Each year, the foul machine we call civilization spews millions of tons of pollution, toxins, and radioactive waste into our rivers, oceans, and atmosphere. And global warming threatens to grill us like steaks on a barbecue. A nuclear war could end all life in hours. In the unlikely event that we wriggle our way out of our present predicament and avoid the minefield of potential calamities, nature holds in store for us a disaster of such magnitude that not even dumb luck can save us. In a few billion years our sun will run out of fuel and expand into a giant red star that engulfs the Earth and even Mars, killing all life in our solar system.
Earth is a dangerous place, indeed.
So dangerous, in fact, that if we choose to stay here, we will all die. And so will every other form of life on Earth. Our universe is a very large place and may very well be crawling with life. Our universe is about 15 billion years old, and nearly 12 billion of those years passed before life sprang up on Earth. Another 3.8 billion years passed before the first sentient being arrived.