Earth Earth is the planet that we know best Our observations of the other planets are all compared to the conditions and properties of Earth Properties of Earth Semimajor Axis Orbital Eccentricity Orbital Period Rotation Period Mass Radius Average Density Surface Gravity Surface Temperature Atmosphere 1 A.U. 0.017 365.2422 days 23 hrs 56 min 5.976 x 10 24 kg 6378 km 5.5 g/cm 3 9.80 m/s 2 ~300K 78% Nitrogen, 21% Oxygen The interior of the Earth remains one aspect of our planet that we cannot directly observe Earth's Interior The details of the Earth's interior are revealed through indirect methods such as seismic and volcanic activity 1
Revealing the Interior We cannot directly see the interior of the Earth, but we can observe and detect the affect it has on the surface Volcanoes reveal that the interior of the Earth must be hot enough to produce liquefied rock or magma Seismic Waves A P-wave is a pressure wave where material is compressed and 'squeezed' as the wave passes A S-wave is a side to side motion of the material as the wave passes P-waves can travel through both solids and liquids, while S- waves cannot travel through liquids Mapping the Interior When an earthquake occurs, the shaking, however small, can be detected at stations all over the Earth Each station can monitor the type of waves that reach it Sights closer to the epicenter receive both P and S-waves, while sites further away only receive P-waves 2
Current Interior Model From detailed seismological studies, the current model for the interior includes an inner and outer core, the mantle, and the crust The inner core is a very hot and dense solid, while the outer core is liquid The mantle makes up most of the Earth's volume and is made up of warm semi-fluid rock Why Such a Hot Core? When the Earth was still forming, it was constantly bombarded by large objects Each impact released lots of heat and energy into the Earth, causing it to remain molten in its early life Also, radioactive decay of uranium and other elements in the Earth's interior add another source of heat Because the young Earth was completely molten, it allowed materials to differentiate over time Differentiation The heavier denser elements such as nickel and iron sank to the core, while the light elements, like silicate rocks, rose to the surface 3
Surface Activity The consequences of a molten interior do not go unnoticed on the surface Tectonic Plates These plates are made of less dense material than the mantle, and therefore 'float' on the surface Convective motion in the mantle causes these plates to move over time When plates collide, one plate will usually sink into the mantle while the other raises higher, forming mountains Plate Motion San Andreas Eurasian Fault Plate California A subduction zone is a location where a plate is being forced into the interior Mariana Trench Pacific Ocean Indian Plate Where two plates are spreading apart, new material from the mantle rises up from below 4
Geological and fossil evidence tells us that the continents have moved great distances over time Continental Drift This is enough time for the continents to have separated from one large land mass called Pangaea Magnetic Record in the Crust Material rising up from the mantle (mainly iron) will orient itself based on the Earth's magnetic field Evidence shows that the Earth's magnetic field has changed direction repeatedly, on average every 500,000 years What Creates the Magnetic Field? We do know that moving charged material creates a magnetic field The spinning core of the Earth contains charged material and is believed to form the Earth's magnetic field 5
The Magnetic Field Magnetic field lines extend outward from the north and south magnetic poles and surround the Earth The Van Allen Belts As the charged particles from the solar wind encounter the magnetosphere, some become trapped The outer belt contains mainly electrons, while the inner belt contains the heavier protons Aurorae These particles excite gases high in the atmosphere, producing a brilliant color display If the Earth had no magnetosphere, it would be constantly bombarded by these particles, making it much harder for life forms to survive 6