Earth Science and Geologic Time Scale Practice Flashcards

This set of vocabulary flashcards covers the layers and chemical composition of the Earth, geological dating principles, and the hierarchy of the Geologic Time Scale from the Hadean Eon to the Holocene Epoch.

Earth Science

The study of the Earth's structure, properties, and processes, also referred to as geoscience.

Astronomy

The study of how Earth relates in space and time.

Meteorology

The study of how atmosphere conditions relate to weather and climate.

Oceanography

The study of how marine ecosystems interact in the oceans.

Geology

The study of how Earth's landforms and rock change over time.

Inner Core

The solid, extremely dense, and hot innermost layer of the Earth made up mostly of iron and nickel.

Outer Core

The liquid layer of iron and nickel whose motion generates electric currents and the Earth’s magnetic field.

Mantle

A layer made mainly of iron, magnesium, and silicon that behaves like a viscous liquid despite being mostly solid.

Crust

The thinnest, solid outer layer of Earth composed mainly of relatively light elements like oxygen, silicon, and aluminum.

Lithosphere

The rocky outer part of the Earth composed of the crust and the uppermost part of the mantle, subdivided into tectonic plates.

Asthenosphere

A layer of highly viscous partially melted rock in the upper mantle upon which tectonic plates ride and slide.

Mesosphere

The lower mantle, which is more rigid and less ductile than the upper mantle due to great pressure.

Oceanic Crust

A dark, dense, and low-silica crust mainly composed of basalt, measuring approximately $3$ to $5$ miles ($8\,km$) in thickness.

Continental Crust

A thick crust composed mostly of granite and rich in silicates, measuring up to $25$ miles ($32\,km$) under continents.

Basalt

An extrusive, mafic igneous rock common on most silicate terrestrial planetary bodies, forming in days to months.

Granite

An intrusive, felsic igneous rock usually associated with continental crust that takes millions of years to form.

Mohorovicic Discontinuity (Moho)

The boundary marking the transition between the Earth's crust and the upper mantle.

Lehmann Discontinuity

The boundary located between the outer core and the inner core.

Relative Dating

A method based on stratigraphy used to determine the order of events without providing an exact age in years.

Absolute Dating

Also known as actual dating, this provides the specific age of a rock, fossil, or event in years.

Law of Superposition

The principle that sediments build up over time in layers, where the oldest rocks are at the bottom.

Principle of Original Horizontality

The principle stating that sediments usually settle in flat, level layers, and tilted layers suggest disturbance.

Principle of Lateral Continuity

The idea that sedimentary layers initially extend in all directions until they thin out or terminate at edges.

Principle of Cross-Cutting Relationships

The principle that any feature cutting across rock layers is younger than the layers it cuts.

Radioactive Decay

The process where radioactive elements gradually transform into different elements until they stabilize.

Half-life

The unit of time it takes for half of a radioactive element to decay.

Geologic Time Scale (GTS)

The hierarchy of time units including eons, eras, periods, and epochs used to divide Earth's lifetime based on major events.

Hadean Eon

The eon from $4.54 - 4.0$ billion years ago characterized by a molten surface and heavy meteorite bombardment.

Archaean Eon

The eon from $4.0 - 2.5$ billion years ago where the first stable crust and oceans formed, and earliest life appeared.

Proterozoic Eon

The eon from $2.5\,billion - 541\,million$ years ago where oxygen built up in the atmosphere and complex cells appeared.

Phanerozoic Eon

The eon beginning $541\,million$ years ago characterized by abundant fossils and flourishing plant and animal groups.

Cambrian Explosion

A turning point in the Cambrian period marked by a sudden and rapid diversification of major animal groups.

Paleozoic Era

Known as 'ancient life', spanning from $541 - 252\,million$ years ago, featuring the diversification of marine life and first land plants.

Mesozoic Era

Known as 'middle life', spanning from $252 - 66\,million$ years ago, characterized as the age of dinosaurs.

Cenozoic Era

Known as 'recent life', spanning from $66\,million$ years ago to the present, where mammals dominate and humans emerged.

Pleistocene Epoch

The epoch from $2.6\,million - 11,700$ years ago characterized by ice ages and the worldwide spread of early humans.

Holocene Epoch

The current epoch starting $11,700$ years ago, marked by a warming climate and the development of human civilization.