To get a sense of how life on Earth used to be, visit Shark Bay, Australia, one of the very few places on the planet where you can see living stromatolites. These structures are rounded towers of sediment built over thousands of years by cyanobacteria, or blue-green algae. The stromatolites at Shark Bay are a few thousand years old, but they’re nearly identical to the life that thrived on Earth 3.5 billion years ago, when oxygen made up just 1 percent of the atmosphere. Though they’re found in a few extra-salty bodies of water around the world, stromatolites are at their most diverse and most abundant at Shark Bay.
