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Forces For Change DATING FOSSILS To find out what happened millions of years ago archaeologists have to recover, analyse and date ancient fossils and tools. Fossils are formed when animal or plant remains are trapped between layers of rock. When the rock is broken open, an imprint is revealed. Since the 1940's researchers have used radiocarbon (Carbon-14) techniques to date fossils. What happens is the following: living animals and plants absorb tiny amounts of carbon from the atmosphere. When they die, the carbon declines at a slow, measurable rate. By finding out how much carbon there is in the fossil, researchers can make an approximate guess of the age. However, radio carbon dating is only accurate when testing fossils less than 100,000 years old. For anything older, tests need to be done on the surrounding rock and assumptions made about fossil ageing. Assessments can also be made by measuring the rate of potassium and uranium decay. Basically the deeper something is found, the older it is. DNA The study of DNA - the genetic blueprint found in all cells - has made a huge impact on the analysis of African history. Study of DNA and in particular mitochondria DNA (mtDNA), which is passed down the female line, has allowed scientists to reconstruct the past history of human populations. Each molecule of mtDNA carries a history of its lineage. It is through this genetic analysis that most scientists have concluded that modern man evolved in Africa and then spread throughout the rest of the world. Some geneticists have even argued that every woman alive today carries the mtDNA of just one African woman who lived 10,000 generations ago. |
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