 The four terrestrial planets all have similar internal features:  Dense, metallic core  Less dense, solid/plastic mantle  Low-density, solid crust

 Earth is believed to have formed about 4.6 BYA from the solar nebula.  Along with the other Terrestrial planets, Earth passed through 4 developmental stages: 1. Differentiation 2. Cratering 3. Flooding 4. Slow Surface Evolution

 Recall, differentiation, the separation of material according to density, is believed to have occurred due to melting of Earth’s interior.  Heat generated from radioactive decay and energy released from in-falling matter.

 The heavy bombardment occurred about 4 BYA and made craters on Earth and other Terrestrial planets.  Magma flooded large basins and when the environment cooled, water fell as rain and flooded them as well.  Continuing surface evolution has existed over the past 3.5 billion years has constantly re- shaped the surface of the Earth (geologic processes along with weathering/erosion).

 Earth’s crust is composed into several distinct pieces, which are in constant motion with respect to each other and this process is known as plate tectonics. Evidence of this is found on the ocean floor … … and in geologically active regions across the Pacific.

 Where plates move toward one another, they can be pushed upward or downward  convergent plate boundary.  Formation of mountain ranges, presence of volcanic activity and/or earthquakes.  Where plates move away from each other, magma can rise up, producing volcanism  divergent plate boundary.

Hot spots  result of magma penetration through holes in tectonic plates (Hawaii formation)

 About 1 BYA, the supercontinent Rodinia, meaning “motherland”, existed.  Most landmasses were gathered south of the equator.

 About 450 MYA, after Rodinia broke up, Earth’s continents were separated as they are today.

 The continents had joined back together around 200 MYA in the supercontinent Pangaea, meaning “all Earth”.  Certain mountain ranges formed, including the Appalachians.

 When Pangaea split apart, it eventually separated into a northern piece (Laurasia) and a southern piece (Gondwanaland) around 150 MYA.

 About 50 MYA, the continents continued their separation, resembling their current-day locations.  India collided with Eurasia  Himalaya Mountain formation.

 Believed if plate movements continue at current rates, in 150 million years, Africa will collide with Eurasia, closing off Mediterranean Sea.  New subduction zones will form, closing off the Atlantic as well.

 A new supercontinent, Pangaea Ultima, will form in approximately 250 million years.

 Surface formations visible today have emerged only very recently compared to the age of Earth.

 High temperature and tremendous pressure in Earth’s interior make any direct exploration impossible.  Exploration possible because earthquakes produce vibrations called seismic waves, traveling through the interior of the Earth.  Register on sensitive detectors called seismographs all over the world.

 Two main types of seismic waves:  Body – seismic waves traveling through the body of a medium (fastest-moving seismic wave category).  P waves  S waves  Surface – seismic waves traveling along the surface of a body rather than through the middle of it (slowest- moving seismic wave category; most destructive).  Rayleigh waves  Love waves

 Body waves traveling through solids and liquids are called P waves.  “Primary” waves  “Pressure” waves  Fastest moving seismic wave.  Avg. speed in crust = 6.1 km/s  Particles of rock move in a back-and-forth direction.

 Body waves traveling through only solids are called S waves.  “Secondary” Waves  “Shear” Waves  Second fastest seismic wave.  Avg. speed in crust = 4.1 km/s  Particles of rock move in an side-to-side direction.

 Rayleigh waves are surface waves causing the ground to move with an elliptical, rolling motion.  Love waves are surface waves causing the ground to move with a side to side motion perpendicular to the direction of the traveling wave.

 The P and S waves (body) caused by an earthquake do not travel in straight lines or at constant speeds within the Earth.  May reflect off boundaries between the layers of different density, or they may be refracted as they pass through a boundary.  Such information can be analyzed to infer the structure of Earth’s interior.

 Earth’s interior gets hotter towards the center.  Earth’s core is as hot as the Sun’s surface; metals are liquid. Solid crust Solid mantle Liquid core Solid inner core Melting point = temperature at which an element melts Melting point increases with increasing pressure towards the center - Reason inner core becomes solid

 Earth’s core consists mainly of Iron (Fe) and Nickel (Ni)  Both have high electrical conductivity.  The rotation of the convecting, conducting liquid (outer core) generates Earth’s magnetic field in a process called the dynamo effect.  Same process that generates the solar magnetic field in the convective layers of the Sun.

 Earth’s magnetic field protects it from the solar wind (ionized gases).  The surface of the magnetic field where the solar wind is first deflected is called the bow shock.  The region where Earth’s magnetic field dominates is called the magnetosphere.  High-energy particles from the solar wind leak into the magnetosphere and become trapped within Earth’s magnetic field and produce belts of radiation known as the Van Allen belts.

As high-energy particles leak into the lower magnetosphere, they excite molecules near the Earth’s magnetic poles, causing the auroras.

 Earth once had a primeval atmosphere composed of gases captured from the solar nebula during the formation of Earth (H, He, CH 4 ).  Composition was severely altered, eventually led to a secondary atmosphere  through 2 main processes: 1.Outgassing: release of gases in Earth’s interior through volcanism. During a volcanic eruption, 50-80% of the gas released is water vapor. The rest is CO 2, Nitrogen, and small amounts of sulfur gases. 2.Later bombardment with icy meteoroids and comets.

 The ozone layer exists in the second layer of Earth’s atmosphere, the stratosphere.  Composed of 3 oxygen atoms linked together, O 3.  Absorbs (is opaque to) ultraviolet radiation from the Sun, protecting life on Earth’s surface.

 Earth’s surface is heated by radiation from the Sun.  Heat energy is re-radiated from Earth’s surface as infrared radiation.  CO 2 makes the atmosphere less transparent to infrared radiation (more opaque).  Just as glass is opaque to infrared radiation in a greenhouse.  Thus, heat is trapped due to CO 2 through a process known as the greenhouse effect.

 The Greenhouse Effect occurs naturally and is essential to maintain comfortable temperatures on Earth.  However, human activity may be increasing the concentration of greenhouse gases through CO 2 emissions (cars and industrial plants) and deforestation through what is known as global warming.

 The amount of warming to expect in the future is difficult to predict because Earth’s climate is critically sensitive to a number of different factors, not just the abundance of greenhouse gases.  For example, a planet’s albedo is the fraction of sunlight hitting it that gets reflected away.  Albedo of 1 = WHITE  Albedo of 0 = BLACK  Earth’s albedo is about 0.39  39% of sunlight hitting it reflects back to space.

 Chlorofluorocarbons (CFC’s), used in industrial processes, refrigeration, and air conditioning destroy the ozone layer (which absorbs UV radiation).  Destruction of the ozone layer proven  ozone hole over Antarctica.

Dear People, Keep me like this! Sincerely, Earth