Earth's Age, Plate Tectonics, and Rock Processes: A Comprehensive Geology Review

What is the estimated age of the Universe?

Approximately 13.8 billion years.

How was the age of the Universe calculated?

Using the expansion rate, cosmic microwave background measurements, and models of Big Bang nucleosynthesis.

What is the estimated age of the Earth?

Approximately 4.54 billion years.

What method is primarily used to date the Earth?

Radiometric dating, especially U-Pb / Pb-Pb isochrons.

What is the estimated age of the Moon?

Approximately 4.50 to 4.51 billion years.

What process led to the formation of Earth's layers?

Differentiation, where molten iron sank to form the core and lighter silicates rose to form the mantle and crust.

What is the composition and density of continental crust?

Density ~2.7 g/cm³, solid, composition: felsic to intermediate (granite), thickness ~30-70+ km.

What is the composition and density of oceanic crust?

Density ~3.0 g/cm³, solid, composition: mafic basalt/gabbro, thickness ~5-10 km.

What is the lithosphere composed of?

The crust (oceanic or continental) and the rigid uppermost mantle.

What is the asthenosphere and its properties?

The upper mantle below the lithosphere, density ~3.3-4.5 g/cm³, solid but mechanically weak and ductile.

What is the outer core's state and its role?

Liquid (iron-nickel alloy) that convects to generate Earth's magnetic field.

What evidence did Alfred Wegener provide for continental drift?

Jigsaw fit of continents, matching fossil assemblages, matching rock units, and paleoclimatic indicators.

What discoveries in the mid-20th century supported plate tectonics?

Mapping of the sea-floor, magnetic striping, and age patterns of oceanic crust.

What are the three types of plate boundaries?

Divergent, convergent, and transform boundaries.

What occurs at divergent plate boundaries?

Plates move apart, leading to mid-ocean ridges and new oceanic crust formation.

What is a characteristic feature of convergent plate boundaries?

Plates move together, leading to features like deep trenches and volcanic arcs.

What happens at transform plate boundaries?

Plates slide past one another horizontally, resulting in strike-slip faults and earthquakes.

What is the behavior of continental lithosphere at boundaries?

Resists subduction, tends to crumple and form mountain belts upon collision.

What is the density difference between oceanic and continental lithosphere?

Oceanic lithosphere is denser (mafic) and sits lower, while continental lithosphere is less dense (felsic) and floats higher.

What is the approximate density of the inner core?

Density estimates range from 12.8 to 13.1 g/cm³.

What is the role of convection in Earth's mantle?

It drives the movement of tectonic plates and the cooling of outer layers.

What is the significance of the giant-impact hypothesis for the Moon's formation?

It suggests the Moon formed shortly after Earth's formation due to a massive collision.

What is the major driver of tectonic plate movement?

Slab pull, where cold, dense subducting slabs sink into the mantle, pulling the trailing plate.

What mechanism involves gravitational sliding at mid-ocean ridges?

Ridge push, which helps drive plates away from the ridges.

How does mantle convection contribute to tectonic plate movement?

Slow convective flow in the mantle exerts drag on the base of plates, with upwelling at ridges and downwelling at subduction zones.

What are the five characteristics that define a mineral?

1. Naturally occurring, 2. Inorganic, 3. Solid at Earth's surface conditions, 4. Definite chemical composition, 5. Ordered internal atomic structure.

What is the order of crystallization in Bowen's Reaction Series?

High-temperature ultramafic minerals crystallize first (e.g., Olivine), followed by lower temperature minerals (e.g., Quartz).

What type of lithosphere is primarily composed of mafic minerals?

Oceanic lithosphere, which is low in silica and leads to effusive eruptions.

What type of eruptions are associated with continental lithosphere?

Explosive eruptions due to higher viscosity magmas, often resulting in stratovolcanoes.

How can hotspot chains be used to determine plate movement?

By measuring the distance from an active volcano to older volcanoes in the chain and dividing by the age difference.

What volcanic behavior is typical of oceanic hotspots?

They produce low-viscosity basalt leading to shield volcanoes and effusive flows.

What is the difference in igneous rock formation at divergent versus convergent plate boundaries?

Divergent boundaries produce mostly basalt, while convergent boundaries produce andesite to rhyolite suites.

What does grain size and texture in igneous rocks indicate?

It indicates the cooling history: slow cooling leads to large crystals (phaneritic), while fast cooling leads to small crystals (aphanitic).

What are the two types of weathering that lead to sedimentary rock formation?

