So much could have gone wrong. A supernova in a neighboring star system could have blown up. Or we could have collided fatally with another planet. Somehow or other, our Earth avoided these dangers and remained life-friendly for more than three billion years. That was enough time for big life to evolve. And big life really is big. We are to bacteria what Dubai’s 830-meter-tall Burj Khalifa is to an ant crawling past the doorman’s shoes.
