Cosmic Perspectives from Amid the Stars:
Astronomy Blog

Earth is the only planet we know in the entire universe to support life. In a universe as big as ours, life likely exists out there somewhere by sheer odds alone. But for now, Earth is all we know and the only example of a habitable planet we can study. So why can Earth support life when so many other planets fail? In order to predict what other planets might support life, we first need to understand life on Earth. What is it that makes Earth perfect for life?

According to our best estimates, the universe is 13.8 billion years old. It goes without saying that that’s extremely old. But just how long of a time is 14 billion years? The human mind has a way of underestimating massive numbers. So, to truly understand the implications of a nearly 14-billion-year-old universe, we need a scale model. Famous astronomer and science communicator Carl Sagan introduced the concept of the cosmic calendar for exactly this reason.