Welcome to You Ask Andy

Daniel Jaterka, age 9, of Granger, Utah, for his question:

HOW IS THE AGE OF A FOSSIL DETERMINED?

Scientists learn a lot from studying fossils. They can piece together the history of life on earth by looking at rock samples. Shells found in rocks in the Alps, Himalayas, Rockies and Andes, for example, tell us that this land was once under water and that early in our history these areas were lifted up by earthquakes to form mountains.

A fossil is the record or remains of an animal or plant that lived in the past. Scientists estimate that the oldest known fossils are one celled algae or bacteria that lived more than 3 billion 100 million years ago. Plants and animals with hard shells and skeletons have been tracked back 600 million years.

Determination of a fossil's age is made by scientists who attempt to find out the age of the rock in which the specimen is found. They do this by checking the amounts of certain chemicals which are present to determine just how long they have been buried.

Paleontology is the science of the study of fossils. Experts in this field have found that most fossils were formed in sedimentary rocks  those that are built up in layers. The oldest fossils are found in the deepest layers. The order of the rock layers can give an indication of the order in which the animals developed.

To learn how long an animal lived, paleontologists must find out the age of the rocks. One way they do this is by studying the amount of radioactive elements in the rocks. Radiogeology, the science that deals with the relation of radioactivity to geology, comes in very handy here.

The earth, ocean water and even the air we breathe contains small amounts of radioactivity. This is something scientists can chart and record.

on the basis of the ratios of lead isotopes in ancient rocks and in meteorites, scientists estimate that the solar system and the earth itself are about 4 billion 500 million years old. This figure agrees with calculations based on the decay of radioactive material.

Radioactive uranium, as time passes, constantly disintegrates and finally becomes lead. Analysis of radiocarbon content makes it possible to find the age of such items as wood, bone and fossilized pollen. The age of various specimens lets scientists determine when certain things and once living creatures existed.

 

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