A Trip Through Earth's History

A set of vocabulary flashcards covering key terms and concepts related to Earth's history and the study of fossils.

Fossils

Preserved remains or traces of living things.

Paleontologist

A scientist who studies, collects, and classifies fossils.

Mold

A hollow area in the sediment showing the shape of an organism.

Cast

A solid copy of the shape of an organism.

Petrified Fossil

Fossils in which minerals replace all or part of an organism.

Carbon Film

An extremely thin coating on rock.

Trace Fossil

Fossils that provide evidence of the activities of ancient organisms.

Fossil Record

Information gathered by paleontologists that provides evidence of the history of life on Earth.

Evolution

Gradual change in living things over long periods of time.

Scientific Theory

A well-tested concept that explains a wide range of observations.

Extinct

When an organism no longer exists and never will again.

Relative Age

The age of a rock compared with the ages of other rocks.

Absolute Age

The number of years since the rock formed.

Law of Superposition

In horizontal sedimentary rock layers, the oldest layer is at the bottom.

Extrusions

Lava that hardens on the surface (igneous rocks).

Intrusions

Magma that cools and hardens into a mass of igneous rocks beneath the surface.

Fault

A break in Earth’s crust that is always younger than the rock it cuts through.

Unconformity

A gap in the geological record where rock layers have been lost due to erosion.

Index Fossil

A fossil that is widely distributed and represents an organism that existed briefly.

Radioactive Dating

A method used to determine the absolute ages of rocks.

Element

All the atoms of a particular type of matter are the same.

Radioactive Decay

The process by which one unstable element breaks down into another stable element.

Half-life

The time required for half of the unstable element to decay.

Geological Time Scale

A system that divides Earth’s history into units of time.

Eon

The longest subdivision of geological time based on the abundance of fossils.

Era

A subdivision marked by significant changes in the types of fossils present.

Period

A unit based on types of existing life globally at a particular time.

Epoch

Subdivisions of periods characterized by differences in life forms.

Cenozoic Era

The youngest era divided into two periods.

Mesozoic Era

The middle era divided into three periods, often called the Age of Reptiles.

Paleozoic Era

The oldest era divided into six periods, often called the Age of Invertebrates.

Precambrian Time

Covers about 88% of Earth’s history and lasted from 4.6 billion to 544 million years ago.

Cyanobacteria

The earliest life forms to appear, adding oxygen to the atmosphere.

Mass Extinction

A significant, widespread, and rapid decrease in the biodiversity of life on Earth.

Pangaea

The supercontinent that existed during the late Paleozoic and early Mesozoic eras.

Angiosperms

Flowering plants that became dominant during the Cenozoic era.

Holocene Epoch

The current epoch of the Quaternary period.

Ordovician

A period in the Paleozoic era known for significant marine life.

Jurassic

A period marked by the dominance of dinosaurs.

Carboniferous

A period in the Paleozoic era known as the Age of Amphibians.

Triassic

The first period of the Mesozoic era.

Himalayas

Mountain ranges formed by the collision of India with Asia.

Fossil Formation

Occurs when living things die and are buried by sediments.

Extinction Event

A dramatic and sudden reduction in biodiversity.

Sedimentary Rock

Rock formed by the accumulation and compression of sediments.