Diatoms are single-celled algae, found in the oceans, waterways and soils of the world.. They have a shell made of glass that gets left behind after they die. These shells then form chalky rocks like the ones in the image. They were first seen during the Cretaceous time period and are still alive today. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion metric tons of silicon each year from the waters in which they live, and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was formed a few thousand years ago when Lake Chad was draining.

Thrombolites are like stromatolites, but they form clot-like, not linear structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria. They probably evolved from stromatolites. They also provided shelter for the first multicellular organisms. They are now only found in a few places in the world. The ancestors of thrombolites and stromatolites are thought to have contributed to the increase in oxygen in Earth's atmosphere.

Stromatolites look like rocks but they are actually communities of photosynthesizing microbes covered by a layer of calcium carbonate. They were the first visible signs of life and first appeared 3.5 billion years ago. Fossilized stromatolites provide records of ancient life on Earth. They produced oxygen, which allowed more types of living things to form.

Radiolarians are single-celled zooplankton that ate diatoms. They were first found over 541 million years ago. The elaborate mineral skeleton is usually made of silica.[1] They are found as zooplankton throughout the ocean, and their skeletal remains make up a large part of the cover of the ocean floor as siliceous ooze. Chert, the rock their shells form, make up much of the ocean floor. Due to their rapid change as species, they represent an important diagnostic fossil found from the Cambrian onwards.

Foraminifers are single-celled protozoa that have a calcium carbonate shell called a “test” that comes in different shapes and sizes. Most foraminifers are marine, the majority of which live on or within the seafloor sediment , while a smaller number float in the water column at various depths They were first found in the Cambrian Time Period 541 million years ago. You can find foraminifer fossils in the rocks used to build the Pyramids of Giza.