Page 21 - The Dinosaur Book and Other Wonders of the Prehistoric World (DK-Smithsonian)
P. 21
When cyanobacteria evolved in the oceans more than existence to these microbes. Free-living cyanobacteria
2.5 billion years ago, there was very little oxygen in the air. are still widespread in oceans and on land, but thriving
Over millions of years, they pumped out so much that it now stromatolites are rare because they were ideal food for some
makes up more than a fifth of the atmosphere. This was vital of the animals that evolved in the world they had created.
for the evolution of animals, which need oxygen to turn food The ones in Shark Bay survive because few animals can live
into energy. So all the animals that have ever lived owe their in the very salty water of its lagoons.
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