Goals Compare the Earth and the Moon and explain differences Describe the effects of gravity between the Earth and Moon Explain the greenhouse effect Discuss theories of formation and evolution of Earth and Moon

Mass=1.0 Density=5500 kg/m3 Gravity=1.0 Escape Velocity=11.2 km/s Rotation period=23h 56m Mass=0.012 Density=3300 kg/m3 Gravity=0.17 Escape Velocity=2.4 km/s Rotation period=27.3 days

Tides The gravitation attraction between the Earth and the Moon causes a tidal force resulting in deformations of the solid surfaces of both and the oceans of the Earth. Since the oceans are liquid they can respond more. As the Earth rotates under the tidal bulge the surface experiences two high and low tides each day. Since the Moon does not rotate under its bulge (synchronous orbit), it does not experience tides.

The Sun produces about half as much tidal force on the Earth as does the Moon. When they are aligned (New and Full Moon) the effects add. (spring tides) When they are perpendicular to each other (1st and 3rd quarters) their effects tend to cancel. (neap tides) What time of the month should we go to the beach? Because it takes energy to make tides, the two bodies tend to lock their rotation and revolution rates.

Tides are most pronounced when you are up close to a large (strong gravity) object (like a black hole). Therefore the tides the Earth imposes on the Moon are stronger than the tides the Moon imposes on the Earth Because of this the Moon has been locked in its rotation long before the Earth will. Earth’s day used to be 21 hours long and the year was 410 days. The ultimate outcome of the tides is that the Earth and Moon will both be locked and one rotation of the Earth will take 47 days and the Moon will be 550,000 miles distant.

Earth’s Atmosphere Several different layers are defined in the atmosphere. The heating of the ground by the Sun causes convection cells which (a long with rotation) ultimately produce Earth’s weather patterns.

The Earth has been blessed with a substantial atmosphere Nitrogen 78 % Oxygen 21 % Argon 0.9 % Carbon Dioxide 0.03 % Water Vapor 0.1-3 % The Moon has none and was permanently polluted by the visit of the Apollo astronauts. The reason is that the Earth’s temperature and gravity are such that these molecules have average velocities less than the escape velocity of the Earth, while the Moon’s low gravity and high temperatures prevent it from holding onto these gases. Escape velocity a sqrt(mass of planet/radius of planet) molecular speed a sqrt(temperature/mass of gas)

While the ozone layer does not effect Earth’s climate, it does block harmful UV rays from reaching the surface. Scientists discovered CFC were depleting the ozone. New formulations of Freon no longer deplete ozone but they don’t work as well either.

The greenhouse effect does not involve Ozone but CO2 and H2O. The sun’s radiation makes it through the atmosphere and warms the ground. While the Sun’s blackbody curve peaks in the visible (5000ko), the Earth’s blackbody curve peaks in the infrared (300k0) where the gases are not transparent. Thus these gases hold in the heat from the earth. Without these gases the Earth would be 40o cooler.

Many climatologists believe that mankind is responsible for increasing the CO2 levels causing global warming.

Earthquakes help us deduce that Earth’s core has a liquid component because only compression waves make it through. We lack corresponding data for the Moon.

Because Earth has a liquid core undergoing convection, its surface is dominated by “plates” that float on the convection cells. The collision and separation of these plates (plate tectonics) causes Earthquakes, volcanoes, mountain ranges, and ocean trenches. The drift of the continents was first detected by radio interferometers.

The plate boundaries are where most quakes and volcanoes exist.

While the continents were once a solid mass, tectonics has caused them to split and migrate away giving the current positions of the continents.

The Moon’s surface contains craters, mountains, and evidence of lava flow. Due to its airless environment and lack of geologic activity the surface of the Moon has remained largely unchanged for billion of years. There are two distinct regions: the highlands (terrae), lowlands (maria).

Near side of Moon Far side of Moon

Sizes from 50 km to 500m

The Moon’s surface has been bombarded by meteors. This has caused craters of all sizes. Most of the bombardment occurred billions of years ago during the formation of the solar system. Because of this the Moon’s surface is covered with dust 20m thick. The highlands are much more heavenly cratered proving they are older. The lowlands are the result of lava flooded plains

Another feature that makes life possible on Earth is its magnetic field. It deflects the charged particles from the Sun (solar wind).

The charged particles follow the magnetic field lines until they become so strong near the poles were they are reflected. This back and forth travel produces the Van Allen radiation belts.

During exceptionally strong Solar storms, the charged particles make down through the atmosphere before being reflected back. These charged particles then excite the Nitrogen and Oxygen atoms in the atmosphere and cause them to fluoresce. We call these the Aurora (northern lights).

It is now believed that the Moon was created during a collision of the Earth with a Mars sized object. The simulations show the heavier (iron) material fell into the center of the Earth while the lighter outer rocks formed the Moon. This explains some of the similarities and differences between the Earth and Moon.