A key bed is a layer of sedimentary rock, which is usually formed in layers. These layers tell us about the earth in certain time periods. A Key Bed would be one that has very important information inside, for example.if a layer of rock had marine creature fossils in it, it tells there was an ocean at the time that this layer was at the earths crust, or surface, but just a layer above that, there could be plants and dinosaur fossils, which means the ocean disappeared and dinosaurs started to thrive. I hope this explains it well enough. Please mark brainiest, thank you :)
