A tiny zircon said to be 4.4 billion-year-old is the oldest known piece of Earth, as per new research. Geoscience Professor John Valley from the University of Wisconsin in the United States found the gem on an outback sheep station in Western Australia.

Prof. Valley said the size of the stone is so small that is hardly visible to a human eye. It is around the size of two human hair. While sharing about how he found the tiny gem, Prof. Valley said he was on a field trip to Jack Hills in 2001 when he found it.

Jack Hills is around 600 km north of Perth and is known to be a place for its ancient gem stones. The stone was assessed through two measures, atom-probe tomography and ion mass spectrometry. Both the measures confirmed the age of the stone.

After examining the stone, Prof. Valley said the gem was formed after the Earth had cooled to form a crust.

Though the stone might appear as a small fragment of crystal, it is very important in terms of science. The crystal is now being used by scientists to know about how Earth became habitable.

The rock assessment has unveiled the Earth's crust formed at least 4.4 billion years ago, which is just 160 million years after the formation of our solar system. Another thing revealed is Earth was not a harsh place.

"This may also help us understand how other habitable planets would form", said Prof. Valley. The study has been published in the journal Nature Geoscience. The study supports that the Earth had a hydrosphere before 4.3 billion years ago.