Okay 2nd Law Thermodynamics. This one is particularly fun.
The total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value.
Not this definition of law two is taken of wikipediea (unforutnatly I don't have a physics book handy)
A key point in particular about this law states that for any isolated system the total entropy increases. (key word isolated)
By isolated meaning there are no external factors affecting the system. So for example our physical universe could be considered an isolated system in it that there is no external forces or things acting upon the universe, since the system of the universe contains everything.
Now lets take a look at an example closer to home. Lets look at the earth. If we call our system the earth all we have in this particular system would be the biospheres, the chemical reactions, the enrgy made and used on the planet.
Now we have labeled earth our system however, earth is not an isolated system because there are external factors affecting the earth that can add or remove energy from the earth. One particular example would be the sun's rays going through the earth's atmosphere and then plants using the sun's rays (electromagnetic radiation) to carry out photosynthesis, a process taking the very stable (by that meaning it takes a lot of energy to break water and carbon dioxide into its invidvudal atoms) and unreactive compounds of water and carbon dioxide and making energy bearing compounds like carbohydrates (which tend to be eaten by animals of all sorts as a soruce of energy). An example of removing energy from the system of the earth would be particles and other things that escape earth's atmosphere.
So yeah theres part of an explanation of why while 2nd law of thermodynamics is true. It does not specifically apply to the earth.
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