The earth's axis of rotation is tilted relative to the earth's path around the sun. As a result we are tilted towards the sun in the summer and away from the sun in the winter.
The link sends you to a good over-all article to start with.
1000
4000000000 degrees
The very center. he belived everything revolved around the earth.
Relative to what. It has an mean density of 3.3464 g/cc.
According to the Washington Post's article on the "middle eastern kelp phenomena of 2012" this week, "Kelp covers approximately 94% of the earths surface."
Not only the earth's rotation , the lunar phases change cyclically as the Moon orbits the Earth, according to the changing positions of the Moon and Sun relative to the Earth.
Years are defined as the amount of time it takes to go all the way around our sun.
superposition a&c- Jackie
it is determined by studying the relative and absolute ages of rocks and fossils
The earth's atmosphere can be imagined as the same relative thickness as the varnish on a model globe.
The earths orbit around the sun is almost circular.