what is sim earth about ? I obviously know the basics I have played sim cities . I am asking more along the lines of the details of the game. thanks
It's essentially a planet simulator. You go from birth of the planet till its "death" and have control over tweaking parameters such as mutation rates, meteor frequency, planet's axis, greenhouse effect, etc.. You may also spawn things on the planet manually, these actions normally cost energy in normal play, but there's also a mode with unlimited energy, so you can pretty much go crazy then.
The game is pretty detailed. It simulates tectonics, erosion, various natural disasters, etc. as well as evolution. Assuming you tweak your planet's temperature and weather right, you could lead to natural evolution of advanced life on your planet and eventually to civilizations being formed (although you could also just spawn a monolith on the race of your choice and have sentient fish or dinosaurs). The game doesn't keep track of any actual countries, it's just one-tile city-states, and they advance in technology and can wage war with each other (possibly even nuclear, leaving affected areas radiated). They go on doing this till they're high tech enough and decide to migrate to another planet, and the game goes on and on until your planet dies.