Planet Earth
Shape and Size of the Earth Gravity is what gives Earth its spherical shape Only effective if the body is of a critical size Critical radius is about 350 km
Shape and Size of the Earth Earth is not a perfect sphere but an oblate spheroid that bulges out at the equator Particles on a spinning object fly outward as a result of their inertia strongest force at the equator because it is spinning the fastest there 1000 mph at the equator, 700 mph at midlatitudes
Composition of the Earth Most common elements are oxygen, silicon, aluminum, magnesium, and iron (oxygen and silicon are usually found combined together as silicates) Earth s interior is mostly the mineral olivine and iron-magnesium silicate
Density of the Earth Density = mass/volume g/cm 3 Earth s mass = 6 X 10 21 metric tons or 6 X 10 27 grams Radius = 6400 km = 6.4 X 10 8 cm Volume of a sphere = 4/3 π R 3 So what is Earth s density? What does this number mean?
The Interior of the Earth How do we know what s inside when the deepest we have penetrated the Earth s surface is about 7 miles, a mere scratch in the surface We need indirect evidence Provided by seismic waves; speed of the waves is dependent on the type of material they are passing through
Using Seismic Waves S waves and P waves P waves can travel through both solids and liquids S waves can travel only through solids When an earthquake takes place the P waves pass directly through the center of the Earth, but the S waves are deflected indicating that there is a liquid portion to the core More complicated analysis can help determine the density of the material these waves are passing through and lead to clues to about their composition
Using Seismic Waves Seismic studies show that Earth s interior has four distinct regions 1. Crust 20 to 70 km rocks composed mostly of silicates 2. Mantle hot, but not quite molten composed of silicates mostly olivine extends roughly halfway to Earth s center capable of slow flow even though it is not molten 3. Outer core liquid, probably a mixture of iron, nickel, and perhaps sulfur 4. Inner core solid, probably iron and nickel Why solid?
Structure of the Earth Materials separate by density in a process called differentiation Takes place when a mixture of heavy and light material melts with the heavier materials sinking and lighter materials rising Scientists infer that this means that the Earth was completely molten at one time
Heating of the Earth s Core Near the surface temps rise about 2 K every 100 meters you descend (if this held true all the way to the center the temp would be 120,000 K The core is estimated to be about 6500 K Cooling from the outside Radioactive material present in all rocks radioactive decay releases energy in the form of heat Heat loss depends on surface area amount of heat contained depends on the volume
Heating of the Earth s Core Smaller bodies cool much quicker than larger one Heat gets trapped in Earth s interior causes the temperature to rise and rock to eventually melt
Age of the Earth Age of a rock can be determined by measuring the amount of radioactive material it contains Radioactive atoms decay into daughter atoms Uranium decays into lead Radioactive potassium decays into argon Oldest rocks ages to 3.6 billion years Rocks from the moon and other bodies have ages about 4.5 billion years
Movement in Earth s interior Convection heated matter becomes less dense and rises Plate tectonics rifting the spreading and breaking apart of the crust acts like a conveyor belt Subduction one piece of crust sinking of being pushed beneath another piece of crust Called continental drift or plate tectonics
Earth s Atmosphere Mostly Nitrogen (78%) and oxygen (21%) Early atmosphere likely was hydrogen, methane, ammonia, and water vapor (methane and ammonia are noxious poisons) Solar winds and UV radiation would have destroyed this early atmosphere Secondary atmosphere - Outgassing from volcanoes Comets hitting the young Earth
Earth s Atmosphere Over the past 3 billion years the amount of oxygen in our atmosphere has been increasing This rise in oxygen paralleled the development on life on our planet Most of the free oxygen we breath today came water in the photosynthetic process The rest comes water molecules being split by UV radiation
The Ozone Layer Some shielding of UV radiation comes from O 2, but most comes from Ozone O 3 Located about 25 km above the surface of the Earth Life probably couldn t exist without the ozone layer Control of ozone destroying chemicals
The Greenhouse effect Sunlight converted to heat at the Earth s surface Surface radiates infrared energy that is blocked by the atmosphere from returning to space This blocking makes the surface warmer than it would be without this blocking effect
The Greenhouse effect This does not generate heat, but merely keeps heat from being lost into space This infrared is absorbed by carbon dioxide and water vapor which is then re-emitted both into space and back to Earth Mars has carbon dioxide in its atmosphere but so little of it that it doesn t trap much heat Venus has a lot of carbon dioxide and traps a lot of heat Scientist prefer to use the term atmospheric effect
The Earth s magnetic field William Gilbert was the first to recognize that the Earth acted like a magnet (1603) The Chinese has used this idea hundreds of years earlier to invent the compass Magnetic lines of force the closer the lines the stronger the magnetic field Polarity gives field lines direction start at a north magnetic pole and end at a south magnetic pole
The Earth s magnetic field Generated by electric currents These currents are generated in Earth s molten iron core Scientists think they come from rotational motion and convection Earth s magnetic poles do no coincide with its axial poles The position of the magnetic pole changes slightly from year to year and even reverses polarity about every 200,000 years. These changes probably come from the irregular motion of the core
Effects of the Magnetic Field Screens us from charged particles emitted by the sun Aurora caused by these charged particles colliding with nitrogen and oxygen in the upper atmosphere Magnetosphere found at the top of the atmosphere where it controls the structure of the atmosphere Magnetosphere traps charged particles in two doughnut shaped rings called the Van Allen Radiation belts
Magnetosphere
Earth s motion The Seasons Coriolis effect air and ocean circulation also establishes the direction of the jet streams Precession - the very slow change in the direction that Earth s axis is pointing Precession wouldn t happen if the Earth were a perfect sphere One swing in about 26,000 years This will eventually mean Vega replaces the North Star (Polaris) as the one the North pole points toward (14,000 AD) Climate change