Alta High Astronomy Chapter 7 Earth: Our Home in Space

Alta High Astronomy Earth’s average density is around 5500 kg/m 3.  The water that makes up much of Earth’s surface has a density of 1000 kg/m 3  The rock beneath us on the continents, as well as on the seafloor, has a density in the range 2000–4000 kg/m 3.  This simple measurement allows us to make a very important deduction about the interior of our planet: It must be very dense compared to the surface features.

Alta High Astronomy Earth’s Structure Moving from the Inside Out  Inner Core – 1300 Km  Outer Core – 2200 KM  Mantle – 2900 KM  Crust 5 – 50 km – solid + hydrosphere.

Alta High Astronomy Atmospheric Structure Atmosphere –  Troposphere – Below 12 Km –  Stratosphere - Above 12 to about 50 Km  Mesophere – 50 – 80 Km  Ionosphere – Above 80 km  Magnetosphere – High above our atmosphere.  Troposphere – is where convection occurs due to surface heating, this gives us wind.  Ozone layer is between the stratosphere and the mesosphere – this protects us from much ultraviolet radiation.

Alta High Astronomy What Causes the Wind? Wind is caused by Convection, which is defined as the mass movement of particles. Solar heating of the air causes it to become less dense, hence warm air rises, and the denser, colder air falls to take its place. This causes what we call wind.

Alta High Astronomy What about that Atmosphere? How did the Atmosphere Form?  Primary atmosphere – mostly hydrogen and helium escaped when the earth was hot.  Secondary atmosphere – outgassed by volcanic activity which gave us water vapor which created the oceans when the planet cooled. Greenhouse effect  Most sunlight reaches the surface, which reradiates the energy.  Energy is trapped by atmosphere since it is effectively absorbed by water and Carbon dioxide.  Increase carbon dioxide, which absorbs infrared radiation effectively causes the atmosphere to heat up.

Alta High Astronomy Seismic Waves: Our Guide to the Interior We have learned much about the interior of the earth from seismic waves. These waves, caused by earthquakes and the shifting of the tectonic plates come in two varieties:  Primary or Pressure waves (P- waves) – are the first to radiate from an earthquake, they are longitudinal in nature, i.e. the amplitude of the wave is parallel to the wave motion  Secondary or Shear Waves (S-Waves) arrive later, these are transverse in nature, i.e. the amplitude of the wave is perpendicular to its motion.

Alta High Astronomy Seismic Waves: Our Guide to the Interior We learn about the earth’s interior by tracking the seismic waves through it The way that the wave is bent tell us the density of the material it is moving through.

Alta High Astronomy So How did the Earth Get this Way? Differentiation – Occurred as the earth cooled. This has to do with more dense materials falling to the center. Plate tectonics – the geological study of the plate system that makes up the earth’s surface. Plates make up the lithosphere which takes in the crust and the top part of the mantle. Plates ride on a semi-solid part of the mantle called the asthenosphere.

Alta High Astronomy What Drives the Plates? What drives the plates? Conduction warm rock rises pushing aside cooler rock – causing plate motion. Plate collision result either in  mountain ranges when you have uplift  trenches when you have a subduction zone – one plate goes under the other and returns to the mantle.

Alta High Astronomy Tides – Caused by the gravitational pull of the sun and the moon. Water is pulled toward the moon causing a high tide. Additionally, the solid portion of the earth is also pulled toward the moon leaving a bulge on the opposite side of the earth. High tides occur on both sides of the planet hence you high tide twice a day approximately every 12 hours. m/hsw/10000-the-moon-tides- video.htm m/hsw/10000-the-moon-tides- video.htm

Alta High Astronomy Spring and Neap Tides When the sun and moon are aligned on the same side you get a higher than normal tide called a spring tide. When the are on opposite sides you get a lower than normal tide called a Neap tide.

Alta High Astronomy Earth’s Other Atmospheric Protection: The Magnetosphere The Magnetosphere is a magnetic field which surrounds the earth. It consists of two doughnut shaped fields called the Van Allen Belts. It protects the earth from harmful electromagnetic radiation and the buildup of electric charge which could discharge to the earth

Alta High Astronomy How Does the Magnetic Field Protects Us? The Sun is a highly charged plasma which occasionally “flares up” and constantly emits charged particles in the direction of the earth. This “solar wind” travels through space and comes to earth where it encounters the Magnetic field. The electrically charged particle follow the field to the earth’s poles where they discharge. Creating the auroras. Without the magnetic field, the charged particles would build up in the atmosphere and randomly discharge, much like lightning, only stronger.

Alta High Astronomy What Causes a Magnetic Field? It is theorized that the earth’s magnetic field is caused by its “rapidly” spinning, molten, iron core. This “dynamo” effect creates the magnetic field which surrounds the earth. This is known as the dynamo theory of magnetism and is replicated by electrical generators which use a rapidly spinning loop of wire to generate electricity. Magnetic fields always accompany electric fields.