GEOL 105 Planet Earth

Planetary accretion

The process by which stars planets and moons form through the accumulation of gas dust and debris from the original nebula.

Planetary differentiation

The process of separating materials inside a planet based on density and chemistry. Dense materials sink toward the center while less-dense materials rise toward the surface and the planet develops compositionally distinct layers.

Earth's layers

Earth has a solid metallic inner core a liquid metallic outer core a silicate-rich mantle and a crust that concentrates lighter elements.

Moon formation

The Moon formed when Earth collided with Theia a Mars-sized planet. Theia was absorbed by Earth and debris from the collision compacted to form the Moon.

Theia

A Mars-sized planet that collided with early Earth and contributed material that formed the Moon.

Moon distance

The Moon's distance from Earth evolved from about 24

Length of Earth's day

Earth's days lengthened from about 5 hours early in its history to 24 hours today as the Moon moved farther away.

Earth's secondary atmosphere

Earth's oceans and atmosphere developed after planetary differentiation as the planet cooled and gases and water were released from the crust and mantle.

Degassing

The release of gases and water from Earth's crust and mantle as the planet cooled.

Comets

Objects made largely of ice and rock from the outer solar system that contributed additional water to early Earth.

Volcanic outgassing

The release of volcanic gases including water vapor from Earth's interior as Earth cooled.

Current volcanic gases

Modern volcanoes emit about 50-60% H2O 24% CO2 13% SO2 and 3% other gases.

Early atmosphere

Earth's early atmosphere contained no oxygen.

Global ocean

Early Earth likely had a global ocean because there were few topographic features to prevent water from covering the surface.

Jack Hills ocean evidence

Ancient sediments and zircons from Jack Hills Australia indicate that an ocean existed as far back as about 4.4 billion years ago.

Surface tension

The property of water that allows droplets to form and makes rainfall possible.

Water cycle

The rapid movement of water through Earth's atmosphere and surface enabled partly by water's ability to form droplets.

Water vapor

An important greenhouse gas because Earth radiates energy mainly in infrared wavelengths.

Young faint Sun paradox

The early Sun was about 30% less luminous than today so Earth should have been frozen

Methane

CH4. A greenhouse gas that helped maintain a warmer early Earth and may also have supplied organic material that contributed to the building blocks of life.

Geodynamo

The process that generates Earth's magnetic field through the movement of conductive material in the liquid outer core. Earth's rotation and internal convection help create the geomagnetic field.

Geomagnetic field

Earth's magnetic field generated by the motion of conductive material in the outer core.

Magnetosphere

The region dominated by Earth's magnetic field that shields the planet from most charged particles from the solar wind and cosmic rays.

Solar wind

Charged particles flowing from the Sun that are largely deflected by Earth's magnetic field.

Ozone layer

A layer that protects Earth from harmful ultraviolet radiation. Earth's magnetic field helps protect conditions that allow the ozone layer to persist.

Age of Earth

About 4.56 billion years or 4.56 Gyr.

Meteorites

Leftover pieces from solar system formation that provide evidence for an Earth and solar system age of about 4.56 billion years.

Planetary accretion age

Planetary accretion began about 4.56 ± 0.01 billion years ago according to meteorite evidence.

Oldest Moon rocks

About 4.47 billion years old based on rocks collected by Apollo missions.

Oldest zircons

About 4.4 billion years old and found in Australia. They indicate that Earth's crust and liquid water existed very early in Earth's history.

Acasta Gneiss

The oldest known intact crustal fragment on Earth located in the Northwest Territories of Canada. It was metamorphosed about 3.5-4 billion years ago and originated as a granitoid that formed around 4 billion years ago.

Jack Hills zircons

Zircons from Western Australia containing Earth's oldest known minerals at about 4.4 billion years old. Their presence in younger sedimentary rock shows that an earlier water and rock cycle existed.

Big six elements

Oxygen silicon aluminum magnesium calcium and iron. Together they make up about 98% of Earth's mass.

Chemical bonds

Connections between atoms formed when atoms share or transfer electrons or when metals form a shared sea of electrons.

Magic numbers

Electron arrangements involving 2 10 or 18 electrons that represent especially stable configurations.

Covalent bond

A chemical bond in which atoms share electrons. Examples include H2O N2 NH3 CH4 CO and CO2.

Ionic bond

A bond formed through the transfer of electrons between atoms which creates oppositely charged ions that attract each other.

Metallic bond

A bond in metals where positively charged atomic nuclei are surrounded by a sea of delocalized electrons. The mobile electrons make metals excellent electrical conductors.

Ion

An atom with an excess positive or negative charge caused by gaining or losing electrons.

Neutral atom

An atom in which the positive charge of protons balances the negative charge of electrons.

Sodium ion

Sodium becomes a positive ion when it loses an electron.

Chlorine ion

Chlorine becomes a negative ion when it gains an electron.

Delocalized electrons

Electrons in metals that are free to move throughout the material rather than being tied to one specific atom.

Iron ions

Iron can form Fe2+ and Fe3+ ions.

Evidence for Earth's composition

Scientists use Earth's magnetic field gravitational effects and spin seismic waves volcanic rocks such as kimberlite and meteorites to study Earth's internal composition and structure.

Magnetic field evidence

A magnetic field provides evidence for a metallic core because moving conductive material generates the field.

Seismic waves

Earthquake waves used to identify boundaries between layers inside Earth.

