http://edition.cnn.com/2014/02/24/world/oldest-earth-fragment/index.html?iid=article_sidebar
From a sheep ranch in Western Australia comes the oldest slice of Earth we know.
Scientists say they have dated an ancient crystal called a zircon to about 4.4 billion years, making it the earliest confirmed piece of the planet’s crust. The findings — the first to describe the zircon — were published in the journal Nature Geoscience on Sunday.
“This is the oldest and the best dated of all the crystals that have been reported,” said John Valley, lead study author and professor in the Department of Geoscience at the University of Wisconsin-Madison.
This crystal is a translucent red, Valley said, but glows blue when bombarded with electrons. At 400 micrometers long, its biggest dimension is just a tad larger than a house dust mite, or about four human hairs.
The crystal was found in an arid region north of Perth, Australia, in a low range of hills called the Jack Hills, in 2001.
Scientists say the crystal’s chemistry — specifically, the ratio of oxygen isotopes within it — suggests that the temperatures on Earth 4.4 billion years ago would have supported liquid water, and therefore perhaps life. Two isotopes of an element are considered different if they contain different numbers of neutrons.