The law of entropy only applies to a closed system, which the Earth is not. We have energy input from the sun, which powers photosynthesis in plants, allowing them to build and store nutrients that humans consume, fueling our engineering endeavors. So a decrease in usable energy in the sun turns into an increase in usable energy here (in the plants), and ultimately, humans do use this energy.
As far as the bigger picture is concerned, though, the existence of life at all would violate thermodynamics for two reasons if atheism were true. First, it would mean the universe is a closed system, and the universe is supposed to have started as hot plasma - one of the most chaotic systems known. Fast forward several billion years, and we now have incredible structures like the human brain, which Isaac Asimov called "the most complex and orderly arrangement of matter in the universe." With no input from an agent outside the universe, the increase in order would certainly be a violation of the second law.
And second, order doesn't just increase with an addition of energy. The addition itself must be orderly. If you add chaotic energy, you actually increase the chaos of the system. A good example is a puzzle. Suppose you open a puzzle box and empty its pieces on to a table. The puzzle begins in a state of chaos; the goal of the puzzle is to put its pieces into a state of order. That cannot be done by adding random energy. If you sat some monkeys down at the table, they'd start throwing the pieces around - energy is being expended, but the order not increasing. You must apply orderly energy to increase a system's order. So the origin of DNA, cells, and complex life in the first place could not be achieved just be giving the Earth energy from the sun or other random sources like lightning strikes.
