The hydrologic cycle works like a huge water pump powered by solar energy and gravity. It is a global system, and every molecule of water on Earth travels through it. Because it is a cycle, it has no beginning or end. For three and a half billion years, the Earth’s water has been moving from streams to lakes to oceans, flowing underground, sitting high up on mountain glaciers, freezing and melting on the edges of the polar ice caps and forming clouds in the atmosphere. Average weather conditions over time is what we call climate. Texas is so large it is affected by air drawn in from the Pacific Ocean as well as the humid topical air flowing in from the Gulf of Mexico.