Earth Interior Crust Hydrosphere Atmosphere Magnetosphere Tides
Semi-major Axis 1 A.U. Inclination 0 Orbital period 1.000 tropical year Orbital eccentricity 0.017 Rotational period 23 h 56 min 4.1 s Tilt 23 27 Radius Mass 6378 km 5.97 x10 24 kg Bulk density 5.52 g/cm 3 Atmosphere N 2, O 2 Albedo 0.40 Surface temperature Escape speed 250-300 K 11.2 km/s Magnetic moment (equator) 8 x 10 10 G.km 3
The Early History of Earth Earth formed 4.6 billion years ago from the inner solar nebula. Four main stages of evolution: Two sources of heat in the Earth s interior: Gravitational potential energy of infalling material Decay of radioactive materials Most traces of early bombardment (impact craters) are now destroyed by later geological activity
Overall Structure of the Earth Atmosphere Hydrosphere (oceans) Thin, layered crust Mantle also divided into layers Two-part core (solid and liquid)
Earth s Interior What can we know about the Earth s interior from its mass and size? Earth s Mass = M Earth = 5.97 x 10 27 g Earth s Radius = R Earth = 6.378 x 10 8 cm Earth s Volume = V Earth = 4/3 π R 3 = 1.1 x 10 27 cm 3 Earth s Average Density = ρ Earth = M Earth /V Earth = 5.49 g/cm 3 ρ Water = 1 g/cm 3 ρ Rock = ~3 g/cm 3 ρ Iron = 7 g/cm 3 Cannot be made mostly of water Cannot be made mostly of rock Can be rock on the outside and iron on the inside A planet that has dense material in the interior and light material on the outside is said to be differentiated. Differentiation occurs when the whole planet is molten.
Earth s Interior Seismic waves are used to explore the Earth s interior: Earthquakes produce both pressure (P) and shear (S) waves Pressure waves will travel through both liquids and solids Shear waves will not travel through liquid, because liquids do not resist shear forces Wave speed depends on the density of the material and modulus of elasticity
We can use the pattern of reflections during earthquakes to deduce the interior structure of Earth. Earth s Interior
Earth s Interior Currently accepted model.
Earth s Interior The mantle is much less dense than the core The mantle is rocky; the core is metallic iron and nickel The outer core is liquid; the inner core is solid, because of pressure Some volcanic lava comes from the mantle allowing us to analyze the composition of the mantle nearest to the surface (the upper mantle)
Earth s Interior History: Earth was probably molten when it formed then the upper layers solidified and later remelted because of bombardment by space debris. Heavier materials sank to the center. Radioactivity provides a continuing source of heat.
Crust and Upper Mantle Continental drift or plate tectonics: The entire Earth s surface is covered with crustal plates, which can move independently Earthquakes and volcanoes occur at plate boundaries
Plate Tectonics Crustal plates move with respect to each other. Where plates move toward each other, plates can be pushed upward and downward formation of mountain ranges, some with volcanic activity, earthquakes Where plates move away from each other, molten lava can rise up from below forming new crust volcanic activity
Plate Tectonics A plate colliding with another can also raise it by folding it, resulting in very high mountains Active Examples: Himalayas Alps Inactive Example: Appalachians
Plate Tectonics Plates can also slide along each other, creating faults where many earthquakes occur Example: San Andreas Fault
Plate Tectonics Plate motion is driven by convection in the upper mantle. Mantle material in this zone is a very viscous liquid like glass
Plate Tectonics The new crust created at rift zones preserves the magnetic field present at the time it solidified. From this, we can tell that magnetic field reversals occur about every 500,000 years.
Earth s Tectonic History
Volcanism on Earth Volcanism on Earth is commonly found along subduction zones (e.g., Coast Range in California). This type of volcanism is not found on Venus or Mars.
Shield Volcanoes Found above hot spots: Fluid magma chamber, from which lava erupts repeatedly through surface layers above. All volcanoes on Venus and Mars are shield volcanoes
Shield Volcanoes Tectonic plates moving over hot spots producing shield volcanoes a chain of volcanoes Example: The Hawaiian Islands
Radioactive Dating The number of protons (atomic number) in an atom s nucleus determines which element it is. However, there may be different isotopes of the same element, with the same number of protons but different numbers of neutrons. Many of these isotopes are unstable and undergo radioactive decay. This decay is characterized by a half-life T: Fraction of material remaining = (1/2) t/t
Radioactive Dating Half-lives have been measured in the laboratory for almost all known isotopes. Knowing these, we can use them to determine the age of samples by looking at isotope ratios. The most useful isotope for dating rock samples is 238 U, which has a half-life of 4.5 billion years, comparable to the age of the Earth. The dating process involves measuring the ratio between the parent nucleus and the daughter nucleus ( 206 Pb in the case of 238 U) The Sun and planets should have about the same age. Dating of rocks on Earth, on the Moon, and meteorites all give ages of ~4.6 billion years.
