Chapter 12: Earth's Evolution through Geologic Time

Supernova

An exploding star that increases in brightness many thousands of times.

Solar Nebula

The cloud of interstellar gas and/or dust from which the bodies of our solar system formed.

Planetesimal

A solid celestial body that accumulated during the first stages of planetary formation. These are aggregated into increasingly larger bodies, ultimately forming the planets.

Protoplanet

A developing planetary body that grows by the accumulation of planetesimals.

Hadean

A term found on some versions of the geologic time scale. It refers to the earliest interval (eon) of Earth history and ended 4 billion years ago.

Outgassing

The escape of gases that had been dissolved in magma.

Banded Iron Formations

A finely layered iron and silica rich (chert) layer deposited mainly during the Precambrian.

Great Oxygenation Event

A time about 2.5 billion years ago, when a significant amount of oxygen appeared in the atmosphere.

Craton

The part of the continental crust that has attained stability; that is, it has not been affected by significant tectonic activity during the Phanerozoic eon. It consists of the shield and stable platform.

Shield

A large, relatively flat expanse of ancient metamorphic rock within the stable continental interior.

Supercontinent

A large landmass that contains all, or nearly all, of the existing continents.

Supercontinent Cycle

The idea that the rifting and dispersal of one supercontinent is followed by a long period during which the fragments gradually reassemble into a new supercontinent.

Prokaryote

Cells or organisms such as bacteria whose genetic material is not enclosed in a nucleus.

Stromatolite

Structures that are deposited by algae and consist of layered mounds of calcium carbonate.

Eukaryote

An organism whose genetic material is enclosed in a nucleus; .

Cambrian Explosion

The huge expansion in biodiversity that occurred at the beginning of the Paleozoic era.

Mass Extinction

An event in which a large percentage of species become extinct.

Gymnosperm

A group of seed-bearing plants that includes conifers and Ginkgo. The term means "naked seed," a reference to the unenclosed condition of the seeds.

Angiosperm

A flowering plant in which fruits contain the seeds.