The fossil record is one of the most reliable tools in determining geological era of the earth.
Sometimes called zone fossils, indicator fossils or guide fossils, index fossils are used to guide geologists and paleontologists in the demarcation of various geological time periods. The idea is based on the fact that sediment deposits contain a record of species that lived in a particular timeframe. As sediment layers build upon each other, we can therefore understand a vast span of time in comparatively minute detail.
Argopecten gibbus
Argopecten gibbus, or the Atlantic calico scallop, is an indicator of our current geological era and period, which are the Cenozoic and Quaternary, respectively. The Atlantic calico scallop is thought to be 1.8 million years old. This bivalve is notable to the current period in that it is in danger of going extinct due to human action such as overfishing.
Viviparus glacialis
Viviparus glacialis was a freshwater snail that existed in the Pleistocene Era, 2.5 million years ago. The Pleistocene Era is best known for the fact that humans evolved into homo erectus during this period. This freshwater snail is thought to have existed for about 100,000 years before going extinct. The fossil has been discovered in sites in the UK and the Netherlands.
Paradoxides
As geological ages get more distant, the ability to narrow down a period increases from hundreds of thousands of years to tens of millions of years. The whole genus Paradoxides were trilobites that existed in the Middle Cambrian period, 540 million years ago. This era was best represented by the Gondwana super-continent landform and the beginnings of complex multicellular lifeforms.
Archeocyathids
Archeocyathids are classified as a group of sponges from the Lower Cambrian era that are the first known recorded reef-building organisms. Many organisms that are hundreds of millions of years old are found undersea in megaliths and remarkable ecosystems such as ancient reefs in the Pacific deeps.
Tags: million years, Argopecten gibbus, Atlantic calico, Atlantic calico scallop, calico scallop