History of Geological Activity Surface formations visible today have emerged only very recently compared to the age of Earth.
Hydrosphere About 2/3 of Earth s surface is covered by water. Mountains are relatively rapidly eroded away by the forces of water. Water makes life possible on Earth
Surface Heating: Sunlight that is not reflected is absorbed by Earth s surface, warming it Surface reradiates as infrared thermal radiation The atmosphere absorbs some infrared, causing further heating, thus warming the troposphere this is called the greenhouse effect Earth s Atmosphere
The blue curve shows the temperature at each altitude The troposphere is where convection takes place responsible for weather Earth s Atmosphere
Earth s Atmosphere The ionosphere is ionized by high energy solar radiation. It is a good conductor. It is heated by absorbed X rays The ionosphere reflects radio waves in the AM range, but it is transparent to FM and TV The ozone layer is between the ionosphere and the mesosphere; it absorbs ultraviolet radiation which warms the mesospherestratosphere boundary
Earth s Atmosphere Convection depends on the warming of the ground by the Sun Earth s rotation causes a Coriolis force that acts on surface winds Hadley circulation arises because of different latitudinal heating and the Coriolis force
The Earth s Coriolis force also causes surface winds to rotate clockwise around high pressure and counterclockwise around low pressure in the northern hemisphere. It is the opposite in the southern hemisphere. This is baroclinic circulation. Earth s Atmosphere
Earth s Atmosphere Atmosphere scatters blue light more than red, making the sky appear blue
Earth s Atmosphere When the Sun is close to the horizon, light is scattered by dust in the air. The more dust, the more scattering; if there is enough dust, the blue light is greatly diminished, leaving a red glow in the sky.
How Planets Keep an Atmosphere Atmospheric molecules have high speeds due to thermal motion. If the average molecular speed is well below the escape velocity, few molecules will escape. Escape becomes more probable: For lighter molecules (higher speed for same kinetic energy) At higher temperatures For smaller planets (escape speed is less) Molecules in a gas have a range of speeds; the fastest (and those that are headed in the right direction) will escape
How Planets Keep an Atmosphere Loss of gases from a planet s atmosphere: Compare escape velocity (red dots) to typical velocity of gas molecules (blue lines) The planet was probably hotter in the past which would shift the red dots to the right Escape velocity less than gas molecule velocity gas escapes into space.
History of the Earth s Atmosphere First atmosphere: hydrogen (H 2 ) and helium (He); this escaped Earth s gravity Second atmosphere: from volcanic activity, mostly nitrogen (N 2 ), carbon dioxide (CO 2 ) and sulfur oxides (SO n ) Third atmosphere: Oceans dissolved all the sulfur oxides and some CO 2 which may have formed some carbonate rocks Plant life appeared, absorbing more CO 2 and creating atmospheric oxygen (O 2 ) Bones and shells of sea animals absorbed more CO 2 and their decaying bodies made sedimentary rocks and completed the absorption of CO 2 from the atmosphere Nitrogen remained from the second atmosphere
The Greenhouse Effect and Global Warming One result of modern society has been to increase CO 2 levels in the atmosphere. A corresponding increase in global average temperature has been seen as well. Exactly how much the temperature will continue to increase is not known.
Magnetic Field Lines Magnetic North Pole Magnetic South Pole Magnetic Field Lines
Earth s Magnetic Field
Magnetohydrodynamic Model of Planetary Magnetic Fields Three conditions: 1. Conducting core 2. Rapid rotation 3. Liquid core Convection
Earth s Magnetosphere The magnetosphere is a magnetic field region around the Earth where charged particles from the solar wind are trapped. The solar wind distorts the magnetosphere in a long tail that extends beyond the orbit of the Moon.
Earth s Magnetosphere Charged particles are trapped in areas called the Van Allen belts, where they spiral around the magnetic field lines.
Earth s Magnetosphere Near the poles, the Van Allen belts intersect the atmosphere. The charged particles can escape; when they do, they create glowing light called an aurora (pl. aurorae).
The Tides Caused by the Moon s differential gravitational attraction of the water on the Earth Forces are balanced at the center of the Earth Excess gravity pulls water towards the Moon on the near side Excess centrifugal force pushes water away from the Moon on the far side 2 tidal maxima 12-hour cycle
Spring and Neap Tides Spring tides The Sun also produces tidal forces, about half as strong as the Moon. Near full and new Moon, those two forces add up to cause spring tides Neap tides Near first and third quarter, the two forces work at a right angle, causing neap tides.
Tidal (differential) forces have important roles for many astronomical situations, including the rings of giant planets The Tides