Introduction to Geology – Practice Flashcards

A comprehensive set of question-and-answer flashcards covering key concepts from the Chapter 1 Introduction to Geology lecture, including Earth structure, plate tectonics, volcanism, gradation, dating methods and the role of geology in civil engineering.

What is the literal meaning of the word “Geology”?

Geo means Earth and logos means discourse, so Geology is the discourse or study of the Earth.

Name the two broad branches of geology.

Physical geology and Historical geology.

Which branch of geology studies Earth materials and the processes acting on and within Earth?

Physical geology.

Which branch of geology examines Earth’s origin and evolutionary history?

Historical geology.

State one main learning outcome related to Earth’s divisions from Chapter 1.

Define the crust, mantle, outer core and inner core and describe their physical and chemical characteristics.

List the four principal divisions of Earth’s interior in order from surface to center.

Crust, mantle, outer core, inner core.

What is the average thickness range of continental crust?

About 30–100 km.

What rock type dominates continental crust?

Granite (Al-silicates).

What rock type dominates oceanic crust?

Basalt / Gabbro (Fe-Mg silicates).

How old is the oldest continental crust?

Up to about 4.1 billion years.

How old is the oldest oceanic crust?

Less than 200 million years.

Define lithosphere.

Rigid outer layer comprising the crust and the uppermost solid mantle.

Where is the asthenosphere located?

Below the lithosphere within the upper mantle; it is partially molten and ductile.

What causes lithospheric plates to ‘float’?

They are less dense and sit atop the weaker, partially melted asthenosphere.

Name the three main mechanisms that drive plate motion.

Ridge push, slab pull and mantle convection currents.

What theory first proposed a single supercontinent named Pangaea?

Continental Drift Theory by Alfred Wegener.

Approximately when did Pangaea begin to break apart?

About 200–250 million years ago.

Give an example of a divergent plate boundary on land.

East African Rift Valley.

Give a mid-ocean example of divergent boundaries.

Mid-Atlantic Ridge.

What forms at oceanic–continental convergent boundaries?

Volcanic arcs and trenches (e.g., Andes Mountains).

What is produced at oceanic–oceanic convergence?

Island arcs and deep trenches (e.g., Marianas Trench).

Name a continental–continental convergent boundary feature.

The Himalayan mountain range.

What type of boundary is the San Andreas Fault?

Transform plate boundary.

What is a tectonic ‘hot spot’?

A fixed zone of upwelling mantle plumes that form volcanic chains as plates move over them.

Give an example of a hot-spot volcanic chain.

Hawaiian Islands.

Define volcanism.

The process of magma and gases erupting through Earth’s crust to form volcanoes.

Name the six common volcano types.

Fissure, Shield, Dome, Ash-cinder (Cinder cone), Composite (Stratovolcano), Caldera.

Which volcano type has gentle slopes and is built by basaltic lava flows?

Shield volcano (e.g., Mauna Loa).

Which volcano is famous for forming a large caldera lake in Oregon?

Crater Lake (Mount Mazama).

What are the two main textures of basaltic lava flows?

Pahoehoe (ropy) and Aa (rough, blocky).

List three major materials emitted during volcanic eruptions.

Lava flows, pyroclastic debris (bombs, lapilli, ash, blocks), and volcanic gases (mainly H₂O, CO₂).

What is a pyroclastic flow?

A fast-moving current of hot gas and volcanic debris that rushes down volcano slopes, reaching ~200 km/h.

Define gradation in geology.

Combined processes of erosion, transport and deposition that wear down and build up Earth’s surface.

Distinguish between degradation and aggradation.

Degradation erodes and lowers land; aggradation deposits sediment and builds up strata.

What is weathering?

The breakdown and decomposition of rock at or near Earth’s surface.

Define erosion.

The movement of weathered material downslope or away from its source under gravity or transporting agents.

List five primary agents of erosion.

Running water, wind, ice (glaciers), waves, and gravity (mass wasting).

What is an alluvial fan?

A fan-shaped deposit of sediment formed where a stream exits a mountain front onto a flat valley floor.

Name two aeolian (wind-formed) depositional features.

Sand dunes and loess deposits.

