the deeper i drop into iron-rich hancock gorge, the further back in time i travel. okay! down here, you can look back at one of the earth's great turning points. two and a half billion years ago, the atmosphere was still without oxygen. but beneath the waves, stromatolites and their photosynthetic kin were steadily releasing this reactive waste product into the water. it didn't get far. the oceans were full of dissolved iron left over from the planet's formation.