Chapter 15, Problem 38A

Summary Introduction

To explain:

The importance of radiometric dating to paleontologists

Introduction:

A fossil is any preserved evidence of an organism. A paleontologist is a scientist who studies fossils. He or she records life left in rocks and from fossil evidence he or she infers the diet of the organism and the kind of environment in which it lived. Geologists noticed that layers of same age tended to have the same kind of fossils no matter where the rocks were found. This led to the establishment of relative age scale for rocks all over the world.

Answer to Problem 38A

Importance of radiometric dating includes:

• It helps to measure the age of rocks and fossils.
• Mummies can be dated using carbon -14 isotope.

Explanation of Solution

There are two methods of measuring the age of rocks: relative dating and radiometric dating.

Radiometric dating is used to measure the age of rock. It uses decay of radioactive isotopes to measure the age of rock. The method requires that the half- life of the isotope is known. The relative amounts of radioactive isotope and its decay product must also be known.

Uranium 238 is used to measure the age of rocks. Radioactive isotopes that can be used for radiometric dating are found only in igneous and metamorphic rocks, not in sedimentary rocks. So these isotopes cannot be used to date rocks containing fossils. However if igneous rocks are associated with sedimentary rocks that contain fossils, the isotopes can be used to date fossils. Carbon -14 is used to date organic substances such as bones and tissues. Hence they can be used to date mummies but not older than 60,000 years as carbon has a short half- life.