The size and age of the Cosmos are beyond ordinary human understanding. Lost somewhere between immensity and eternity is our tiny planetary home. We explore a little but have not even scratched the surface. The unit of measure of which we measure distances for space is the light year. There must be life on other planets. How could one star (the sun) be the only star to be accompanied by an inhabited planet? Our destiny is to explore the Cosmos.
The study of the circumference of the earth began around the third century B.C. by a fellow named Eratosthenes. He used sticks, shadows, and reflections in wells, taking advantage of the sun at different locations such as, Alexandria and Syene. Eratosthenes" calculations about the earth being round sparked many explorations by sea. Now that Earth is thoroughly explored, it permits us to venture into space and explore new worlds.
Cosmos is a Greek word for the order of the universe. It is, in a way, the opposite of chaos. We now know the cosmos is very old. We know our universe is some fifteen or twenty billion years old. We have examined the universe in space and seen that we live on a mote of dust circling a star in the corner of an obscure galaxy.
I believe that there is definitely life on other planets. Earth couldn't possibly be the only planet with life on it. Carl Sagan really gets you to think about these kinds of things in his book and on his thirteen episode series. I enjoy reading and watching his work in the Cosmos and can't wait to get to the next chapter.