Hello Earth - Origins of Our Planet - Part V
As we look at what we believe are even older planets, we see these worlds being consumed by their parent stars. As these stars die, they become hotter and larger. Just prior to the death of our Sun, it will become very large and hot. As the Sun expands outward, it will completely engulf and consume the Earth, burning it up.
Today, our planet is neither young nor old. The Earth is a middle-aged planet. It has cooled sufficiently to allow liquid water to form, but has remained warm enough to sustain life, and to keep the water from freezing.
The mountains, valleys, hills, streams, rivers, and lakes that we see today are always changing. Over millions of years, new mountains form and older mountains get worn away. Lakes form, then disappear. Streams wander through the countryside, cutting deeper and deeper into the ground creating canyons, which eventually erode away.
The Earth has many billions of years left before it will be destroyed by the aging Sun. During these billions of years it will continue to change and evolve. The Earth we know today will not be the same Earth that others know millions of years in the future. Geology is a study of how the Earth changes, while Geography is a study of the Earth as it exists today.