The oldest known organisms that still live on the planet are stromatolites, rock-like structures built by an algae known as cyanobacteria. Stromatolites have an extensive fossil record in Western Australia dating back some 3.5 million years, almost as ancient as the oldest rocks we know of.
The stromatolites you see in the photo are about 2,000 to 3,000 years old but they are similar to those seen in the fossil record, a living window into what the world was like so very long ago. You can find Shark Bay's stromatolites in Hamelin Pool, one of only three places on Earth where you can see living stromatolites (the other two are in the Bahamas). Hamelin Pool is a good environment for these organisms because its water is twice as salty as normal seawater, limiting predators and competition.
Shark Bay is a UNESCO World Heritage Site, in part because of its stromatolites. It's a beautiful nature preserve well worth visiting if you're in the region.