Earth’s Layers The three main layers of Earth are the crust, mantle, and the core. These layers vary greatly in size, composition (what they are made of), temperature, and pressure

Earth’s Layers

Earth’s layers Geologists have used two main types of evidence to learn about Earth’s interior: Direct evidence from rock samples Indirect evidence from seismic waves which are waves made by earthquakes Seismic waves show that Earth is made up of layers like an onion.

Earth’s Layers Crust: the outermost layer Mantle: middle layer Core: inner layer Temperature and pressure increase as you move from the crust to the core

Earth’s Layers Crust: a layer of solid rock that includes both dry land and the ocean floor. Thinnest layer, 5-70 km thick Continental crust is thicker than oceanic crust, but less dense Oceanic crust is more dense than continental crust, but way thinner

Earth’s layers Mantle: made up of rock that is very hot, but mostly solid. Scientists divide the mantle into layers based on the physical characteristics of those layers. Layer below the crust. Thickest layer, about 3,000 km thick Top of mantle is called the lithosphere. Middle layer of the mantle is the asthenosphere Bottom layer is called the lower mantle.

Core: made mostly of the metals iron and nickel. Earth’s Layers Core: made mostly of the metals iron and nickel. Has two layers: outer core, made of liquid metal(High pressure, but so hot it stays liquid) inner core, solid metal(Pressure overcomes heat and keeps this solid)

Conduction/Radiation Conduction: Heat transfer within a material or between materials that are touching. Ex: spoon in pan of hot soup becoming too hot to touch. Radiation: The transfer of energy through space. No direct contact needed Ex: the Sun or an open flame

Convection Currents Convection = the transfer of heat by movement of particles in fluids. Heat from the core and the mantle itself causes convection currents in the mantle. As parts of the mantle heat up, they become less dense and rise towards the top. As mantle cools it becomes more dense and with the help of gravity it sinks back down.

Convection currents Convection currents in the mantle move very slowly. They are responsible for plate tectonics Convection currents in the core result in Earth’s magnetic fields. When the heat source is removed, convection currents eventually stop.

Plate Tectonics Continental Drift: continents move slowly over Earth’s surface. Idea proposed by Alfred Wegener. He said that all the continents were once joined together in a single landmass, called Pangaea, and have since drifted apart.

Plate Tectonics Wegener used evidence to support his idea: For example: West side of Africa and the east side of South America look like matching puzzle pieces. Mountain ranges in Africa and South America line up as if they were once part of the same mountain range. Plant fossils found in rocks in Africa, South America, Australia, India, and Antarctica. Paleoclimatic evidence – Example: Proof of ancient glaciers in Australia

Plate Tectonics Wegener could not explain the force that pushes and pulls the continents, so most geologists did not accept his ideas.

Sea-floor spreading: sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them. Sea-floor spreading slowly adds new rock to the ocean floors. Proposed by Harry (H.H.) Hess

Seafloor Spreading Several types of evidence supported Hess’s theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and 3. the ages of the rocks themselves. (youngest at midocean ridges and oldest near deep ocean trenches).

Seafloor Spreading In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches. Subduction is the process of the rocky crust bending downward into the mantle. Sea-floor spreading and subduction work together. They keep the ocean floors moving like conveyor belts.

Plate Tectonics Theory of Plate Tectonics: Pieces of Earth’s lithosphere are in slow, constant motion driven by convection currents in the mantle. Explains the formation, movement, and subduction of Earth’s plates. It also explains the formation of mountains, volcanic mountain ranges, and volcanic island arcs.

Boundaries Wherever plates meet, called a plate boundary, you usually find volcanoes, mountain ranges or deep-ocean trenches.

Boundaries There are three kinds of plate boundaries: divergent boundaries, convergent boundaries, and transform boundaries.

Boundaries Divergent boundary is where two plates move apart. Divergent boundary between two ocean plates forms a mid-ocean ridge, between two continental plates forms a rift valley.

Boundaries Convergent boundary is where two plates push together. A convergent boundary between two oceanic plates forms a deep-ocean trench and volcanic island arcs A convergent boundary between two continental plates forms a mountain range. A convergent boundary between an oceanic and continental plate forms volcanic mountains (volcanoes)

Boundaries Transform boundary is where two plates slide past one another. Earthquakes occur at a transform boundary. Example: San Andreas