Earth and Life - Geologic Time Scale & Hazards (Vocabulary)

Vocabulary flashcards covering key terms from Earth science notes on geologic time, dating methods, fossils, rock layers, and geologic hazards.

Geologic time scale

A standard timeline dividing Earth's history into eons, eras, periods, and epochs based on significant events and fossils; used to describe the ages of rocks and life.

Geologic record

The evidence of Earth's history preserved in rocks and fossils.

Eon

The largest division of geologic time; examples include Hadean, Archean, Proterozoic, and Phanerozoic.

Era

A major subdivision of an eon; Phanerozoic is divided into Paleozoic, Mesozoic, and Cenozoic.

Period

A subdivision of an era; examples include Cambrian, Jurassic, and Cretaceous.

Epoch

A subdivision of a period; examples include Holocene and Pleistocene.

Phanerozoic

The eon meaning 'visible life,' characterized by abundant fossil records.

Paleozoic

An era in the Phanerozoic known for early life, a wide variety of fossils, and the appearance of many major animal groups.

Mesozoic

An era in the Phanerozoic known as the 'age of dinosaurs' with the first birds and mammals.

Cenozoic

The current era in the Phanerozoic, often called the 'age of mammals'.

Hadean

The earliest eon of Earth's history, before the formation of continents.

Archean

An eon with early crust formation and some of the first life forms.

Proterozoic

An eon marked by oxygenation and the rise of more complex life before the Paleozoic.

Precambrian

Informal collective term for the time before the Phanerozoic (Hadean, Archean, Proterozoic).

Relative dating

Determining the order of past events without assigning exact numeric ages, often using fossils and rock positions.

Absolute dating

Assigning numeric ages to rocks and events, typically using radioactive decay and material isotopes.

Index fossil

A fossil diagnostic of a specific time interval used to date rocks and correlate strata.

Law of Superposition

In a sequence of undeformed sedimentary rocks, younger layers lie above older layers.

Law of Cross-Cutting Relationships

Features that cut through other rocks or structures are younger than what they cut.

Law of Inclusions

Inclusions are older than the rock that contains them.

Fossil record

The chronological record of life as evidenced by plant and animal fossils in sedimentary rock.

Sedimentary rock

Rock formed by deposition and lithification of sediment, often containing fossils.

Geologic hazard

An extreme natural event in the Earth's crust that threatens life and property.

Ground shaking

Movement of the ground during an earthquake; a primary hazard that can trigger other hazards.