Physical (mechanical) weathering breaks rocks into clasts, while chemical weathering alters minerals and liberates ions.

What sedimentary rock is formed from quartz grains accumulating in transport?

Quartz sandstone, formed from mechanical and chemical weathering.

Which mineral is the most susceptible to chemical weathering according to Bowen's order?

Olivine, which is more susceptible than other minerals like quartz.

What is the result of very rapid cooling of magma?

A glassy texture, as seen in obsidian.

What type of eruptions are associated with large igneous provinces (LIPs)?

Massive outpourings of low-viscosity basalt leading to significant climate effects.

What is the significance of the continuous branch in Bowen's Reaction Series?

It shows the evolution of plagioclase composition from calcium-rich to sodium-rich as temperature decreases.

What is the texture of igneous rocks that cool slowly underground?

Phaneritic texture, characterized by large crystals.

What type of volcanic activity is typical of continental hotspots?

They can produce highly explosive rhyolitic eruptions and basaltic products.

What is the role of slab suction in tectonic plate movement?

It contributes to the movement of tectonic plates at subduction zones.

What happens to sediment as it is transported farther from its source?

Grain size decreases, shape becomes more rounded, composition becomes dominated by quartz, and maturity increases.

What are the characteristics of conglomerate rocks?

Coarse (>2 mm), poorly sorted, rounded clasts; composed of mixed rock fragments; found in high-energy environments like alluvial fans and braided rivers.

Describe arkose sandstone.

Sand-sized with significant feldspar content, less mature; typically found proximal to the source in environments like alluvial fans near steep terrains.

What defines quartz sandstone?

Well-sorted and dominated by quartz; commonly found in beaches, dunes, and long-transport fluvial/shoreline environments.

What are the characteristics of shale?

Fine clay/silt, fissile; typically found in low-energy environments such as deep marine settings, lagoons, and floodplains.

What is limestone composed of and where is it typically deposited?

Composed of CaCO₃, often bioclastic or chemical; deposited in warm, shallow marine environments like carbonate platforms.

What is rock salt and how is it formed?

An evaporite mineral formed from the evaporation of restricted basins, such as arid coastal sabkhas and evaporitic lakes.

How is coal formed?

From compressed organic plant material (peat) in swampy, anoxic, low-energy coastal or fluvial wetlands.

What does transgression indicate in sea level changes?

A rising sea level relative to land, characterized by a fining upward sequence where coarser shoreface deposits are overlain by finer offshore muds.

What does regression indicate in sea level changes?

A falling sea level, shown by a coarsening upward sequence where offshore muds are overlain by nearshore sands and terrestrial deposits.

Define metamorphic rock.

Rock formed from a preexisting parent (protolith) through solid-state changes in mineralogy and texture under altered temperature, pressure, and chemically active fluids.

What processes are involved in metamorphism?

Recrystallization, neocrystallization, pressure solution, phase changes, mineral alignment (foliation), and growth of index minerals.

What is contact metamorphism?

Metamorphism due to high temperature from igneous intrusion, resulting in non-foliated rocks like hornfels and marble.

What characterizes regional metamorphism?

Occurs during mountain building with high pressure and temperature over broad areas, leading to foliation and the formation of index minerals indicating increasing grade.

What is shock metamorphism?

Metamorphism caused by high pressure and temperature from meteorite impact, characterized by planar deformation features and high-pressure minerals.

What does the presence of index minerals indicate in metamorphic rocks?

They constrain pressure-temperature conditions and metamorphic grade.

What is the typical progression of metamorphism from shale?

Shale → Slate → Phyllite → Schist → Gneiss, indicating increasing heat and pressure.

How does tectonics affect crust thickness?

Continental collision thickens crust while rifting thins it.

What is isostasy?

The principle that thicker crust floats higher and forms roots, leading to isostatic compensation.

How do compressive stresses affect crustal thickness?

They shorten and thicken the crust, leading to folding, thrust faulting, and mountain building.

What is the effect of tensional stress on the crust?

It stretches and thins the crust, causing normal faulting and the formation of rift valleys.

What are volcanic mountains and how do they form?

Mountains built by repeated eruptions, typically found at subduction zones and hotspots.

What are fold mountains and how do they form?

Mountains formed by compressional collision, leading to folding and thickening of the crust.

What are fault-block mountains?

Mountains created by extension and normal faults, where blocks uplift as horsts.

What is the long-term evolution of mountains?

Uplift and erosion reduce relief and redistribute material, with sediments deposited elsewhere, and isostatic rebound causing uplift as mass is removed.