Kimberlite

A volcanic rock that can transport materials from deep within Earth toward the surface.

Mineral

A naturally occurring inorganic solid material with a well-defined chemical composition.

Crystal structure

The way atoms in a mineral are packed and arranged.

Mineral composition

The major chemical elements present in a mineral and their proportions.

Pyrite

FeS2. A mineral commonly found in quartz veins sedimentary and metamorphic rocks coal beds and as a replacement mineral in fossils.

Oxygen

Oxygen is Earth's master electron acceptor and about 99.9999% of Earth's oxygen is locked into rocks and minerals. Its strong tendency to accept electrons makes it highly reactive and corrosive.

Silicon

Silicon is a major electron donor and accounts for nearly 1 in every 4 atoms in Earth's crust and mantle. It commonly gives away 4 electrons and forms strong bonds with oxygen.

Quartz

SiO2. A common mineral built from strong silicon-oxygen bonds and an example of a three-dimensional framework silicate.

Oxides

Minerals in which the oxide ion O2- is bonded to one or more metals. Examples include periclase hematite and magnetite groups.

Magnetite

Fe3O4. An example of an oxide mineral.

Silicate minerals

The most common rock-forming minerals on Earth. They are based on silicon and oxygen and include quartz feldspar olivine garnet mica and asbestos.

Silicate tetrahedron

The fundamental building block of silicate minerals consisting of one central silicon atom bonded to four surrounding oxygen atoms. It has a pyramid-like shape and an overall -4 charge.

Polymerization

The process in which silicate tetrahedra link by sharing oxygen atoms to form larger structures such as chains sheets and three-dimensional frameworks.

Isolated tetrahedra

Silicate structures in which tetrahedra remain separate. Example: olivine.

Single chain silicates

Silicate structures in which tetrahedra form single chains. Example: pyroxene.

Double chain silicates

Silicate structures in which tetrahedra form double chains. Example: amphiboles.

Sheet silicates

Silicate structures in which tetrahedra form sheets. Examples include clays mica talc chlorite and serpentinite.

Framework silicates

Silicate structures in which tetrahedra form three-dimensional frameworks. Examples include quartz and feldspar.

Olivine

An example of a silicate mineral with isolated tetrahedra.

Pyroxene

An example of a silicate mineral with a single-chain structure.

Amphibole

An example of a silicate mineral with a double-chain structure.

Mica

An example of a sheet silicate.

Feldspar

An example of a framework silicate and one of the most common rock-forming minerals.

Carbonates

Minerals containing the carbonate ion. Calcite is an important example.

Calcite

A carbonate mineral that can precipitate from calcium-rich water. Biological calcite from shells and bones can contribute to limestone.

Aragonite

A mineral with the same chemical composition as calcite but a different crystal structure.

Polymorphs

Minerals that have the same chemical composition but different crystal structures. Calcite and aragonite are polymorphs of CaCO3.

Silicate weathering

The breakdown of silicate rocks by weak carbonic acid formed when rainwater absorbs atmospheric CO2. The process releases calcium and bicarbonate and helps transfer atmospheric CO2 into limestone on the ocean floor.

Earth's thermostat

Silicate weathering acts as an Earth thermostat because it removes atmospheric CO2 and helps regulate Earth's greenhouse effect and climate.

Carbonic acid

A weak acid formed when rainwater absorbs CO2 from the atmosphere. It reacts with silicate rocks during weathering.

Limestone

A rock that can form when calcium carbonate from marine organisms accumulates on the seafloor. It represents a long-term storage location for atmospheric CO2.

Silicate weathering reaction

CO2 + CaSiO3 → CaCO3 + SiO2.

Sulfates

Mineral salts containing the sulfate ion SO4^2-.

Gypsum

A sulfate mineral composed of calcium sulfate dihydrate with the formula CaSO4·2H2O. It is common in evaporite beds and occurs in the Mojave Desert due to ancient lake desiccation.

Evaporite beds

Sedimentary deposits formed when water evaporates and leaves minerals such as gypsum behind.

Phosphates

Minerals containing the phosphate ion PO4^3-.

Apatite

The most common phosphate mineral and an important source of phosphorus for plants. It is a calcium phosphate found in animal bones and teeth and can be used in U-Pb radiometric dating.

U-Pb dating

A radiometric dating method that uses uranium and lead isotopic compositions to estimate the age of minerals such as apatite.

Closure temperature

The temperature below which a mineral's isotopic system becomes effectively closed to diffusion. Apatite has a U-Pb closure temperature of about 500°C.

Mineral evolution

The development of new mineral species through combinations of chemical physical and biological processes over Earth's history.

Ur minerals

About 12 of the earliest mineral types including diamond and graphite that formed in the solar nebula from a small number of essential elements.

Chondrite minerals

About 60 mineral species present in early chondritic meteorites as Earth formed and differentiated.

Prebiotic mineralogy

The development of about 1

Great Oxidation Event

The major rise of atmospheric oxygen about 2.4 billion years ago caused by photosynthetic life such as algae and phytoplankton. Oxygen oxidized existing minerals and contributed to more than 2

Late organic evolution

Beginning about 450 million years ago the development of multicellular organisms and biomineralization in exoskeletons shells and bones contributed hundreds of additional mineral species.

Fractional crystallization

A geological process that contributed to the formation of many new mineral species on early Earth.

Biomineralization

The biological production of mineral materials in structures such as shells bones and exoskeletons.