Dating Rocks

What is Absolute Age in the context of geology?

The actual age of a rock or fossil, determined through radioactive dating.

What is Radioactive Dating?

A method to measure the age of a rock or fossil by determining the decay of radioactive isotopes within it.

Which type of rock is considered the best for radiometric dating?

Igneous rocks are the best samples for radiometric dating.

What is Carbon-14 used for?

Carbon-14 is used to date living organisms and effective for dating organic materials up to about 50,000 years old.

What happens to the ratio of carbon-14 to carbon-12 after an organism dies?

The ratio begins to change as carbon-14 decays, allowing scientists to estimate the time of death.

Define Half-Life in the context of radioactive dating.

The time needed for half of a sample of a radioactive element to undergo decay and form daughter isotopes.

What does Relative Dating determine?

It determines the age of rock layers or fossils based on their positioning underground.

What does the Principle of Superposition state?

The oldest layer is on the bottom, and the youngest is on the top.

Explain the Principle of Original Horizontality.

Rocks and sediments are deposited horizontally; later forces may push and tilt them.

What is the Principle of Lateral Continuity?

Once sediments are deposited, erosion occurs over a large area but the layer beside remains the same age as before.

What does the Principle of Cross-Cutting Relationships state?

Igneous intrusions or faults are younger than the rock they cut across.

What does the Principle of Inclusions tell us?

Rock fragments in a layer are older than the layer itself.

What is a Bake Zone?

The area surrounding an igneous intrusion that has baked the rocks.

What does the principle of fossil succession state?

Fossil organisms succeed one another in a predetermined order, allowing time periods to be recognized by their fossil content.

What are Index Fossils?

Fossils that are widespread geographically, limited to a short span of geologic time, and occur in large numbers.

What are Unconformities in geology?

Surfaces representing geological time not accounted for in the rock record.

What is Disconformity?

A surface of erosion or nondeposition between beds parallel to one another.

Define Angular Unconformity.

An erosional surface on tilted or folded strata over which younger strata are deposited.

What characterizes Nonconformity?

An erosional surface cut into igneous or metamorphic rocks, overlain by sedimentary rocks.