I read a nice article today in Scientific American on the Jack Hills' zircons. These small crystals are the oldest bits of Earth known and have been dated to 4.4 Ga (Ga=Giga Annum=1 Billion Years). The discovery of the zircons was made by a team lead by John W Valley at the UW Madison Geology department. Read the complete story at the website: "The Earliest Piece of Earth"

The attached placemark will take you to the place of it's discovery, and contains two geologic overlays extracted from the 2005 paper by Cavosie and others.

Jack Hills Australia

Outcrop of the oldest known sample of the Earth, a 4.4 Ga detrital zircon (sample W74) in the Jack Hills metaconglomerate, Eranondoo Hill, Jack Hills, Western Australia. From l to r: John Valley, University of Wisconsin-Madison; Aaron Cavosie, University of Wisconsin-Madison; Simon Wilde, Curtin University.

Outcrop of the oldest known sample of the Earth

The oldest mineral yet discovered is a spec of zircon (tagged W74/2-36) found near this placemark. The U-Pb age of 4.4 billion years was determined by ion microprobe from the spot shown below.

4.4 Ga detrital zircon (sample W74)

This small (notice the scale bar) zircon apparently eroded out of the initial crust of the Earth and was transported here much later. Oxygen isotope analysis indicates that it may be have formed from wet oceanic sediments.

Here is a nice timeline from the UW showing the relative age of 4.4 Ga.