01 Geology Basics

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The Earth's interior is characterized

by a gradual increase in

temperature, pressure and density

with depth.

At only 100 km depth, the temp is

~1300C.

At the Earth's center, the

temperature is >6700C.

The pressure in the crust increases

~280 bars for every kilometer depth.

Earth's Internal Structure


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Earth's Internal StructureThe Earth consists of 3 major

regions marked bydifferences in chemicalcomposition.

Crust: rigid outermost layer of

the Earth. Consists of two

types:

1. oceanic- 3-15 km thickand is composed of

basalt (igneous). Young

(3.8 billion years old).


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The Interior of the Earth (overall density = 5.5 g/cm3

) Earths interior is determined by analyzing travel times

of two types of waves generated by earthquakes.

Earths interior is made up of three layers: Crustis the thin (


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Layering by Strength Most of the Earth is not molten and most of the

lava from volcanoes rises upward from anarrow region of the mantle which is partially

molten. The shape of a planet is determined by the

strength and fluidity of the inside as well as thestrength of gravity Large worlds (> 500 km diameter) are round

Small worlds are irregular in shape

The crust and the top part of the mantle isrelatively cool region of rock called thelithosphere that floats on the rest of the

mantle. 7


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Geological Activitydescribes how much

ongoing change occurs on the surface of

a solar system body Interior heat is the primary driver for

geological activity

But how do interior heat up and cool off?

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How planets heat up Heat of accretion

Energy brought from afar from colliding planetesimalspotential energyconverted into kinetic energy

Heat of differentiation

As the planet redistributes its mass and denser material sinks towardsthe core gravitational potential energy is converted to thermal energy viafriction

Heat from radioactive decay Decay from radioactive materials heats up the interior as some of the

nuclear decay energy ( E = mc2) gets transferred to thermal energy

Note: the first of these two tend to happen early in a planets historywhile the last (radioactive decay) happens throughout the history ofthe planet, but is strongest at the beginning of the formation of theplanet. Radioactive decay likely contributes several times moreenergy over the life of the planet than does accretion anddifferentiation.

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How Interiors Cool Off: Conduction

Transfers occurs between atoms Examples: metal rod in fire, Earths core and lithosphere

Convection Warmer (less dense) air rises and carries energy into cooler (denser)

regions Requires large temperature gradient Examples: Lava lamp, Earth atmosphere and mantle, Suns outer layers

Radiation Photons directly transfer energy Less efficient in high density situations Photons take ~ 200,000 years to get of Sun. Examples: Heat lamp, Earths surface, Suns interior

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How the Earth moves energy from the core tothe surface:

Convection is the most important process inthe Earths deep interior

The ongoing process of transferring heat upwardcreates convection cells

Ongoing mantle convection goes at the rate of 1cm/year: It would take about 100 million years to

move the mantle from the base to the topAt the lithosphere, conduction is probably the

most important process

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Earths Magnetic FieldA magnetic fieldis a region of space

where magnetic forces can bedetected. The region around a planet is

called a magnetosphere Earths magnetic poles are not locatedat its poles of rotation. The location ofthe magnetic poles changes with time.

Dynamo effectis the model that

explains the Earths and other planetsmagnetic fields as due to currentswithin a liquid iron core and a rapidlyspinning planet.

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TheVan Allen beltsare doughnut-shaped regions composed of chargedparticles (protons & electrons) emitted

by the Sun & captured by the magneticfield of the Earth.

Aurorasresult from disturbances in

the Earths magnetic field that causesome of the particles to follow themagnetic field lines down to theatmosphere, where their collisions with

atoms of the air cause it to glow. 14


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There are 4 processes which shape thevirtually all features on Earth

1. Impact Cratering Bowl shaped from asteroids or meteors

2. Volcanism Eruption of lava from planets interior

3. Tectonics Disruption of planets surface by internal

forces

4. Erosion Wearing down or building of geologicalfeatures by wind, water, ice etc

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As a general rule the craters made by meteorsare 10 times bigger than the impactor and 10-20% as deep as the crater is wide.

