Historical Geology Test Study Guide 21-22

These flashcards cover essential concepts in historical geology, including relative and absolute dating, types of fossils, geologic time scales, and significant geological events.

What is relative dating in geology?

the placing of rock layers in chronological order without assigning specific ages.

What does Steno's Principle of Horizontality state?

It states that sediment is deposited in flat horizontal layers; any disturbance must have occurred after their formation.

What is the Law of Superposition?

In an undisturbed sequence of sedimentary rocks, the oldest layers are at the bottom and the youngest are at the top.

Explain Cross-Cutting Relationships.

Faults, folds, inclusions, and igneous intrusions are younger than the rocks they cut through.

What is an unconformity?

a gap in the rock record caused by weathering and erosion that removes layers of rocks.

Define absolute dating.

provides a reliable age for a rock or fossil by analyzing its chemical components.

What is a half-life in geology?

The time it takes for half of the unstable parent atom to decay into a stable daughter atom.

What is a fossil?

a preserved remain or trace of an organism.

What are petrified fossils?

organic material is replaced by minerals, resulting in a rock-like structure.

How are molds and casts formed?

Molds are formed when a shell or structure is buried and dissolves; casts form when the mold is filled in with minerals.

What are trace fossils?

provide indirect evidence of ancient life, including footprints and burrows.

What defines index fossils?

organisms that existed for a short period but were widespread, making them useful for correlation.

What was significant about the Precambrian Era?

It lasted 4 billion years, has an incomplete rock record, and showed the development of the first life forms.

What event is marked by the Cambrian Explosion?

a time when life diversified significantly, leading to many fossils.

What caused the Permian mass extinction?

volcanic eruptions leading to major climate changes.

What characterized the Mesozoic Era?

Age of Reptiles and Dinosaurs, featuring significant evolutionary developments.

What key event occurred at the end of the Cretaceous period?

mass extinction event possibly caused by an asteroid impact.

What is the Cenozoic Era known for?

Age of Mammals, during which modern plants and animals evolved.