Earth’s History and Structure View of Earth from moon. We know what the surface of the Earth looks like. What does the inside look like?

Do Now What are the main compositional layers of the Earth?

Crust Mantle Core

Origin of the Earth Earth formed approximately 4.6 billion years ago Early earth lacked an atmosphere Meteors and Asteroids bombarded the Earth Our early Earth grew from a barrage of extraterrestrial impacts, increasing in mass over time. In the early stages of planetary accretion, the Earth was much less compact that it is today. The accretionary process led to an even greater gravitational attraction. Gravitational energy converted into heat. Radioactive elements are unstable, and over time become more stable. Radioactive decay processes releases heat. U-238 to Pb-206. Initial accretion led to a homogeneous sphere that eventually became density stratified with the heavier iron and nickel sinking to the center of the earth, and the lighter silicates (rocky) floated to the top.

Meteor Crater Arizona

Earth’s Interior Core Mantle Crust Made of Iron and Nickel Inner Core - solid Outer Core - liquid Mantle Less dense than core Iron and Silicates Mostly solid Core – composed of two parts. The core is very dense and composed mostly of Iron and Nickel. The inner core is solid. This is because there is so much pressure exerted that it can only exist in the solid form. The outer core is liquid iron and nickel. Again, it is very dense but because it is in its liquid form it is less dense than solid and forms the outer core. Mantle is composed of Iron and Magnesium silicates (Si + O). It is mostly solid, but the uppermost part of the mantle is partially molten (slush – where you do have liquid and solid mixed). Now, this is very important in plate tectonics. Crust –This is the outermost layer. It is very thin and rigid. Rigid means that it is a solid. If you can imagine an apple. It would have the thickness of the skin of an apple. There is two types of crust – continental crust and oceanic crust. Important notes: Thin crust + uppermost mantle is rigid. This forms the “lithospheric plates”. partially molten mantle acts as a lubricant. This enables the plates to move freely along the surface of the Earth. Crust Outermost layer is solid rock. Continental – granite Oceanic – basalt

Lithosphere The outer solid layer of the Earth Litho- Rock Sphere- Round

Lithosphere Consists of continental, oceanic and upper part of mantle Continents composed of granite-type rock, less dense then oceanic crust Oceanic crust formed of basalt; more dense then continental crust Why do continents sit higher than ocean basins? It is their composition and density. Continent = Quartz (SiO2) and Feldspars (K, Ca, Na, Al, SiO2). These are light elements. Ocean = Basalt (Fe and Mg). These are heavier elements. Asthenosphere is partially molten. It forms a lubricant to allow plates to move.

Asthenosphere Located below the Lithosphere Enormous heat and pressure Rock exhibits Plasticity: ability to flow Causes Tectonic Plates to move

Mesosphere Located below the Asthenosphere “Meso” means middle

Outer Core Made of liquid Iron and Nickel

Inner Core Made of solid iron and nickel

Do Now What is the difference between the Earth’s lithosphere and asthenosphere.

Earth’s Gravity Gravity is the force of attraction due to an object’s mass Determined by mass and distance between two objects in space

What is the difference between weight and mass? Hint: You would weigh less on the moon, but your mass is constant.

Weight and Mass Weight-Measurement of the pull of gravity on an object Mass-The amount of matter an object is composed of

Classwork/Homework Research how the Earth’s magnetic field is generated. Describe how the magnetic field protects us from radiation.

Classwork/Homework Read 29-32 Define all Key Terms Answer (1-6) on pg. 32

Earth’s Interior

Continental Drift Evidence Researchers noted geographic fit of continents e.g. Africa and S. America Atlantic formed by separation of Africa from S. America Seuss, 1885, proposed super continent by studying fossils, rocks, mountains Wegener and Taylor, early 1900’s, proposed continental drift and Pangaea Seuss hypothesized a super continent “Pangaea” surrounded by oceans. Evidence supporting the idea that the continents had drifted. Geographic fit of continents Fossils Mountains Glaciation

Continental Drift Geographic Fit About 210 Ma, Pangaea began to break apart. Continents seem to fit together like pieces of a puzzle

Continental Drift Fossils Studies were done on land animals that could not swim. Once continents split, evolution occurs. Organisms begin to differentiate. Climate is different, food sources are different, predators are different. Similar distribution of fossils such as the Mesosaurus

Palisades in North New Jersey

Continental Drift Mountains If you were to put the puzzles back together, mountain chains match up, i.e., Appalachian Mtns, British Isles, and Caledonian Mtns. Mountain ranges match across oceans

Continental Drift Glaciation Glaciers typically occur near the poles. We are in a warm period, but in the past it was cool and ice caps grew. Deposits related to glaciers were deposited. You also find glacial deposits in Africa near the equator. How to you get glacial deposits near the equator? Glacial ages and climate evidence

Diving between the plates in Iceland

Continental Drift Model Problems Alfred Wegener Presented research to professionals Did not provide a plausible mechanism to explain how continents drifted Wegener was a scientist. Scientists go to scientific meetings to present their research. When Wegener presented his research to other physicists, they did not agree. They wanted to know how do continents drift? There was no driving mechanism to support continental drift. Wegener could not answer “how” so his Continental Drift Model was not accepted.