Most impacts happened very early in the historyof the solar system

The most prominent impact crater on Earth is

Meteor Crater near Winslow, Arizona (only50,000 years ago).

Many of the craters on the Earth have beenwiped out by erosion processes

Not true for Moon and Mercury 16


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Volcanism occurs when underground moltenrock finds it way through the lithosphere. This isdue for 3 reasons:

Molten rock is generally less dense than solid rock Most of the Earths interior is not molten and it

requires a chamber of molten rock to be squeezedup the surface

Molten rock often has gas inside of it, leading to

dramatic eruption and to outgassing The most common gasses released are water

vapor, carbon dioxide, nitrogen, and sulfurgasses (H2S or SO2)

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A relatively recent theory that the Earth's

crust is composed of rigid plates that

move relative to one another.

Plate movements are on the order of a

few centimeters/year - about the same

rate as your fingernails grow!

Plate Tectonics

There are 3 types of plate

boundaries:1. divergent

2. convergent

3. transform


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Plate TectonicsConvergent boundaries- plates move together forming a subduction zone

and mountain chains.

Divergent boundaries- plates move apart forming the mid-ocean ridge and

seafloor spreading.Transform boundaries- plates grind past one another. These boundaries

subdivide the mid-ocean ridge and also form the San Andreas fault system.


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A simplifed model of tectonic plates

and the location and nature of

earthquakes.


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Plate Boundaries: where the real action occurs.

The plates are all moving relative to each other. At the boundary between two plates,

there must be some motion of one relative to the other. You get three possibilities:

Spreading center: Divergent boundary

At the top of a rising convection limb. Heat is being brought up. Volcanism. Usually

under-ocean. Often associated with a rift valley.

Collision zone: Convergent boundaryCold lithosphere bends downward and begins sinking into the mantle (subduction).

Mountains are squeezed up here by the collision. Most earthquakes occur here.

Parallel plate motion: Transform / Transcurrent / Strike Slip faulting

The San Andreas Fault is the most famous transform fault system.


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Plate Margins


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The surface of the Earth is changed byerosion, the processes that break down ortransport rock through the action of ice, liquid,or gas Valleys shaped by glaciers

Canyons carved by rivers

Shifting of sand dunes by the air

Erosion can pile up sediments into layers calledsedimentaryrocks (Ex. Grand Canyon)

The Earth has the most erosion of anyterrestrial planet

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The number of craters in a given regioncan tell one the age of the planet/moon

since the last major change on surface

Does not necessarily indicate formation age

Erosion from wind, water, and lava will

wipe out craters in a given region

This led to determining the development ofdifferent parts of the planet/moon

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Age of surfaces


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Absolute (Radiometric) Dating:Using radioactive decay ofelements to determine the absolute age of rocks. This is done using igneous andmetamorphic rocks.

Geologic Time

G l i Ti


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The concept of geologic time is new

(staggering) to many nongeologists.

The current estimate is that the Earthis ~4,600,000,000 (4.6 billion) years

old.

As humans we have a hard time

understanding the amount of timerequired for geologic events.

We have a good idea of how long a

century is. One thousand centuries is

only 100,000 years. That huge amount

of time is only 0.002% of the age of the

Earth!

An appreciation for the magnitude of

geologic time is important because

many processes are very gradual.

Geologic Time


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Geologic time is divided into different

types of units.

Note that each Eon, Era or Period

represents a different amount of time. For

example, the Cambrian periodencompasses ~65 million years whereas

the Silurian period is only ~30 million years

old.

The change in periods is related to the

changing character of life on Earth and

other changes in environment.

The beginning of the Phanerozoic

represents the explosion of life.

The time before the Phanerozoic is

commonly referred to as the PreCambrian

and represents over 4 billion years of time.

The Phanerozoic eon (abundant life)

represents only the last 13% of Earth time.

01 Geology Basics

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