26. Nearing the end of his stay in Australia, Bill drove another daunting, lonely distance to Shark Bay, on the west coast. There he was thrilled to see one of the oldest living organic forms known. What were these?
From Quiz Tidbits from "In a Sunburned Country"
Answer:
Some "living rocks".
The "rocks", called stromatolites, are actually organic formations of something called cyanobacteria (blue-green algae), which use water, carbon dioxide and sunlight to create their food, which in turn yields by-products of oxygen and calcium carbonate. They developed during a time, 3.5 to 2.7 billion years ago, when the atmosphere of the earth was rich in carbon dioxide but had very little oxygen. During the two billion years when stromatolites were the main form of life on earth, the oxygen they gave off raised the percentage of oxygen in the air until it reached about 20%, which sustains a multitude of other life forms--including, as Bill noted, himself!