These patterns are stromatolites. They can be flat layers, they can be puffy mushroomoids, they can be made of white limestone or they can be made from iron. And they can be clues about life on other planets.
Stromatolites are the oldest fossils in existence. They'd have to be, since they're remnants of the oldest lifeforms in existence. Bacteria have been living on planet Earth for about three and a half billion years; they have a lot of history, but don't have any bones, which makes them tough to fossilize. The stromatolites are leftovers of what are called microbial mats. If you've ever walked along a beach, or a lakeshore, or a marsh, and seen disgusting, slimy, discolored patches of ground, you've probably seen one. They're bacteria colonies.
As the bacteria colonies grow, they do one of many things. Some disrupt the chemistry of sea water, making calcium carbonate precipitate down over the colony. Some produce oxygen, which reacts with iron to form iron oxide, which also joins the sediment. Any number of chemistry experiments can lead to different compositions of sediment. The bacteria grow through the layer of sediment, only to crank up their internal chemistry and make more. As they grow — upwards and outwards — they leave more and more layers. Biologists find these layered fossils billions of years later.
Because these deposits can happen in almost any environment, and because they represent the most basic and ubiquitous life in the world, they let scientists know what kind of markers of life to look for on other planets. Perhaps one day we'll find deposits just like these elsewhere in the solar system, and know we're on to something.