Earth Science: Key Concepts on Earth's Spheres, Plate Tectonics, and Earthquakes

What is Earth Science?

Earth Science studies interactions among the atmosphere, hydrosphere, biosphere, geosphere, and exosphere.

Four main Earth spheres

Atmosphere, hydrosphere, biosphere, geosphere.

Exosphere

The sun and space interacting with Earth.

Goals of Earth scientists

Identify processes, understand them, monitor change, predict trends, inform society.

Direct measurements

Data collected directly in the field (ex: soil sample).

Indirect information

Data used to infer something else (ex: seismic waves).

Modeling

Computer or physical simulations of Earth processes.

Hypothesis requirements

Testable, predictable, empirical, natural explanation.

Inductive reasoning

Specific observations → general conclusion.

Deductive reasoning

General principle → specific prediction.

Hazard prevention

Scientists warn of hazards; prevention vs. adjustment.

Renewable resources

Replenish quickly (soil, trees, crops).

Nonrenewable resources

Form over millions of years (coal, oil, minerals).

Sustainable society

Uses resources without harming future generations.

Environmental protection

Prevents pollution, deforestation, ecosystem damage.

Global threats studied

Climate change, asteroid impacts.

Continental drift

Wegener's idea that continents formed Pangaea and drifted apart.

Evidence for continental drift

Fossils, mountains, climate, rock matches, continental fit.

Why Wegener was rejected

No mechanism for movement.

Pangaea

Supercontinent ~250 million years ago.

Plate tectonics

Lithosphere broken into moving plates.

Earth's layers

Core, mantle, crust.

Seafloor topography

Shelves, abyssal plains, ridges, trenches.

Seafloor spreading

New crust forms at ridges; destroyed at trenches.

Ways mantle melts

Increase temperature; decrease pressure; add water.

Hot spot volcanism

Volcanic chains from mantle plumes (ex: Hawaii).

Divergent boundary

Plates move apart.

Convergent boundary

Plates collide (subduction or collision).

Transform boundary

Plates slide past each other.

Earthquake fault

Fracture where rocks move.

Focus

Point underground where quake begins.

Epicenter

Point on surface above focus.

Normal fault

Hanging wall moves down (tension).

Reverse fault

Hanging wall moves up (compression).

Strike-slip fault

Horizontal motion.

P-waves

Fastest; compressional; travel through any material.

S-waves

Slower; up-down motion; travel only through solids.

Surface waves

Slowest but most destructive.

Richter scale

Measures wave amplitude; outdated.

Moment magnitude

Measures energy released (modern).

Mercalli scale

Measures observed damage.

Liquefaction

Saturated ground behaves like a liquid.

Tsunami

Large waves from displacement (quakes, landslides, volcanoes).

Magma vs lava

Magma underground; lava at surface.

Viscosity

Resistance to flow.

Silica content effect

More silica = more viscous = more explosive.

Basaltic magma

Low silica, gentle eruptions.

Rhyolitic magma

High silica, explosive eruptions.

Pyroclastic flow

Fast, deadly gas + ash cloud.

Lahar

Mudflow of volcanic debris and water.

Shield volcano

Wide, gentle slope (Mauna Loa).

Stratovolcano

Steep, explosive (Mount St. Helens).

Cinder cone

Small cone of tephra.

Caldera

Collapse into empty magma chamber.

Five mineral criteria

Natural, inorganic, solid, definite composition, crystalline structure.

Most abundant crust elements

Oxygen and silicon.

Ionic bonds

Transfer electrons; weak.

Covalent bonds

Share electrons; strong.

Silicate minerals

Silicon + oxygen (quartz, feldspar).

Crystal form

External shape based on atomic structure.

Hardness

Resistance to scratching (Mohs scale).

Cleavage

Breaks along planes.

Fracture

Irregular break.

Igneous rocks

Form from cooling magma or lava.

Extrusive igneous

Cool quickly; fine-grained.

Intrusive igneous

Cool slowly; coarse-grained.

Sedimentary rocks

Form from weathering, deposition, lithification.

Clastic sedimentary

Made of fragments (sandstone, shale).

Chemical sedimentary

From precipitation (rock salt).

Biochemical sedimentary

From organisms (limestone).

Metamorphic rocks

Form from heat and pressure.

Foliation

Alignment of minerals from pressure.

Rock cycle

Any rock can become another.

Earth's age

4.6 billion years.

Relative dating

Places events in order.

Absolute dating

Gives numerical ages.

Superposition

Oldest at bottom, youngest at top.

Original horizontality

Layers deposited flat.

Cross-cutting relationships

Feature that cuts another is younger.

Inclusions

Fragments inside another rock are older.

Half-life

Time for half of parent isotope to decay.

Index fossils

Widespread, short-lived fossils used for correlation.

Major eons

Archaean, Proterozoic, Phanerozoic.

Stream

Flowing water in a channel.

Drainage basin

Area drained by a stream system.

Meander

Bend in a stream.

Floodplain

Flat area formed by flooding.

Discharge

Width × depth × velocity.

Aquifer

Permeable rock storing water.

Aquitard

Low-permeability layer.

Porosity

% of pore space.

Permeability

Ability for water to flow through material.

Cone of depression

Lowered water table around a pumped well.

Saltwater intrusion

Seawater pulled into aquifers.

Wetlands

Saturated land forming natural filters.

Ocean salinity

Average 3.4%.

Thermocline

Rapid temperature drop with depth.

Gyre

Circular ocean current.

Thermohaline circulation

Global conveyor belt.

El Niño

Warm Pacific; rain in Americas.