10.2 Rates of Nuclear Decay

A well-known theory is that early Americans were people from Siberia who crossed the Bering Strait into Alaska about 13,000 years ago. However, this theory has been challenged by recent scientific discoveries. In the 1990s, archaeologists working at a site in Cactus Hill, Virginia, found stone tools, charcoal, and animal bones that were at least 15,000 years old. Some of the artifacts were as much as 17,000 years old. The age of these artifacts suggests that the first Americans reached the continent much earlier than formerly thought. Some archaeologists have since revised their theories on the origin of America's earliest ancestors. One possible explanation is that the first Americans were people from Europe who crossed the Atlantic Ocean by using boats.

Figure 8 shows some of the artifacts from the Cactus Hill site. They certainly look very old, but the archaeologists needed to find out how old. One clue that can reveal the age of an object is how many radioactive nuclei it contains. Because most materials contain at least trace amounts of radioisotopes, scientists can estimate how old they are based on rates of nuclear decay.

Figure 8 These stone tools from the archaeological site in Cactus Hill, Virginia, are at least 15,000 years old. Scientists estimated the age of the site based on rates of nuclear decay.

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