Earth's Interior

• Earth's interior has layers (in relation to depth)
• Different layers of Earth's interior have different depths, densities, pressures, temperatures, state of matter (solid/liquid), and composition
• Convection cells (aka convection currents) occur in Earth's interior
• Features on Earth are formed due to plate tectonics
• Earth's structure: crust at the top (oceanic and continental), mantle in the middle (uppermost -- rigid, asthenosphere -- "plastic", and lower -- stiffer), and the core at the center of Earth (outer and inner)
• Oceanic crust is thinner than continental crust, is made of basalt (which is mafic in composition), and is more dense (3.0 g/cm3)
• Continental crust is very thick (thickest under mountains), is made of granite (felsic composition), and is less dense (2.7 g/cm3)
• The lithosphere consists of the crust and the uppermost mantle
• The asthenosphere is partially melted ("plastic"), and it allows for movement of the plates due to convection currents resulting from density differences
• Convection currents in the mantle are caused by transport of heavier elements towards the center of earth (frictional heating, mostly at a steady state now), and nuclear decay (releases energy, accounting for 50% of Earth's internal heat). Convection currents are NOT caused by pressure pushing down on itself
• The lithosphere "floats" on top of the asthenosphere, and makes up plates
• The outer core is liquid
• The inner core is solid due to extreme pressure
• The outer core was discovered because earthquake waves didn't arrive as expected (were changed/stopped)
• Changes in earthquake waves velocities gave evidence of a boundary between the inner and outer core
• Meteorites formed in the early solar system and represent early solar system materials
• Alfred Wegener proposed the theory of continental drift -- a theory that the continents shifted position on Earth's surface. He wasn't taken seriously because he couldn't provide a mechanism for what caused continental drift.
• Evidence for continental drift included the "puzzle-fit" shapes of the continents, similar fossils found on different continents, rock/mountain formations that were similar on different continents, and climate change evidence such as glaciers, coal, and coral reefs
• Plate tectonics is the theory that describes the formation, movements, and interactions of Earth's lithospheric plates (includes continents)
• Plate tectonics provides evidence for new crust formation, location of volcanoes and earthquakes, and mountain building -- all of which are concentrated around plate boundaries
• Strains build up and release around plate boundaries, causing earthquakes
• Molten rock rises (usually) at plate boundaries, forming volcanoes (ex. the Ring of Fire)
• Crust folds and reforms at plate boundaries, causing mountain building
• Igneous rocks on the ocean floor provide evidence for plate tectonics because new seafloor forms and seafloor spreading occurs due to new igneous rocks forming at ocean ridges
• In 1948, Marie Tharp (at Lamont Doherty Earth Observatory), organized sonar data for ocean depth (collected by Heezen). She made a topographic map of the sea floor (Atlantic Ocean), and discovered the Mid-Atlantic ridge (a rift valley) where seafloor is spreading apart -- a divergent plate boundary
• Igneous rocks on the ocean floor provide evidence for plate tectonics because the rocks in the center of oceanic ridges are the youngest and hottest (bc magma is erupting), and as they move outward, they get older and colder (bc they had time to cool)
• Igneous rocks on the ocean floor provide evidence for plate tectonics because the direction of Earth's magnetic field (normal and reversed polarity) is "recorded" in the rocks as lava solidifies and magnetic minerals align with the magnetic field. This forms "mirror image" bands/"magnetic stripes". The current orientation is "recorded" at the ridge center because that's where new rock is forming
• The distribution of earthquakes and volcanoes (mostly at plate boundaries where they interact) provides evidence for plate tectonics
• Continental and ocean floor features such as mountains, volcanoes, faults, and trenches provide evidence for plate tectonics
• Divergent plate boundaries are where plates move away from each other
• Convergent plate boundaries are where plates move towards each other
• Transform plate boundaries are where plates slide past each other
• The 2 types of divergent boundaries are oceanic and continental
• Divergent plate boundaries are constructive because the lithosphere is formed
• Examples of oceanic divergent boundaries are the Mid Atlantic Ridge and the East Pacific Rise
• Oceanic divergent plate boundaries create a mid-ocean ridge, cause seafloor spreading, oceanic crust (mainly from dense basalt) forms as rock cools, and due to differences in the rate of spreading, the crust is broken into sections offset from each other by breaks (fracture zones) that are perpendicular to the ridge. This is a source of earthquakes
• Earthquakes at divergent plate boundaries are shallow
• A rift valley is the center of a ridge
• Seafloor spreading occurs due to convection currents, as magma pushes up through cracks
• Rock closer to a ridge is younger, and rock farther from a ridge is older, because older crust is pushed away from the ridge center as new crust is formed