Geology Study Guide: Relative Dating, Fossils, Radiometric Dating, and Geologic Time

These flashcards cover key concepts related to geology, including relative dating principles, fossils, radiometric dating techniques, and the composition of Earth's layers.

Relative Dating

A method to determine the age of rocks and fossils in relation to one another, using principles such as superposition and faunal succession.

Zircon Crystals

Extremely durable crystals that incorporate radioactive uranium, making them valuable for radiometric dating.

Principle of Superposition

In a sequence of sedimentary rock layers, the oldest layers are at the bottom and the younger ones are at the top.

Fossils

Traces or remains of prehistoric life found in sedimentary rocks, which provide evidence of past life.

Paleontology

The study of fossils to understand ancient life and ecosystems.

Index Fossils

Fossils that are widespread but exist for a short geologic period, used to identify and correlate rock layers.

Radiometric Dating

A technique that measures the decay of radioactive isotopes to determine the absolute age of rocks.

Half-life

The time required for half of a radioactive sample to decay into its daughter isotopes.

Unconformity

A gap in the geological record that represents a period of erosion or non-deposition.

Elastic Rebound Theory

A theory explaining how stored energy in rocks is released during an earthquake, causing them to snap back to an original shape.

Seismograph

An instrument that detects and records ground movements caused by seismic waves during an earthquake.

P-waves (Primary waves)

Seismic waves that compress and expand the ground, traveling faster than other waves.

S-waves (Secondary waves)

Seismic waves that move the ground side to side; they cannot travel through liquids.

Hypocenter

The point beneath the Earth's surface where an earthquake rupture starts.

Epicenter

The point on the Earth's surface directly above the hypocenter of an earthquake.

Moho

The boundary between the Earth's crust and the underlying mantle, discovered via seismic refraction.

Geodynamo

The process by which the motion of liquid iron in the outer core generates the Earth's magnetic field.

Conduction

Heat transfer through direct contact, occurring in the crust and inner core, such as a spoon heating in hot tea.

Convection

Heat transfer through the motion of fluids, occurring in the mantle and liquid outer core.

Chemical Differentiation

The process that occurred during Earth's formation whereby heavier elements sank to form the core and lighter elements rose to form the crust.

How old is the Earth?

The Earth is approximately 4.54 billion years old (Ga).

What are Zircon Crystals and their significance?

extremely durable and incorporate radioactive uranium, which is used for radiometric dating.

What is Acasta Gneiss?

one of the oldest known rocks, dated at 4.3 billion years (Ga).

What are meteorites, and how old are they?

remnants from the formation of the solar system, dated at 4.56 billion years (Ga).

What does the Principle of Superposition state?

In a sequence of sedimentary layers, older layers are located beneath younger layers.

Give an example of where the Principle of Superposition is observed.

Volcanic ash deposits in Hawaii and New Zealand illustrate the Principle of Superposition.

What is Original Horizontality?

The principle that sedimentary layers are originally deposited horizontally.

Give an example related to Original Horizontality.

Folding observed in rocks demonstrates deformation of originally horizontal layers.

What does the Principle of Lateral Continuity state?

Layers of sediment initially extend laterally in all directions, resulting in matching layers across gaps.

Provide an example of Lateral Continuity.

The Santa Elena Canyon in Big Bend, TX showcases this principle.

What are Cross-Cutting Relationships in geology?

Intrusions or faults that cut through rocks are considered younger than the rocks they disrupt.

What is an example of Cross-Cutting Relationships?

Quartz veins found in Llano, TX demonstrate cross-cutting relationships.

What does the Principle of Inclusions state?

Fragments within a rock must be older than the rock itself.

Provide an example of Inclusions in geology.

Mantle xenoliths found in lava flows are an example.

What are Unconformities?

represent gaps in the geological record due to erosion or non-deposition.

What are the types of Unconformities?

Conformable layers (continuous deposition), Angular unconformity, Disconformity, and Nonconformity.

What is an Angular Unconformity?

occurs when tilted or folded rocks are overlain by flat-lying rocks.

Give an example of Angular Unconformity.

Siccar Point in Scotland is a classic example.

What is Disconformity?

an erosional surface within parallel sedimentary layers.

What is Nonconformity?

occurs when sedimentary rocks overlie eroded igneous or metamorphic rocks.

What is the Grand Canyon case study known for?

It illustrates multiple geological principles in action, including uplift and incision by the Colorado River.

What are fossils?

traces or remains of prehistoric life found in sedimentary rocks.

What is Paleontology?

the study of fossils.

What is Micropaleontology?

the study of microscopic fossils.

What are examples of index fossils?

species that were widespread but only existed for a short period of time, such as Ammonites.

What does the Principle of Faunal Succession indicate?

Fossils appear in a predictable, chronological order, allowing correlation of rock layers.

What is the significance of index fossils?

They are used to identify and correlate layers across different regions.

What is Radiometric Dating?

measures the decay of unstable isotopes to determine the absolute age of materials.

What is Uranium-Lead Dating?

involves the decay of Uranium-238 to Lead-206; its half-life is about 4.5 billion years.

What is the half-life of Carbon-14?

5,730 years.

What is the Geologic Time Scale based on?

relative dating and radiometric dating.