What are the two main glacier types?

Alpine (valley) glaciers and ice sheets.

Describe glacial plucking.

Removal of rock fragments that freeze into the base or sides of a glacier and are carried away.

What is till?

Unsorted mixture of sediment sizes deposited directly by melting ice.

Define moraine.

A ridge or mound of till deposited by a glacier, marking its former edge.

What coastal feature forms when waves connect an island to the mainland?

Tombolo.

What is mass wasting?

Downslope movement of soil and rock under gravity without the aid of a transporting medium.

Give two examples of rapid mass-wasting events.

Rockfalls and debris slides/landslides.

What is soil creep?

Very slow, continuous downslope movement of soil and regolith.

Explain solifluction.

Slow flow of water-saturated soil over impermeable permafrost in cold regions.

What is the purpose of the geologic time scale?

To divide Earth’s 4.6 billion-year history into meaningful intervals based on major events.

Name the two fundamental dating approaches in geology.

Relative dating and absolute (radiometric) dating.

State the Law of Superposition.

In undeformed sedimentary layers, the oldest layer is at the bottom and the youngest at the top.

What is an unconformity?

A gap in the geologic record where rock layers were not deposited or were eroded away.

Define an angular unconformity.

Younger horizontal strata overlie older tilted or folded layers.

What does the Law of Cross-Cutting Relationships state?

Geologic features that cut through rocks are younger than the rocks they cut.

Explain the Law of Inclusions.

Rock fragments (inclusions) within a layer are older than the host rock containing them.

What are index fossils and why are they useful?

Fossils of organisms that lived briefly but widely; they help correlate rock layers of the same age.

Which radioactive isotope is commonly used to date recent organic remains?

Carbon-14.

Define half-life.

The time required for half of the atoms of a radioactive isotope to decay to its daughter product.

Which isotope pair is frequently used to date very old rocks?

Uranium-238 to Lead-206.

What role does geology play in site investigation for civil engineering?

It assesses soil, rock, groundwater and hazards to inform design and construction safety.

Why is understanding foundation geology critical for engineers?

It determines bearing capacity and stability, guiding selection of suitable foundation types.

Give an example of how geology influences material selection in construction.

Presence of expansive clay may require special concrete mix or soil stabilization techniques.

How can geological knowledge mitigate landslide risk during earthworks?

By identifying unstable slopes and designing proper drainage, slope angles and retaining structures.

List the four principal Earth ‘spheres’.

Atmosphere, hydrosphere, lithosphere, biosphere.

What gases dominate Earth’s atmosphere?

Approximately 78 % nitrogen and 21 % oxygen.

Describe two geologic functions of the atmosphere.

Absorbs harmful UV radiation and drives weathering via temperature and moisture variation.

What is the hydrosphere?

All water on Earth in oceans, lakes, rivers, groundwater, glaciers and atmosphere.

Name three processes that move water between hydrosphere stores.

Evaporation, precipitation, infiltration (others include runoff, condensation, groundwater flow).

Define lithosphere in the context of Earth’s spheres.

The rigid, inorganic rock layer forming continents and ocean floors.

What is the biosphere?

The global system encompassing all living organisms and their interactions with Earth’s other spheres.

Which plate has the largest surface area on Earth?

The Pacific Plate.

Which plate boundary type is associated with seafloor spreading?

Divergent plate boundaries.

What surface expression often marks a transform boundary between continental plates?

A linear fault zone, such as the San Andreas Fault.

What volcanic hazard involves super-heated ash clouds racing downslope?

Pyroclastic flow (nuée ardente).

Which erosion agent creates loess deposits?

Wind (aeolian processes).

Name two shoreline depositional features produced by wave action.

Spits and barrier islands (others: bay-mouth bars, tombolos, cuspate forelands).

What is the Big Bang Theory’s relevance to geology?

It explains the origin of the universe, leading to stellar and planetary formation, including Earth.

State one characteristic that distinguishes inner from outer planets.

Inner planets are rocky and solid; outer planets are primarily gaseous/icy.

What is the prevailing model for Solar System formation?

Collapse of a spinning nebular disk about 5 billion years ago forming the proto-Sun and proto-planets.