Today, archaeologists uncover the past, layer by layer. Objects can be dated by the radiocarbon method (measuring the amount of radioactive carbon-14 left in charcoal, wood or animal bones). The study of tree growth-rings also helps them, especially using the wood of the bristle cone pine of California. This is the oldest living thing on Earth, reaching ages of up to 4600 years. Tree-ring dating has helped to correct errors in radiocarbon dates.