Seafloor Spreading Continental drift reexamined in 1960’s with new information New theory developed – Seafloor spreading Supporting evidence for seafloor spreading World seismicity Volcanism Age of seafloor The 1960’s is relatively recent. Geology is a new science compared to Physics, Chemistry and even Biology. People were doing separate studies about earthquakes, volcanoes, age of sea floor, paleomagnetism. Someone put it all together. A new theory developed – Seafloor Spreading. There were a lot of evidence to support Seafloor spreading. Paleomagnetism Heat flow Theory combining continental drift and seafloor spreading termed “Plate Tectonics”

Seafloor Spreading The idea of seafloor spreading is that new crust is being formed at spreading centers and old crust is being destroyed in deep trenches. For example, Mid-Atlantic ridge is a chain of underwater mountain chains where new crust is being formed. New sea floor created at the mid-ocean ridge and destroyed in deep ocean trenches

Evidence for Seafloor Spreading World Seismicity Note: Orange is shallow. At spreading centers, EQ only occur at the surface. At SZ, deep EQ occur, i.e. Japan, Indonesia, Philippines, Aleutians. How does seismic activity support plate tectonics? They occur along plate boundaries. Earthquake distribution matches plate boundaries

Evidence for Seafloor Spreading Volcanism Where do volcanoes occur? Subduction zones. Why are they associated with subduction zones? Oceanic crust is moving deep into the Earth. Volcanism also occur at hot spots. Where is the tallest mountain? Mauna Loa. Highest elevation? Mount Everest. If you were to take Mauna Loa and place next to Mount Everest, it is the highest mountain. It is measured at its base deep on the ocean floor. Volcanoes match some plate boundaries; some are hot spots

Evidence for Seafloor Spreading Age of Seafloor Age of Earth is 4.5 Ga. Oldest oceanic crust is only 180 Ma. Why is the ocean so young? Old oceanic plate is being subjected or destroyed. Youngest sea floor is at mid-ocean ridge Oldest sea floor away from mid-ocean ridge

Evidence for Seafloor Spreading Paleomagnetism Today, Earth’s magnetic field points to the North. Why? They believe that the magnetic field is caused by the liquid outer core moving around the solid inner core by Earth’s spin. The iron (Fe) content in the core produces a magnetic field. Magnetic field is important to us in that it prevents harmful radiation of the Sun to reach us. Every 700,000 years or so, the Earth’s magnetic field reverses. These reversals are recorded in molten magma. As the magma cools, its iron-rich minerals tend to line up with Earth’s magnetic north. Earth has a magnetic field - Probably caused by rotation of solid inner core in liquid outer core (both mostly Fe) When rocks cool at the Earth’s surface, they record Earth’s magnetic field (normal or reverse polarity)

Evidence for Seafloor Spreading Paleomagnetism The record of these alternating reverse and normal polarity helps support the idea of seafloor spreading. Paleomagnetic studies indicate alternating stripes of normal and reverse polarity at the mid-ocean ridge.

Seafloor Spreading Heat Flow

Seafloor Spreading Convection Currents Magma was found were new seafloor was being made. In 1960, proposed as driving force to move continents

Theory of Plate Tectonics Heat flow provided the mechanism to move the lithospheric plates. John Tuzo Wilson combined ideas of continental drift and seafloor spreading into “Plate Tectonics”

Principles of Plate Tectonics Earth’s outermost layer composed of thin rigid plates moving horizontally Plates interact with each other along their edges (plate boundaries) Plate boundaries have high degree of tectonic activity mountain building earthquakes volcanoes

Plate Boundaries Three types There are three ways that plates can move relative to each other. They can move apart – divergent plate boundary, they can come together – convergent boundary, or they can slide past one another – transform fault. Divergent Convergent Transform

Plate Boundaries Divergent Plates move away from each other New crust is being formed

Divergent Plate Boundaries Examples East African Rift Mid-Atlantic Ocean Ridge

Plate Boundaries Convergent Three Types: Ocean-continent Ocean-ocean Continent-continent Plates are moving toward each other Crust is being destroyed

Convergent Plate Boundaries Examples Mount Fuji, Japan Mount Lassen, California Andes, South America

Plate Boundaries Transform xxxxxxxxxxxxxxxxxxx Crust is neither created nor destroyed Plates slide past one another

Transform Plate Boundaries Examples San Andreas Fault Calexico, California Carrizo Plains, Central California