Claiming there is no other life in the universe is like scooping up some water, looking at the cup and claiming there are no whales in the ocean.
He invited people to sign a petition that demanded either strict control of, or a total ban on, dihydrogen monoxide.... Yes, 86 percent of the passersby voted to ban water (H2O) from the environment. Maybe that's what really happened to all the water on Mars.
Where there's water on Earth, you find life as we know it. So if you find water somewhere else, it becomes a remarkable draw to look closer to see if life of any kind is there, even if it's bacterial, which would be extraordinary for the field of biology.
Seventy percent of Earth's surface is water and over 99 percent is uninhabited, so you would expect nearly all impactors to hit either the ocean or desolate regions on Earth's surface. So why do movie meteors have such good aim?
Some molecules - ammonia, carbon dioxide, water - show up everywhere in the universe, whether life is present or not. But others pop up especially in the presence of life itself. Among the biomarkers in Earth's atmosphere are ozone-destroying chlorofluorocarbons from aerosol sprays, vapor from mineral solvents, escaped coolants from refrigerators and air conditioners, and smog from the burning of fossil fuels. No other way to read that list: sure signs of the absence of intelligence.
