I was on a ten-day tour of Western Australia, and one of the stops was at a place called the Stromatolites. I had never heard of them, but our guide Jared said that none of us would be alive if it weren't for them. I was intrigued, and so I listened to his explanation.

Stromatolites are rocks that were formed by the growth of cyanobacteria, which are bacteria that turn light into oxygen. Stromatolites have existed for over 3 billion years, whereas plants have only existed for about 470 million years. That's a very small part of Earth's 4.5 billion year history!

In fact, there is a theory that the Great Oxygenation Event, whereby the amount of oxygen in the atmosphere greatly increased between 2.4 and 2 billion years ago, was triggered at least partially by cyanobacteria. That means that without stromatolites and cyanobacteria, the atmosphere may never have had enough oxygen for animals and eventually humans.

Today, most of the stromatolites that exist are found in bodies of water that contain extreme amounts of salt, like the Hamelin Pool Marine Nature Reserve in Western Australia. Our guide told us that he sometimes gets biologists who traveled all the way to Australia to see the stromatolites. So we were lucky to get to go to such a unique place without even planning to do so!

Sample Problems

1. Create a timeline spanning the last 4.5 billion years, starting with Earth's formation and including the events listed on this page.

2. Conduct further research on important dates in the evolution of life on Earth, such as the earliest life, the first dinosaurs, and the first humans. Include these on your timeline.

3. Read more about the Great Oxygenation Event, which is a topic that is not always covered in standard high school biology courses but nevertheless a fascinating and important event.