Various Creationists argue that the Second Law makes evolution impossible. They are usually following the argument given by Morris in "Scientific Creationism". I have a physics degree (which Dr. Morris does not), and yes, I took a course named "thermodynamics". His argument is wrong.
I don't expect you to take my word for it, of course. You can check what I'm about to say against any thermodynamics textbook, or read Abusing Science, p.89-96. Or, you can see what's said by others: the famous author Isaac Asimov: by engineering professor John Patterson: on the Web by Creationist Dr. Doug Craigen: on Usenet by NASA/JPL physicist Timothy Thompson, and by Roscoe Sincero, and by Frank Steiger, writer of several good articles and Usenet FAQs: or in the Saladin-Gish debate. For instance.
Or, alternatively, you could skip learning about thermodynamics entirely. It's pointless to have a "proof" that evolution can't happen, when evolution has been observed to happen. Whenever a child is born, and grows into an adult, every thermodynamic process that evolution demands is happening before your eyes.
For example, ask yourself: can a few cells floating around in a warm liquid turn into something complex? Before you say "No, because that's evolution", allow me to point out that it's pregnancy. And if a five pound baby can turn into a 150 pound adult, what about the 145 pounds of food that have turned into pounds of human? Clearly, material can acquire complex form. Any claim that some "law" forbids it is a false claim.
I have received some email saying that pregnancy is different because human DNA is already present. This would be a good point if the Second Law said that material cannot acquire complex form except when DNA is present. However, the Second Law has no such caveats. Material can acquire complex form, or it can't: to thermodynamics these are the only choices.
OK, you've read this far, so I owe you an explanation of the Law. It's basically a mathematical formula about work, heat, and flows of heat. It was invented to explain steam engines. The underlying assumption is that atoms and molecules bounce off each other, thus exchanging energy. The mathematics deals (statistically) with how the total energy is distributed among the molecules. And that's all. No part of it has caveats, such as "... unless DNA is present."
If we make the assumptions:
However, the Earth violates all three of these assumptions. Most importantly, we get energy from the Sun, and we get energy from radioactive material inside the Earth. These energy sources will run out someday, but until then, the Second Law is not a major problem.
For example, suppose you put some ice cubes into some warm water. Soon, you have lukewarm water, and no ice. The whole thing is at one single temperature: it's isothermal. That happened spontaneously, and it doesn't spontaneously reverse itself.
But, we can apply energy to the situation. We can, for instance, operate a stove, and make more hot water. We can operate a refrigerator, and make more ice cubes. Both of those take energy, of course. More exactly, they both waste energy. The Second Law shows that refrigerators can never be perfectly efficient. But as long as we have energy to spare, it doesn't matter much.
Imagine a DNA molecule which a living cell would consider meaningful. Now imagine a second DNA molecule, which is exactly the same, except that it has been scrambled. It's meaningless to a living cell. Do these have different thermodynamic entropy? No, they don't. To thermodynamics they are explicitly the same molecule.
When Claude Shannon invented information theory, he needed a word for one of his concepts. He chose the word entropy because he thought that there were some analogies to thermodynamic entropy. However, information entropy and thermodynamic entropy are different concepts. There are scenarios where information entropy and thermodynamic entropy both change, and in the same direction. But there are also scenarios where they both change, but in opposite directions. Clearly they cannot be measuring the same thing. Creationist Duane Gish has said otherwise:
This fundamental law of science tells us that an isolated or closed system will never increase in order and complexity -- it will never become more highly organized.Dr. Gish is misinformed. Take, for example, some salad dressing: vinegar and oil. Shake well, and little droplets of oil will be spread through the vinegar. But after a while, the droplets will merge. The oil and the vinegar will have separated. This system has gone from disorder to order, right before your eyes! There are many other examples.