Stromatolites form when carpets of microbial life (usually cyanobacteria) are covered with a layer of sediment. That layer is then repeatedly covered by more cyanobacteria, which is covered by more sediment, and so on and so forth. When this structure fossilizes, we can see the layers formed in stone. Stromatolites can have different colors due to the type of minerals that made up the sediment. Sometimes Stromatolites are cut into slices so that those layers are visible, as pictured here.
Stromatolites have been forming for as long as cyanobacteria have existed, which is a really long time (about 3.5 billion years ago), and continue to do so in certain marine environments today.
Behold: the oldest animal ever (on record, at least)! The Dickinsonia may not look like much, but this little dollop of creature represents one of the first true animals to ever live on planet earth. The Dickinsonia lived before there was any need for defensive adaptations because it had no predators, resulting in this slow-moving, soft body plan. They ranged in size between a few millimeters to 4.5 feet in length, and it is believed that they lived a peaceful life creeping over the ocean floor and fed on algae and bacteria.
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