Determining exact age of rocks

Determining Absolute Age

Presentation made by T. Bart

Absolute age is the exact age of something, like a rock or fossil, in years. It helps scientists know how long ago things happened on Earth.

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What is Absolute Age?

Multiple Choice

What does absolute age tell scientists?

• Absolute age provides a comparison of different rock layers.
• Absolute age tells scientists the actual age of geological materials in years.
• Absolute age indicates the temperature of geological materials.
• Absolute age reveals the color of geological materials.

Erosion (when rocks break down) and deposition (when rocks build up) help scientists guess the age of things. But it only works for things made in the last 10,000-20,000 years because erosion and deposition can change over time.

Erosion and Deposition Rates

Multiple Choice

Why are erosion and deposition rates not always good for finding age?

• Erosion and deposition rates are the only methods used to determine geological age.
• Erosion and deposition rates are inconsistent and influenced by various factors, making them unreliable for age determination.
• Erosion and deposition rates can be measured precisely without any external influences.
• Erosion and deposition rates are always consistent and reliable for age determination.

A varve is a layer of rock that forms each year in lakes. In summer, a thick layer forms, and in winter, a thin layer forms. Counting varves tells us how many years have passed.

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What are Varves?

Multiple Choice

What does each varve layer show?

• Each varve layer shows daily temperature changes.
• Each varve layer shows geological age of rocks.
• Each varve layer shows monthly rainfall patterns.
• Each varve layer shows annual sediment deposition and seasonal variations.

Radiometric dating is a way to find the age of rocks using something called “half-life.” Half-life is the time it takes for half of a radioactive element to change into something else.

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Radiometric Dating and Half-Life

Multiple Choice

What is a half-life?

• The amount of time it takes for a substance to double in quantity.
• The time required for a substance to reach its maximum potency.
• The time it takes for half of a substance to decay or be eliminated.
• The period during which a substance becomes completely inert.

Scientists use different radioactive elements to find the age of different things:

• Uranium-238: Good for very old rocks (4.5 billion years)

• Potassium-40: Good for rocks up to billions of years old

• Carbon-14: Good for living things up to 70,000 years old

Different Radioactive Elements Used

Multiple Choice

Which element is best for finding the age of fossils?

• Oxygen-16
• Uranium-238
• Potassium-40
• Carbon-14

Carbon-14 is a kind of radioactive carbon that living things take in. When the plant or animal dies, Carbon-14 starts to change. Scientists measure how much Carbon-14 is left to find the age of the fossil.

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How Carbon-14 Dating Works

Multiple Choice

Carbon-14 dating is used for finding the age of:

• Living organisms, like plants and animals.
• Inorganic materials, such as metals.
• Geological formations, such as rocks.
• Organic materials, such as wood and bone.

In radiometric dating, a parent isotope is the original element. When it changes, it makes a new daughter isotope. By measuring how much parent and daughter isotope is in a rock, scientists can find the rock’s age.

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Parent and Daughter Isotopes

Multiple Choice

In radiometric dating, the parent isotope is:

• the stable isotope
• the decay product
• the non-radioactive element
• the original radioactive isotope

​Summary (1/2)

• Absolute Age - The exact age of rocks or fossils in years, helping scientists know how long ago things happened.

• Erosion & Deposition Rates - Erosion and deposition can help estimate the age of recent formations (up to 20,000 years) but are less reliable for older layers since rates can vary.

• Varves - Layers in lake sediments that form every year, with thicker summer layers and thinner winter layers. Counting varves shows how many years have passed.

​Summary (2/2)

• Radiometric Dating & Half-Life - Radiometric dating uses the “half-life” of radioactive elements, which is the time it takes for half of the element to decay into another form.

• Types of Radioactive Elements - Different elements are used to date materials of different ages. Carbon-14 is used for recent materials, while Uranium-238 is used for ancient rocks.

• Carbon-14 Dating - This method is used to date organic remains (like plants or animals) up to 70,000 years old by measuring the remaining Carbon-14.

• Parent and Daughter Isotopes - In radiometric dating, the original radioactive element (parent isotope) decays over time to form a stable product (daughter isotope), which helps scientists estimate age.

Any questions?

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