Hon Environmental Science THE DYNAMIC EARTH NOTES. Scientists divide the Earth into 4 parts or spheres. What are these spheres? 1. geosphere 2. atmosphere 3. hydrosphere 4. biosphere Now, describe each sphere: 1. Geosphere: solid part of the earth that consists of all rock, as well as the soil and loose rocks on Earth s surface. Most of the geosphere is located in Earth s interior. 2. Atmosphere: mixture of gases that makes up the air we breathe. Most of the gases are found in the first 30km above Earth s surface 3. Hydrosphere: all of the water on or near Earth s surface. Much of this water is in oceans. Also found in atmosphere, on land in soil 4. Biosphere: area on earth where life exists. Made of parts of geosphere, atmosphere and hydrosphere. THE GEOSPHERE 1
The composition of the Earth: Scientists divide Earth into three layers, based on their composition or chemical make up. These layers are composed of progressively denser materials toward the center of the Earth. These are known as compositional layers. The 3 layers are the crust, the mantle, and the core. Describe each of the core layers below: 1. Crust: 2. Mantle: 3. Core 5-70 km thick Solid, brittle outermost layer of Earth Continental crust is thicker (20-70km thick) and made of lightweight materials, while oceanic crust thinner (5-8km thick) and made of denser materials Makes up less than 1% of earth s mass Earth s thinnest layer Layer beneath crust 64% of mass of Earth 2900 km thick Made of iron-rich and dense rocks Composed of densest elements 3400 km thick radius Sphere of hot, dense nickel and iron a center of Earth The Structure of the Earth If we consider the physical properties of each layer, instead of their chemistry, the Earth is divided into 5 layers, called the physical layers. These layers are the lithosphere, asthenosphere, mesosphere, outer core and inner core. 1. lithosphere: Earth s outer layer Cool, rigid 15 300 km thick Consists of crust and uppermost mantle Divided into huge pieces called tectonic plates, which move around on top of the asthenosphere and can have both oceanic and continental crust 2
2. asthenosphere : Layer of the mantle just beneath the lithosphere and above mesosphere Plastic, solid layer of mantle made of rock that flows very slowly, allowing tectonic plates to move on top of it 25 km thick 3. mesosphere: Lower part of the mantle, between asthenosphere and outer core 2550 km thick Aka middle sphere 4. outer core: 2200 kkm thick, a dense liquid layaer Outer shell of Earth s core Made of liquid nickel and iron 5. Inner core : A sphere of solid nickel and iron at the center of the Earth Solid because under enormous pressure 1228 km radius, 4000 5000 degrees Celsius Label the 3 compositional layers Label the 5 physical layers 3
The Theory of Plate Tectonics Earth used to be made up of a super-continent called Pangea, and all the surrounding seas were called Panthalassa. The Earth s lithosphere is divided into pieces called tectonic plates. These plates glide across the underlying asthenosphere in much the same way as ice glides across a pond. The continents are located on tectonic plate and move around with them. The major tectonic plates include the Pacific, North American, South American, African, Eurasian, and Antarctic plates. (see text p. 66) Plate Boundaries The area where 2 plates meet is called a plate boundary. 3 Main Types of Plate Boundaries and Land Features They Create: 1. Divergent- plates spread apart; move away from each other. This causes earth quakes and volcanic activity. Land features created: rift valleys and mid ocean ridges Example: Mid Atlantic ridge North American Plate Eurasian and African plates 2. Convergent-plates move towards each other and collide. Three types of convergent boundaries: a. Oceanic plate & Oceanic plate - Cause earthquakes and trenches Indian Eurasian 4
b. Oceanic plate & Continental plate- Cause earthquakes and volcanic activity c. Continental plate & Continental plate Cause earthquakes, volcanic activity and mountains Example: Himalayas 3. Transform-plates slide past each other causing Earthquakes Example: San Andreas Fault, CA Pacific Plate North American Plate The major tectonic plates 5
EARTHQUAKES A fault is a break in the Earth s crust along which blocks of the crust slide relative to one another. When rocks that are under stress suddenly break along a fault, a series of ground vibrations is set off. So, an earthquake is a series of vibrations of the Earth s crust caused by slippage along a fault. Earthquakes occur all the time, but most are so small we don t feel them Earthquakes can be enormous and cause a great deal of damage. Richter scale used by scientists to quantify amount of energy released by earthquake Magnitude amount of energy released Smallest magnitude felt = 2.0; largest recorded = 9.5! Magnitudes of 7.0 or greater cause major damage Each increase in magnitude represents 31.7X more energy than the number below it Where do earthquakes occur? Most take place near plate boundaries. VOLCANOES A volcano is a mountain built from magma (melted rock) that rises from the Earth s interior to its surface. They often located near tectonic plate boundaries (convergent or divergent) and can occur on land or under sea, where they can eventually form islands When do volcanoes erupt? When pressure of magma inside becomes so great, it blows open the solid surface of the volcano Some volcanoes have magma flowing out of them all the time, so the pressure never builds up and never erupt Effects of volcanic eruptions Can be local or global Clods of hot ash, dust and gases can flow down the slope really fast and burn everything in their path During an eruption, volcanic ash can mix with water and produce a mud-flow Ash that falls to the ground can cause buildings to collapse, bury crops and damage the engines of vehicles Volcanic ash can cause breathing difficulties Eruptions can change Earth s climate for several years volcanic ash and sulfur-rich gases can reach the upper atmosphere and reduce the amount of sunlight that reaches the Earth s surface *Note: While plate movement brings rock to the surface and alters the Earth s surface, rocks at the Earth s surface can be altered by wind and water as well. 6