Decades ago, the Morning Glory pool at Yellowstone National Park was a gorgeous deep blue. But because tourists have thrown coins, rocks, and trash into it for years, the spring has now turned into a sickly yellowish green. Now, a new optics study is shedding light on the pool's unfortunate change of color.
As recently as 600 million years ago, oxygen levels were extremely low on Earth, only about a tenth of what they are today. So how did ancient animals move around and avoid mass asphyxiation?