The Earth is old and it’s hard to tell exactly how old the Earth really is because rocks are constantly renewing themselves. When rocks are melted, the heat destroys the evidence used for radiometric dating, therefore, it conceals the Earth’s age. This video explains partially how the Earth is dated by measuring the ages of rocks in years through a process of using radioactive atoms. In conclusion, the Earth is older than what is known.

Why Watch This Video?

  1. Have you ever wondered how old the Earth is?
  2. Would you like to know how the Earth is measured and dated?
  3. Have you ever been confused by radiometric dating?

Key Terms

Radioactive decay: A process when the nucleus becomes unstable from radiation causing energy loss. The breakdown of the nucleus of an atom occurs and the atom then becomes a different element.

Metamorphic rocks (Metamorphose): Come from rocks that have existed and experienced change when they are exposed to intense heat and/or pressure, then become a new type of structure but do not melt.

Radiometric dating: Lets us find the actual age of a rock. Radiometric dating is a method that relies on known and consistent rates of decay of radioactive isotopes in order to find out how long a rock has been around.

Loose Ends

Some of Earth’s history is lost

The Earth is estimated to be 4.5 billion years old, but there are gaps in the rock record that make it harder to know the exact age. Layers of rock may be damaged and have disappeared and/or been replaced by other elements.

Parent and daughter isotopes

By measuring the ratio of parent and daughter isotopes (where the parent is the radioactive isotope and the daughter is the isotope it decays into), geologists can determine how long the radioactive isotopes in a rock sample have been going through decay. This method provides the age of the rock sample in years.

The work of dating rocks continues

It isn’t necessarily the case that the ages of rocks on Earth will be unknown indefinitely. Geologist continue to studying Earth’s rocks, and are working on new and improved methods for measuring the age of rocks in years. At the same time, what will not change is the order in which a rock occurs, which is important in Earth’s history.

Self-Test Questions

Scroll down to see the answers.

1. Why does the Earth look reasonably fresh and new?

  1. Broken down rock.
  2. Rocks weather on earth.
  3. Earths outer most layer is constantly renewing itself.
  4. Impacts of meteorites.

2. How are mountain belts formed?

  1. When continents collide.
  2.  When a volcano erupts.
  3. When rocks are weathered.
  4. Mountain belts have always existed.

3. What process can be measured to help us date rocks?

  1. Melting rocks
  2. Process of remaking rocks
  3. The way in which rocks spread
  4. Radioactive decay

4. What happens as Earth “remakes” its rocks that results in it being hard to measure the age of the rocks?

  1. Most of the Earth’s rocks lose the radioactive isotopes they once contained.
  2. It resets the built-in clocks, making it hard to look back into Earth’s history.
  3. The rocks get age faster as they are modified
  4. Isotopes in rocks decay at a slower rate than expected

5. When dating a rock with uranium and lead, the more lead you find in a rock, ____.

  1. the younger the rock.
  2. the older the rock.
  3. the more likely the rock has been recycled.
  4. the more likely the rock has been weathered.


1. Processes like volcanic eruptions constantly create new rocks.

2. Answer a is correct. When continents collide, new structures are created on Earth’s surface.

3. Answer d is correct. Isotopes release energy and/or particles- referred to as radiation- when they decay, so unstable isotopes are also called radioactive isotopes. Radiometric dating takes advantage of the fact that radioactive isotopes decay at a known rate.

4. Answer b is correct. When rocks are remade or recycled, it loses its radioactive evidence therefore making it harder to test the sample to properly date the rock.

5. The correct answer is b. Geologists test the zircon in rocks for an indication of how much lead is present to determine whether the rock is older or not.

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Item Credit: Minute Earth

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