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Chapter 21: Problem 60

How are scientists able to tell the age of a fossil?

Short Answer

Expert verified
Scientists date fossils using two methods: relative and absolute dating. Relative dating, like stratigraphy, orders fossils from oldest to newest based on their layers in the earth. Absolute dating, like radiometric dating, provides a more precise age based on the half-life decay of radioactive elements, such as carbon-14, within the fossil.

Step by step solution

01

Introduction to Fossil Dating

Scientists utilize several methods to tell the age of a fossil. These methods can be classified into two groups: relative dating and absolute dating. Relative dating, as the name suggests, gives the relative age, meaning scientists know one event occurred before another but do not know how much earlier. Absolute dating, on the other hand, gives a more precise age in years.
02

Relative Dating - Stratigraphy

In relative dating, scientist use a method known as stratigraphy. Stratigraphy is a method of dating that is based on the law of superposition. This law states that older layers of rock are found below younger layers. So, if a fossil is found in one layer of rock, and a different fossil is found in another layer above it, then the fossil in the lower rock layer is considered older.
03

Absolute Dating - Radiometric Dating

Absolute dating utilizes a method known as radiometric dating. This is the most common method of dating fossils. Radioactive elements present in a rock decay at a constant rate, known as its half-life. By calculating the amount of decayed and undecayed elements in a sample (e.g., ratio of Carbon-14 to Carbon-12), the time elapsed since death of the organism can be determined.

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Most popular questions from this chapter

Fill in the blanks in these radioactive decay series: (a) \(^{232} \mathrm{Th} \stackrel{\alpha}{\longrightarrow}\) _______ \(\stackrel{\beta}{\longrightarrow}\) ________ \(\stackrel{\beta}{\longrightarrow}{ }^{228} \mathrm{Th}\) (b) \({ }^{235} \mathrm{U} \stackrel{\alpha}{\longrightarrow}\) ________ \(\stackrel{\beta}{\longrightarrow}\) _________ \(\stackrel{\alpha}{\longrightarrow}^{227} \mathrm{Ac}\) (c) _______ \(\stackrel{\alpha}{\longrightarrow}{ }^{233} \mathrm{~Pa} \stackrel{\beta}{\longrightarrow}\) ___________ \(\stackrel{\alpha}{\longrightarrow}\) ________.

To detect bombs that may be smuggled onto airplanes, the Federal Aviation Administration (FAA) will soon require all major airports in the United States to install thermal neutron analyzers. The thermal neutron analyzer will bombard baggage with low-energy neutrons, converting some of the nitrogen- 14 nuclei to nitrogen- \(15,\) with simultaneous emission of \(\gamma\) rays. Because nitrogen content is usually high in explosives, detection of a high dosage of \(\gamma\) rays will suggest that a bomb may be present. (a) Write an equation for the nuclear process. (b) Compare this technique with the conventional X-ray detection method.

The nucleus of nitrogen- 18 lies above the stability belt. Write an equation for a nuclear reaction by which nitrogen- 18 can achieve stability.

The radioactive decay of \(\mathrm{T} 1-206\) to \(\mathrm{Pb}-206\) has a half- life of 4.20 min. Starting with \(5.00 \times 10^{22}\) atoms of \(\mathrm{Tl}-206,\) calculate the number of such atoms left after 42.0 min.

Bismuth-214 is an \(\alpha\) -emitter with a half-life of 19.7 min. A 5.26 -mg sample of the isotope is placed in a sealed, evacuated flask of volume \(20.0 \mathrm{~mL}\) at \(40^{\circ} \mathrm{C}\). Assuming that all the \(\alpha\) particles generated are converted to helium gas and that the other decay product is nonradioactive, calculate the pressure (in \(\mathrm{mmHg}\) ) inside the flask after 78.8 min. Use 214 amu for the atomic mass of bismuth.
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