Topic 3: Tectonics

Plate Tectonics

The theory that the Earth’s outer shell is divided into several rigid plates that glide over the mantle (the asthenosphere), moving relative to each other

Mesosphere

The middle sphere made of solid mantle

Asthenosphere

The “weak” sphere made of mantle that is plastic-y

Lithosphere

A “rocky” sphere composed of the outermost 100 km of the Earth’s layers; it includes rigid crust and upper mantle

Continental Drift

The idea that the continents were once all together and they slowly drifted apart

Evidence For Continental Drift

A puzzle-like fit of continental margins, distribution of land/freshwater fossils, distribution of mountain-range/rock types, distribution of glacial features indicating the direction of the ice flow

Alfred Wegener

Hypothesized that the continents were once joined as a supercontinent called Pangea (“all Earth”), 300–240 MYA

Marie Tharp

Created the first map of the Atlantic seafloor, discovering the Mid-Atlantic Ridge (using new sonar technology developed in WW2)

Harry Hess

Proposed the idea of seafloor spreading in 1960

Seafloor Spreading

A process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge

Divergent Plates

Where two plates move apart, spreading centers, constructive margins; passive upwelling of the mantle associated with a decrease in pressure and melting and partial melting of ultramafic mantle material produces mafic melts

Convergent Plates

Where two plates move together, destructive margins

Transform Plates

Where two plates slide past each other in a horizontal or strike-slip motion, conservative margins, can occur in oceanic or continental crust

Mantle Convection

Rising magma at ocean ridges may push plates away from each other

Slab-Pull

Lithosphere breaks, sinks into the asthenosphere, dragging the plate away

Slab-Push

New rock produced at ocean ridges is less dense and rises above the seafloor; gravity pulls this plate downslope, pushing the entire plate away

Late Heavy Bombardment (LHB)

A hypothesized event occurring 4.1 to 3.8 Ga, where a disproportionately large number of asteroids and comets collided into the terrestrial planets and their natural satellites in the inner Solar System

Partial Melt

The geological process where some, but not all, minerals in a rock melt due to heat, pressure reduction, or the addition of a flux, creating a magma with a different composition from the original rock

Differentiation

A result of initial heating of Earth and a large, dense metallic core (Fe, Ni, S) overlain by a rocky silicate mantle, and a crust with an average thickness of 50 km up to 125 km on Mars

Noachian Period (4.1 to 3.7 Ga)

During this period, Mars’ surface was marked by meteor impacts, valley formation, erosions, and the possible presence of oceans and flooding by liquid water

Hesperian Period (3.5-3.3 to 2.9 Ga)

During this period, Mars was dominated by widespread volcanic activity forming huge lava plains

Amazonian Period (3.3-2.9 Ga to present)

During this period, Mars was marked by erosion from wind, with few impact craters; Olympus Mons formed during this period, with lava flows elsewhere on Mars