When you approach the Egyptian pyramids, pick up a piece of gravel from the ground, and you will see many flat and round small fossils on it, which are called currency worms. The limestone piled into the pyramid was composed of the fossils of this kind of money worm 40 to 50 million years ago. Its shape and size are a bit like coins, so it is called currency worm. In fact, its shape is more like green lentils rich in the Middle East. In front of the pyramids, there are also fossils of currency insects that have fallen from weathering. At that time, the ancient Greeks could not understand them. They thought they were air dried green lentils dropped by the ancients who built the pyramids. If you take a fossil and cut it in the middle and take it under a magnifying glass, there are hundreds of exquisite partitions in it. What is this?
It turns out that this is the shell of a foraminifera, a single celled animal, that is, the house it builds for itself. When it grows up, it adds a "room". Although foraminifera are small, they are a phylum: there are more than 3000 genera and more than 60000 kinds of fossils, and more than 6000 kinds have survived so far. Money worm is a kind of creature living on the seabed of tropical shallow sea. It can be pinched with your fingers and belongs to large foraminifera. So pyramids are really made of foraminiferal shells.
Many foraminifera live. If you travel to Okinawa, the most common souvenir is "star sand". Star sand is a big foraminifera on the local beach. Once it is caught, bleached and put into a small glass bottle, it has become a tourist commodity with high quality and low price. This kind of giant foraminifera has a "horn" on its shell, which looks like a small star. If it is cut open and viewed under a microscope, it also has a very complex internal structure.
Large foraminifera are only a small part of tens of thousands of foraminifera. Most foraminifera are not so large and can only be seen under a microscope. They are called small foraminifera. Some of them float in the upper layer of the sea and some live benthic life on the seabed. Whether large foraminifera or small foraminifera, whether planktonic or benthic foraminifera, can become fossils and be preserved in the stratum of the seabed.
Foraminifera evolved rapidly in geological periods, and there were foraminifera of different genera and species in different geological periods. When exploring oil, the key is to know the age of underground strata, while there are many foraminifera in marine strata, which can indicate the age. More than 100 years ago, Americans achieved great success in oil exploration by studying foraminifera fossils, so foraminifera suddenly became popular, and there were laboratories, publications and foundations specializing in foraminifera. Foraminifera have thus become one of the most widely used fossil families for oil exploration.