Geology

scientific method

a process scientists use to study and understand the world

what are the steps of scientific method?

observe

question

research

hypothesize

experiment

test

draw conclusions

report

Hypothesis

a proposed explanation for an observation that can be tested

theory

An accepted scientific idea that explains a process using the best available information

Catastrophism

the idea that large, damaging events are the cause of most geologic features

Uniformitarianism

The present is the key to the past, meaning the physical laws and properties that existed and operated in the past still exist and operate today

Principle of parsimony/Occam’s razor

The principle that, of two explanations that account for all the facts, the simpler one is more likely to be correct.

Big Bang

the theory that the universe started with an expansive explosion, shortly after, elements were created and galaxies started to form.

Solar nebular hypothesis

the idea that a nebula can colapse and form a star with planets

Giant impact hypothesis

idea that a large body struck the Earth, sprayed material into space, and that material eventually collected to form the moon.

Planetary accretion

The process in which solids accumulate to form larger and larger objects, eventually forming planets.

Chemical differentiation

The process of separating out different constituents of a planetary body as a consequence of their physical or chemical behavior, where the body develops into compositionally distinct layers.

Inner core

The innermost physical layer of the Earth, which is solid.

outer core

The outer physical layer of the core, which is liquid. Movement within the outer core is believed to be responsible for Earth's magnetic field.

mantle

The layer of hot, solid material between Earth's crust and core.

Oceanic crust

The thin, outer layer of the Earth which makes up the rocky bottom of the ocean basins. It is made of rocks similar to basalt, and as it cools, even become more dense than the upper mantle below.

Continental crust

The layers of igneous, sedimentary, and metamorphic rocks that form the continents. Continental crust is much thicker than oceanic crust and much less dense. Its average composition is similar to granite.

Hydrosphere

The water part of the Earth, as a solid, liquid, or gas.

Atmosphere

The gases that are part of the Earth, which are mainly nitrogen and oxygen

Biosphere

The living things that inhabit the Earth

Geosphere

The rocky parts of the Earth, including the crust, mantle, and core.

Convection

The property of unevenly-heated (heated from one direction) fluids (like water, air, ductile solids)

in which warmer, less dense parts within the fluid rise while cooler, denser parts sink.

This typically creates convection cells: round loops of rising and sinking material.

Uniformitarianism

The present is the key to the past.” Geological processes happening now (like erosion, volcanoes, earthquakes) worked the same way in the past.

Geologists use it to understand Earth’s history and predict how landforms formed over time.

steps of scientific method

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catastrophism

earth shaped by sudden,short,violent events (like huge floods or asteriod impacts)

how old is the earth?

4.6 billion years old

the four earth spheres

lithosphere

hydrosphere

atmosphere

biosphere

lithosphere

solid rock/land (crust and upper mantle)

Hydrosphere

ALL WATER (hydro) (oceans,rivers,lakes)

atmosphere

gases surrounding earth (air)

biosphere

all living things (plants and animals)

what are the two sources of earths energy?

Internal heat - drives volcanoes, earthquakes, plate tectonics

solar energy - drives weather, climate, and ocean currents

What is the Solar Nebular hypothesis? What evidence supports this hypothesis?

The Sun and planets formed from a spinning cloud of gas and dust (nebula) about 4.6 billion years ago.

what evidence supports the Solar Nebular hypothesis?

• Most planets orbit in the same plane and direction
  
  

• Composition of planets matches what we’d expect from a cooling nebula
  
  

• Observations of new star systems forming today

How and when did the Moon form?

Formed about 4.5 billion years ago

From a giant impact: a Mars-sized object hit Earth, and debris from the collision coalesced into the Moon.

By what process did Earth separate into its different compositional zones?

Differentiation:

Earth heated up, melted internally, and denser materials sank to form the core, while lighter materials formed the crust and mantle.

Explain the features of Earth that make it unique among the planets in the Solar System.

• Liquid water on the surface
  
  

• Atmosphere with oxygen
  
  

• Plate tectonics shaping land
  
  

• Magnetic field protecting from solar radiation
  
  

• Life exists
  

Continental drift

the idea that the continents were once together, but have since split apart (pangea)

what did Alfred Wegener discover?

saw that identical rocks could be found on multiple continents and could be matched up (pangea)

whats seafloor spreading?

the geological process at mid-ocean ridges where new oceanic crust forms from rising magma, solidifies, and then spreads outward, carrying continents apart in an ocean.

what does magnetic reversals indicate?

They indicate that the Earth is being torn apart along the ridges

(more evidence for Hess’ Seafloor Spreading)

What evidence did Wegener use for continental drift?

Matching rocks, mountain ranges, fossils across continents, and glacial features that aligned when continents were reassembled.

Why was continental drift not widely accepted at first?

Because people didn’t like the idea and there was no clear mechanism for how continents could move.

What is uniformitarianism?

The concept that Earth’s features can be explained by processes still observable today.

List the 5 main pieces of evidence for continental drift.

→ 1) Puzzle-like fit of continents
2) Matching rocks
3) Mountain ranges lining up
4) Similar fossils across continents
5) Glacial features lining up

What evidence supports seafloor spreading?

Underwater mountain ranges, youngest seafloor near ridges, magnetic reversals matching across ridges, GPS and earthquake data.

What generates Earth’s magnetic field?

Convection in the liquid outer core.

What is magnetic reversal?

The Earth’s magnetic field has switched between normal and reverse polarity over time.

What are Earth’s main layers?

Inner core, outer core, mantle, crust.

What are the two types of crust?

Oceanic (dense, 5–10 km thick)

Continental (lighter, 20–80 km thick).

Where does most earthquake and volcanic activity occur?

At plate boundaries (90%).

What drives plate movement?

Convection within the asthenosphere.

What is decompression melting?

When reduced pressure lowers the melting temperature of the mantle.

What forms at divergent boundaries?

Mid-ocean ridges and rift valleys; new oceanic crust forms as plates move apart.

What forms at ocean-continent convergent boundaries?

The denser oceanic plate subducts beneath the continental plate, forming a continental volcanic arc (e.g., Andes).

What forms at ocean-ocean convergent boundaries?

The older, denser plate subducts, forming a volcanic island arc (e.g., Japan, Philippines).

What forms at continent-continent convergent boundaries?

Large mountain ranges, such as the Himalayas.

What happens at transform boundaries?

Plates slide past each other, creating features like the San Andreas Fault, Salton Sea, and San Gabriel Mountains.

plate tectonics.

Plate tectonics is the theory that Earth’s lithosphere is broken into plates that move across the surface, driven by convection in the mantle.

What source of energy drives plate tectonics? How?

Heat from Earth’s interior causes convection currents in the asthenosphere, which move the lithospheric plates.

What is the general concept behind continental drift, and how does Hess’ seafloor spreading fit into it?

How does paleomagnetism provide evidence of seafloor spreading?

Continents were once joined and drifted apart. Seafloor spreading explains this by creating new crust at ridges that pushes continents outward.

: What are the general characteristics of each type of plate boundary?

• Divergent: Plates move apart, form new crust at mid-ocean ridges and rift valleys.

• Convergent: Plates collide; one may subduct, forming volcanic arcs, trenches, or mountains.

• Transform: Plates slide past each other, causing earthquakes and surface features like fault lines.

How does the mantle melt at divergent boundaries?

By decompression melting — as plates pull apart, pressure drops, lowering the melting point of mantle rock.

How does the mantle melt at convergent boundaries?

By hydration melting — water from the subducting plate lowers the melting temperature of the overlying mantle, causing magma formation.