Geological evidence suggests that the earth is about 4.6 billion years old. The principal evidence comes from the use of radioactive dating. 

Atmosphere

Nitrogen: 78%; Oxygen 21%.

Pressure: Near sea level about 10⁴ Kg/m²  (about 15 pounds per square inch).

Thickness: Above 8km the air is too thin to breath.

Origins

Originally it was thought that Earth's atmosphere must have been similar in composition to the solar nebula. However, studies indicate that the planets were very hot when they formed. Consequently, gases like nitrogen, carbon dioxide and water vapor would have been released from the rock that formed the Earth. Therefore, the Earth's primeval atmosphere must have been rich in these gases. 

The water vapor in the atmosphere eventually rained down to form the oceans, when the Earth was cool enough to support liquid water. 

Carbon dioxide, which is highly soluble in water, was drawn into the oceans. The ensuing chemical reactions with other compounds in the oceans transformed the carbon dioxide into mineral compounds like limestone and silicon dioxide (sand).

Thus the oceans were very effective at reducing the level of carbon dioxide in the atmosphere and leaving it nitrogen rich. 

Ozone Layer

One critical development in the atmosphere was the generation of a layer of free oxygen O₃, called the ozone layer, which lies between 15 and 30 km. This layer absorbs ultraviolet radiation--a critical function for life on the planet. Early on the atmosphere had no free oxygen. It was only after life developed photosynthesis, about 3.3 billion years ago, that oxygen began to appear in abundance in the atmosphere.

Plants absorb carbon dioxide and generate free oxygen. Meanwhile oxygen, because being highly reactive, is depleted from the atmosphere. A balance has now been achieved. But it is one that could be upset if the rate of oxygen depletion fell below that of carbon dioxide removal.

The Greenhouse Effect

When sunlight falls on an object  the latter heats up and radiates some of the energy as infrared radiation. Unlike sunlight, infrared radiation cannot pass easily through glass. This is how a greenhouse works: the sunlight enters the greenhouse, but the heat rays (infrared radiation) cannot leave, thereby, increasing the temperature within the greenhouse. 

The same sort of thing happens in the atmosphere: sunlight strikes the Earth and heats it. This in turn causes the Earth to radiate some of the energy in the infrared. But carbon dioxide is opaque to infrared. Therefore, the carbon dioxide in the atmosphere tends to trap the heat. 

The greater the concentration of carbon dioxide the greater the tendency to trap heat. 

Venus, with its dense atmosphere of carbon dioxide, provides an example of the catastrophic effects of too much carbon dioxide: an extreme greenhouse atmosphere. 

Tides

Caused by the gravitational interaction between the Sun and the Earth and the Moon and the Earth.

Think of the oceans as a fluid shell that is fixed, approximately, relative to the Moon and the Sun while the solid Earth spins on its axis within this fluid shell.

The gravitational forces of the Sun and the Moon distort the oceans from a spherical shell to a shape resembling an American football: The oceans are raised in two regions, like the pointed ends of the football, and depressed in the regions that are at right angles. 

As the Earth turns through the fluid shell, that is the oceans, the depth of water at each point on the Earth's surface increases to a maximum then decreases to a minimum. This happens twice per day because there are two raised regions of water.

The distortion of the oceans is most pronounced when the Sun, Earth and Moon are lined up (the Spring Tides) and least when the Sun, Earth and Moon form a right angle with the Earth at the vertex of the angle (the Neap Tides).

Because the solid Earth moves through the oceans there is a frictional force between the oceans and the Earth. This frictional force causes the Earth's spin to slow down--an effect called tidal breaking. The day is getting longer each century by about 2 milliseconds!
 

A spectacular place to see the power of tides is Le Mont Saint Michel in Normandy, France. The region around Le Mont Saint Michel is extremely flat, so the sea comes in very fast--as fast a galloping horse it is said!

Coriolis Effect

Gustave Gaspard Coriolis (1792-1843) was born in Paris and became the director of the prestigious Ecole Polytechnique. 

He was the first to study in detail the effect of planetary rotation on the movement of objects. The coriolis effect influences the movement of the atmosphere on rotating planets. The spiral pattern observed in large storms on Earth is caused by the coriolis effect.

Turmoil in Coriolis' Europe

The young Coriolis lived during a time of great unrest in Europe. Here is a sketch of the main events.

The MOON

Full Moon

Apollo 11

Lunar Rover

Structure

Distance from Earth--380,000 km

Topography

It is thought that most of the lunar surface features, including the surface layer of powdered rock (called the regolith--``blanket of rock"), were created by the high velocity impacts of solid objects with the Moon. 

The absence of significant seismic activity within the Moon suggests that its interior generates very little heat compared with that produced at the Earth's core. The Moon's crust, unlike the Earth's, is un-fractured. 

The Moon has a lower average density than the Earth, which suggests that the Moon's core contains a smaller concentration of iron than does the Earth's.

It is interesting that the lunar rocks brought back to Earth by the Apollo astronauts have a similar composition to those of the Earth's crust. One  hypothesis to explain this is that the Moon was formed from the outer layers of the Earth.

The Moon has no atmosphere because its gravitational force field is too weak to retain one. Any atmosphere that might have existed has long since escaped into space.