that we're really interested in is when did the Earth first become habitable for life? When did it cool off enough that life might have emerged?" Valley said.

"We have no evidence that life existed then. We have no evidence that it didn't. But there is no reason why life could not have existed on Earth 4.3 billion years ago," he added.

The zircon was extracted in 2001 from a rock in from the Jack Hills region in Western Australia, an area known to contain some of the oldest pieces of the planet's crust.