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Chapter 19: Problem 66

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

Short Answer

Expert verified
Scientists are able to tell the age of fossils using a method called radiometric dating, more often through carbon dating. They measure the amount of carbon-14, a specific radioactive isotope in the fossil. Since carbon-14 decays over time, by measuring how much of it is left, they can estimate how long ago the organism died.

Step by step solution

01

Understanding Fossils

Firstly, it is crucial to know what fossils are. They are the preserved remains or traces of animals, plants, and other organisms from the past. Fossils form when organisms die and are buried in sediment. Over many years, the sediment turns into rock, preserving the shape of the organism.
02

Radiometric Dating

Secondly, we should understand the process of radiometric dating. Radiometric dating is a method where scientists look at the amount of certain isotopes that are left in a sample. All living organisms take up carbon from their environment including a specific amount of radioactive carbon-14. When the organism dies, the radioactive carbon-14 (t1/2 = 5730 years) in the dead tissue decays into nitrogen-14 over the years.
03

Carbon Dating

Thirdly, to estimate the age of the fossil, scientists measure the amount of carbon-14 left in the fossil's specimen. Because half-life of carbon-14 is known, by determining the amount of carbon-14 left in the fossil, the time since the organism died can be estimated. This method is known as carbon dating.
04

Limits of Carbon Dating

Lastly, carbon dating would only be effective for fossils that are less than 60,000 years old. This is due to the fact that very little carbon-14 remains in fossils older than this. For older fossils, other methods like dating the rocks around the fossil or using index fossils are used.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Fossils
Fossils give us a glimpse into the distant past. They are the remnants or traces of ancient organisms preserved in layers of sedimentary rock. These remains can be as simple as a leaf impression or as complex as an entire skeleton. Fossils are formed in several steps:
  • First, an organism dies and is buried quickly, often under water. This rapid burial helps preserve it from scavengers.
  • Over time, layers of sediment cover the fossil, and minerals seep into the remains, replacing the organic material cell by cell. This process is called "permineralization."
  • The sediments eventually harden into rock, encasing the fossil and preserving its form over millions of years.
By studying fossils, scientists can learn about the history of life on Earth and how different species have evolved.
Carbon Dating
Carbon dating, also known as radiocarbon dating, is a vital tool in determining the age of fossils. It focuses on a specific isotope, carbon-14, which is present in all living organisms. Here's how it works:
  • Living organisms absorb carbon from their environment, including carbon-14, an unstable isotope.
  • When the organism dies, it stops taking in carbon, and the carbon-14 within it begins to decay into nitrogen-14 at a known rate, which is called its "half-life." For carbon-14, this half-life is 5730 years.
  • Scientists can measure the remaining amount of carbon-14 in a sample to estimate how long it has been since the organism's death.
Carbon dating is extremely useful for dating relatively recent fossils, up to about 60,000 years old. Beyond this timeframe, the remaining carbon-14 is minimal and less reliable for accurate dating.
Isotopes
Isotopes are different forms of the same element with the same number of protons but a different number of neutrons. This gives them different atomic masses but the same chemical properties. In the context of radiometric dating:
  • Carbon-14 and nitrogen-14 are examples of isotopes. Carbon-14 is radioactive while nitrogen-14 is not.
  • When carbon-14 decays, it turns into nitrogen-14, releasing beta particles in the process.
  • Because isotopes like carbon-14 have predictable decay patterns, they are very useful in dating organisms and objects.
Different isotopes can be used to date different types of materials, providing a wide range of tools for scientists to study the ancient past. They allow for understanding not just the age of fossils but also geological formations, helping create an accurate timeline of Earth's history.

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Most popular questions from this chapter

A freshly isolated sample of \({ }^{90} \mathrm{Y}\) was found to have an activity of \(9.8 \times 10^{5}\) disintegrations per minute at 1: 00 P.M. on December 3,2003 . At 2: 15 P.M. on December \(17,2003,\) its activity was redetermined and found to be \(2.6 \times 10^{4}\) disintegrations per minute. Calculate the half-life of \({ }^{90} \mathrm{Y}\).

What are the steps in balancing nuclear equations?

A long-cherished dream of alchemists was to produce gold from cheaper and more abundant elements. This dream was finally realized when \({ }_{80}^{198} \mathrm{Hg}\) was converted into gold by neutron bombardment. Write a balanced equation for this reaction.

As of \(2011,\) elements 113 through 118 have all been synthesized. Element 113 (Uut) was formed by the alpha decay of element 115 (Uup); element 114 (Uuq) was created by bombarding \({ }^{244} \mathrm{Pu}\) with \({ }^{48} \mathrm{Ca}\); element 115 (Uup) was created by bombarding \({ }^{243} \mathrm{Am}\) with \({ }^{48} \mathrm{Ca}\); element 116 (Uuh) was created by bombarding \({ }^{248} \mathrm{Cm}\) with \({ }^{48} \mathrm{Ca}\); element 117 (Uus) was created by bombarding \({ }^{249} \mathrm{Bk}\) with \({ }^{48} \mathrm{Ca} ;\) element 118 (Uuo) was created by bombarding \({ }^{249} \mathrm{Cf}\) with \({ }^{48} \mathrm{Ca}\). Write an equation for each synthesis. Predict the chemical properties of these elements. (Before transuranium elements are given proper names, they are temporarily assigned three-letter symbols all starting with U.)

The constituents of wine contain, among others, carbon, hydrogen, and oxygen atoms. A bottle of wine was sealed about 6 yr ago. To confirm its age, which of the isotopes would you choose in a radioactive dating study? The half-lives of the isotopes are \({ }^{13} \mathrm{C}: 5730 \mathrm{yr} ;{ }^{15} \mathrm{O}: 124 \mathrm{~s} ;{ }^{3} \mathrm{H}: 12.5 \mathrm{yr} .\) Assume that the activities of the isotopes were known at the time the bottle was sealed.
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