Index fossils delineate the epochs of geologic time. In
order for an organism to be considered as an index fossil it must possess at
least one of the four characteristics: it must be unique, extensive, abundant
and inadequate in geologic time. Most type of organism may be considered
distinctive but not widespread which tolerate them to inhabit all over the
world. While some are considered abundant that they were able to be developed as
the most susceptible to environmental modification and destruction. Just like
the trilobites, this is known as a precise example of index fossil for the
Paleozoic rocks that is inhabit in all parts of the ocean. They develop new
species throughout their being, which is according to some reports, lasted 270
million years from Middle Cambrian time to the termination of the Permian
Period. Because of their ability to travel, they tend to dwell in global areas.
The trilobites are huge that they can be used in a study even without a
microscope and they are also hard-shelled invertebrates which make them petrified
effortlessly.
