First we had a link to the oldest living thing on Earth [Botany Photo of the Day and the Oldest Living Organism] and now we link to the oldest thing on Earth [Oldest Rocks on Earth Discovered?].
These rocks are found in the Nuvvuagittuq region of Hudson Bay in Northwestern Quebec (Canada). As part of the Canadian shield they have long been known to be among the oldest rocks on Earth. Some of the rocks from this region have now been reliably dated to 4.28 billion years ago making them the oldest rocks known.
The dating technology is based on the decay of samarium to neodymium-142 and the work is published in this week's Science magazine (O'Neil et al. 2008).
These rocks are not the oldest things, however, because there are zircon inclusions from rocks in Western Australia that date back to 4.38 billion years. The zircon crystals probably formed somewhere else and were incorporated into the Australian rocks.
The Canadian rocks might also be much younger, having incorporated bits of older sediment, but for now, it looks like the Canadian shield may actually have formed over four billion years ago.
One thing is clear, Canada and Australia are the oldest countries in the world, by far.
J. O'Neil, R. W. Carlson, D. Francis, R. K. Stevenson (2008). Neodymium-142 Evidence for Hadean Mafic Crust Science, 321 (5897), 1828-1831 DOI: 10.1126/science.1161925