The Earth. Overall Structure of Earth

Transcription

1 The Earth Why Study The Earth??? It s our home! Where did life come from, where is it going. To understand the other planets. Study of other planets will, in turn, help us understand the Earth. Overall Structure Atmosphere Interior Surface activities Magnetic Field Tides Magnetosphere ~ 20,000 km Overall Structure of Earth Atmosphere ~350 km Interior ~6400 km Crust or Hydrosphere ( 5 to 50 Km) 1

2 Atmosphere Air is a mixture of gases: nitrogen - 78% oxygen - 21% argon % carbon dioxide % water vapor % Earth s Atmosphere 2

3 Convection Convection causes surface winds and the weather that we experience. Also produces turbulence in the air and that s why Aero-planes tend to fly at the top of the troposphere. Greenhouse effect 3

4 Atmosphere: Effects of Solar Radiation The Solar UV radiation is absorbed by ozone (O 3 ) - provides protection for life on Earth A small amount of optical radiation is scattered by the air molecules blue is scattered more efficiently than red - blue skies and red sunsets (due to air molecules and dust) Heat from the surface causes convection (up and down circulation) in the atmosphere. Convection produces surface winds, weather and the turbulence in the air. Solar optical radiation is absorbed by the Earth s surface and reradiated in the Infra-red. Some of Earth s IR radiation gets trapped by H 2 0 or CO 2, which heats the air further (greenhouse effect). Earth s green house effect makes our planet almost 40 K hotter than would otherwise be the case. - increase in CO 2 over time leads to hotter Earth Origin of Earth Atmosphere Primary atmosphere: hydrogen, helium, methane, ammonia and water vapors. Secondary atmosphere: methane, carbon dioxide, sulfur dioxide and components containing nitrogen. Solar UV rays decomposed the lighter hydrogen rich gases into hydrogen and then hydrogen escaped into the space. Carbon dioxide and sulfur dioxide condensed dissolved in oceans and rocks. Life appeared in the oceans more than 3.5 billion years ago and organisms eventually began to produce Oxygen. 4

5 Internet sites for animation Seismic waves: Earths interior: Earth s Interior We cannot drill the Earth s surface more than a few kilometers. How can know about its interior??? You know, most disastrous phenomena. EARTHQU QUACKS can be used to study the interior of our home Earth. 5

6 Seismic waves An earthquake --- causes the entire planet to vibrate a little. These vibrations are not random rather systematic, called seismic waves. Two waves of particular importance are: P-waves These are first to arrive at monitoring station (primary waves) These are pressure waves just like sound waves. Speed 5-6 km/s. Can travel through both solids & liquids. S-waves Arrive at some time later (secondary waves) These are shear waves just like waves in guitar string. Speed 3-4 km/s. Cannot travel through liquids. The speed of both P- and S-waves depend on the density of the matter through which they travel. Hence, by measuring the time taken for the waves from the site of an earthquake to one or more monitoring stations, we can determine the density of matter in the interior, in addition to the information about Earthquake. Liquid (iron, nickel) T ~ 4600 k D ~ kg/m 3 ~1300 km ~ 3000 km ~ 2200 km ~ 5 to 50 km Granite-rich rocks T ~ 300 K D ~ kg/m 3 Solid (Iron, nickel) Temperature ~ 5000 k Density ~ kg/m 3 Pressure ~ 4 millions times the atmospheric pre at Crust. Silicate rocks (silicon & oxygen) T ~ K D ~ kg/m 3 Upper mantle: iron-magnesium -silicates (basalt) 6

7 Earth s Interior (results from seismic waves) The Earth s interior shows differentiation variation in structure and composition with distance from center. Earth was molten rock in the past (~ 4.6 billion yrs ago) - higher density material (iron, nickel) sank to the core. - lower density material (silicates, etc.) rose to surface Crust: Cooled-off outer surface, continental plates Mantle: soft silicate rocks, plus magma (liquid silicates) Outer Core: liquid metals (iron, nickel) Inner Core: solid metals (due to pressure from overlying regions Earth s Magnetosphere The region around a planet that is influenced by that planet s magnetic field is called magnetosphere. Earth s magnetic field is Like a bar magnet with North and South poles. These magnetic poles are roughly aligned with Earth s spin axis with a tilt of 11.5º. Poles are not fixed, they drift at a rate of 10 km/ year. Northern Canada (Center of North America) Latitude ~ 80 º N N S Antarctica (south of Australia) Latitude ~ 60 º S 7

8 Van Allen Belts (Two doughnut shaped high-energy particle zones at 3,000 km and 20,000 km above Earth surface.) Magnetic Field Effect Earth s magnetic field exerts control over charged particles (ions) by herding them into the Van Allen Belts. - protects us from harm by fast ions from Sun. Aurora borealis or Northern Lights Escaping particles from the Van Allen Belt, intersect with Earth s atmosphere near the north and south pole, produce spectacular light show called aurora. Aurora australis or Southern Lights 8

9 Shape of Earth s Magnetic Field 10 Earth Radii Even beyond moon The magnetic field is continuously generated by liquid metal outer core and exists only because Earth is rotating. (Dynamo theory) The Tides Tides are the periodic variations in the surface water level of the oceans, bays, gulfs, and inlets. At most coastal locations on the Earth, there are two high tides and two low tides each day. Tides also differ in height on a daily basis. Tides exhibit daily, monthly and yearly cycles. 9

10 What causes the tides? Tides are the result of the gravitational attraction of both the sun and the moon on the earth. The sun is ~ 400 times further from the earth than the moon. So, the attraction of the moon is far greater than the attraction of the sun due to the close proximity of the earth and the moon. The daily differences between tidal heights is due to the changing distance between the earth and the moon. Tides (looking from above the NP) Start with a spherical Earth (including oceans), and there is no Moon or Sun. But moon is there revolving around the Earth. You get tides. Now let the earth rotate underneath the oceans. - high tides every 12 hours -friction carries the oceans along a little -increases orbit of the Moon - decreases the Earth s rotation 10

11 The Sun also affects tides - ½ tidal force of the Moon Long-Term Effects of Tides In the past: - Earth s rotation was 22 hours (a year had ~ 400 days) - Moon s orbit was smaller - Moon s rotation was not tidally locked to Earth In the present: - Moon is tidally locked (one lunar orbit = one lunar day) -- reason why we see only one face of Moon In the future: - Earth will be tidally locked to Moon (Moon will remain at fixed location in sky) -Moon s distance from the Earth would be 550,000 Km ( about 43% greater than present) 11

12 Spring and neap tides animation: 12