Plate tectonics
There is a theory that in the early days of the planet Earth, the continents were not as it is today, but before that was in one big piece, called Pangaea. Theorists propose that the continents became as it is today after slowly separating from each other. This theory is called Continental Drift. Another theory that supports the continental drift theory is the Plate Tectonics Theory. This theory suggests that pieces of the lithosphere, known as plates, move slowly on top of the asthenosphere .
These two are verified because geologists have found fossils of sea creatures on top of mountain ranges, suggesting that these mountain ranges were once part of the sea. Features of the Underwater plates Mid-Ocean Range: The Mid-Ocean Range is a chain of underwater mountains, which extends into all of the Earth’s oceans. It is the longest mountain chain on the crust. Sea-floor Spreading: The process in which new oceanic crust is created at mid-ocean ridges as older crust moves away. When old crust moves away, magma spews up and solidifies to form a new crust Subduction is a phenomenon where old oceanic plates sink into the mantle. This phenomenon occurs in subduction zones. This forms a trench, a depression within the ocean that forms after the plate sinking into the subduction zones. Subduction destroys old oceanic crust at subduction zones. Tectonic plate movement is caused by mantle convection of internal heat. Recall that mantle convection occurs by: Source 1: The heat that is the remainder from the extremely hot primal Earth Source 2: Radioactive Alpha Decay of the isotopesPlate Boundaries: Types of Plate Boundaries: Tectonic plates move together and forms ocean ranges and new lands. Divergent Boundaries: When plates that move away from each other. Magma rises to fill in the gap created from this motion and forms a new rock. Convergent Boundaries: Plates collide to each other.The denser plate slides under the other one to form a landmass. Transform Boundaries: The plates slide against each other. No creation/destruction of rocks are present. Mountains are formed along plate boundaries.The collision of the Indo-Australian and Eurasian plates produced the Himalayas. |
Phenomena from the platesEarthquakes:
A movement of the Earth’s lithosphere that occurs when the rocks in the layer suddenly shift, releasing stored energy Energy is carried by seismic waves. Most earthquakes are concentrated along plate boundaries. Stress: Stress is a force that squeeze, stretches, pushes and pulls rocks together. As tectonic plates move, they cause stress. Fault: A rupture in a mass of rock along which movement occurs. The San Andreas Fault is an example of a fault. Fold: A bend in the layers of rock. Forms where rocks are squeezed together. Rocks tend to fold rather then break, under high temp. or pressure Earthquakes occurs because stress forces have exceeded the strength of rock. Focus: The originated point of an earthquake, beneath the surface The epicenter is used to describe the location right above the focus, on the surface Any material has a limit to the stress absorption capacity. When rocks break, potential energy is transformed into kinetic energy through seismic waves. Seismic Waves: Seismic wave analysis has made geologists understand further more about the layers of the Earth P-Waves (primary waves): Longtitudinal waves that compress and expand the ground. Fastest seismic waves, and can travel through solid and liquid medium. S Waves (Secondary waves): Transverse waves that are slow, and cannot travel through liquid medium Surface Waves: Waves that develop when Seismic waves reach the surface. Slower than P Waves, but unleashes larger ground movements and more damage. Acts much like mechanical waves: When they touch a surface seismic waves diffract, reflect and refract. Geologists can make inferences based on wave motion Outer core is liquid, because S Waves cannot travel through it. The core is composed mostly of iron, because P-waves travel through the speed that matches waves passing through iron. Volcanoes Volcano is a mountain with a crater. It is one of the methods liquid reaches surface. Magma rises because it is less dense than the solid rock around and above it. As magma approaches the surface, low pressure allows gases to expand rapidly. Eruption occurs when gas bubbles out through a crack in the crust. Structure of a volcano: Magma chamber: Pocket where magma is accumulated Pipe: a vertical channel where magma passes to rise to the surface Vent: opening in the ground magma escapes to the surface Crater: the open pit of the central vent Caldera: Depression created after an eruption at the hollow shell of the empty vent Types of Eruptions: Quiet Eruptions: Usually done by volcanoes that have a very hot, low-silica magma. Lava erupts in a lava flow. Produce 2 types of lava: Pahoehoe: Hot, fast-moving lava with a ropelike surface Aa: Slow, cool lava with a chunky appearance Explosive Eruptions: Usually done by high-silica magma. Thick magma clogs the pipe, causing enormous pressure buildup. When explodes, lava and hot gases are hurled outward. Lava solidifies quickly, and chucks can vary in size. Volcano types and locations: Most volcanoes occur along plate boundaries, or hot spots. Hot spot: a region where hot rock extends from deep within the mantle to the surface Three types of volcanoes: Shield Volcano: Produced from quiet eruptions. Wide and flat. Cinder Cone: Caused by eruption with ash and cinders; small, steep-sided volcano Composite Volcano: Formed from explosive eruptions; A combination of lava and ash Igneous features: Formed by magma Batholith: Largest type of igneous rock mass. Can form mountain ranges. Sill: A result of magma hardening from cracks between rock layers. Dike: A magma crack cutting across rock layers, hardening afterwards. Volcanic Neck: When magma hardens in a volcanic pipe |