Geology: Earth Structure, Plate Tectonics, Rocks, and Fossils

These flashcards cover the key concepts related to Earth's structure, tectonic plate movements, types of rocks, and fossil formation.

What are the concentric layers of the Earth?

Earth consists of the crust (granitic continental and basaltic oceanic), mantle (silicate minerals), and core (iron-nickel).

How does temperature change with depth in the Earth?

Temperature rises about 25–30°C per kilometer in the crust, then more gradually in the mantle.

What happens to pressure as depth increases in the Earth?

Pressure increases by roughly 30 MPa per kilometer, making deep rocks ductile and altering minerals.

What are tectonic plates?

Tectonic plates are rigid slabs of lithosphere that float on the asthenosphere and move slowly due to mantle convection.

What is the difference between convergent, divergent, and transform boundaries?

Convergent: plates collide; Divergent: plates separate; Transform: plates slide past each other.

What geological features are formed at convergent boundaries?

Convergent boundaries form subduction zones, volcanoes, and mountain ranges.

How do earthquakes relate to tectonic plate boundaries?

Earthquakes occur when stress at plate boundaries is released.

What is continental drift?

Continental drift is the theory proposed by Wegener that continents were once joined as Pangaea and have drifted apart.

What evidence supports the theory of continental drift?

Evidence includes identical fossils, rock types, and ancient climate patterns found on distant continents.

What are slab pull and ridge push?

Slab pull is the force that pulls a tectonic plate down at subduction zones; ridge push is the force that pushes plates apart at mid-ocean ridges.

What do fossil evidences indicate about continents?

Identical fossils found on distant continents indicate that those continents were once connected.

How did new evidence advance the acceptance of continental drift?

New data such as magnetic striping and GPS confirmed Wegener's idea of moving plates.

What are the three types of rocks?

Igneous, sedimentary, and metamorphic.

How do igneous rocks form?

Igneous rocks crystallize from magma.

What is the rock cycle?

The rock cycle consists of processes like weathering, erosion, deposition, metamorphism, and melting, transforming rocks.

What distinguishes intrusive rocks from extrusive rocks?

Intrusive rocks cool slowly underground, forming large crystals; extrusive rocks cool quickly at the surface, leading to fine textures.

How does cooling rate affect crystal size?

Slower cooling produces larger crystals, while faster cooling results in smaller or glassy textures.

What are minerals and ores?

Minerals are natural, crystalline solids with specific compositions; ores contain valuable minerals concentrated for extraction.

How can the relative age of fossils be determined?

Relative age can be determined by the law of superposition and the use of index fossils and cross-cutting features.

How do volcanoes relate to tectonic plate boundaries?

Volcanoes commonly form at convergent boundaries, where subduction occurs, and at divergent boundaries, where magma rises as plates separate.

How do metamorphic rocks form?

Metamorphic rocks form when existing rocks are subjected to intense heat and pressure, or chemically active fluids, causing them to change their mineralogy, texture, or chemical composition.

How do sedimentary rocks form?

Sedimentary rocks form from the compaction and cementation of sediments (weathered rock fragments, organic matter, or chemical precipitates) that accumulate over time in layers.

What geological features are formed at divergent boundaries?

Divergent boundaries form mid-ocean ridges, rift valleys, and new oceanic crust as tectonic plates pull apart.

What geological features are formed at transform boundaries?

Transform boundaries are primarily characterized by large strike-slip faults, such as the San Andreas Fault, where plates slide horizontally past each other, often causing significant earthquakes but little to no volcanic activity or mountain building.

How do the properties of rocks relate to their uses, and what are some examples?

Rocks are utilized based on their specific properties:

• Hardness and Durability: Granite and basalt are used as building materials, paving stones, and in construction due to their strength and resistance to weathering.

• Permeability: Sandstone and limestone can act as aquifers for groundwater storage due to their porosity.

• Aesthetic Appeal: Marble and slate are used for decorative purposes, such as countertops, flooring, and roofing, because of their appearance and ease of finishing.

• Chemical Composition: Limestone is crucial in cement production; certain clays are used in ceramics.

How can sedimentary layers be used to date past natural hazards?

Sedimentary layers can be used to date past natural hazards by analyzing distinct event deposits (e.g., turbidites from tsunamis/landslides, flood deposits, or paleo-seismites). Techniques such as stratigraphy (relative positioning of layers), radiocarbon dating of organic material within layers, and tephrochronology (dating volcanic ash layers) help determine the timing and frequency of these events, providing a historical record of hazards.

How can a mineral be classified based on its observable properties?

Minerals are classified based on distinct observable properties including:

• Hardness: Measured by its resistance to scratching, often using the Mohs scale.

• Luster: Describes how its surface reflects light (e.g., metallic, glassy, dull).

• Streak: The color of the mineral's powder when rubbed on an unglazed porcelain plate.

• Color: While sometimes unreliable due to impurities, it is a primary characteristic.

• Cleavage/Fracture: How the mineral breaks; cleavage is a tendency to break along flat parallel surfaces, while fracture is an irregular break.

• Crystal Form: The characteristic geometric shape of its crystals.

• Density/Specific Gravity: The ratio of the mineral's mass to the mass of an equal volume of water.

• Special Properties: Such as magnetism, reaction to acid, taste, or fluorescence.

How do rocks and minerals, particularly ores, contribute valuable resources?

Rocks and minerals provide essential valuable resources such as metals (e.g., iron, copper from ores), construction materials (e.g., granite, limestone), and energy resources (e.g., coal, uranium).

How are fossils formed?

Fossils are primarily formed when organisms are rapidly buried in sediment (like mud, sand, or volcanic ash) shortly after death. Over long periods, the soft tissues decay, but the hard parts (bones, shells, teeth) are replaced by minerals or leave an impression. The sediment then compacts and hardens into sedimentary rock, preserving the organism's remains or traces.

What is the full process of fossilization and its various mechanisms?

Fossilization typically begins with the rapid burial of an organism's remains in sediment, which protects it from scavengers and decomposition. The process then involves several mechanisms:

• Permineralization: Minerals from groundwater seep into porous spaces of hard tissues (like bones or wood) and crystallize, effectively turning them to stone.
• Replacement: The original organic material is completely dissolved and replaced by new minerals, retaining the original shape.
• Molds & Casts: If an organism (or part of it) dissolves after being buried, it leaves an empty space (a mold). This mold can later be filled with sediment or minerals, forming a cast.
• Compression/Carbonization: Organic material, like leaves or soft-bodied organisms, is flattened by overlying sediments, leaving behind a thin film of carbon.
• Unaltered Preservation: In rare cases, the original organism or parts are preserved without significant alteration (e.g., insects in amber, mammoths in ice, or organisms in tar pits).

Finally, the surrounding sediment compacts and hardens into sedimentary rock, encasing and preserving the fossilized remains or traces over geological time.