Terra, commonly known as Earth, is the third planet from the Sun in our solar system. It is the only known planet to support life, featuring diverse ecosystems, including forests, oceans, and deserts. Earth has a diameter of about 12,742 kilometers and is primarily composed of rock and metal. The planet's atmosphere is made up of 78% nitrogen and 21% oxygen, which is essential for most living organisms. Earth has one natural satellite, the Moon, which influences tides and stabilizes the planet's axial tilt. The planet's surface is approximately 71% water, making it unique among the known celestial bodies.