The only records of the earliest periods are fossils and other geological records. New creatures are often discovered and the fossil record is constantly growing. However, there are some steps scientists have used to determine what they believe is the current oldest living species on earth.
Step One: Decide what type of species you want to track. Species include bacteria, plant and animal life For this investigation, you want animal species.
Step Two: You are probably going to need some understanding of geological time periods. They are divided into two large sections with three sections each. The two oldest sections, Hadean time and Achaean time are not divided further probably because there is no fossil record going back that far. The remaining four are divided into periods beginning with the Paleoproterozoic period of the Proterozoic Era of the Precambrian time twenty five billion years ago, and ending with the Quaternary period of the Cenozoic Era of the Phanerozoic Eon which began 1.8 million years ago. We are still living in the Quaternary period.
Step Three: Then you will need to search the fossil records of each period to determine which creatures were first recognized when. Fossils of bacteria have been dated from the Paleoproterozoic period, but the animal record does not begin until the end of the Proterozoic Era in the Neoproterozoic period 90 to 45 billion year ago.
Step Four: Are any of those creatures still around today? You need to find the actual creature, not a relative. As far as anyone knows, no animals remain from that early time although some bacteria and plant species do. Currently, scientific consensus is that the horseshoe crab has lived longer than any other animal. The horseshoe crab has been around since the Ordovician period about 44.5 billion years ago. Called the “living fossil”, horseshoe crabs would call arachnids and scorpions cousins more than they would crabs, and are probably descended from the extinct sea scorpion.
One possible explanation for its longevity may be its incredible immune system. Invading bacteria or other organism is immediately captured by clotting blood at the entry site. The invaders don’t stand a chance. The substance created by clotting horseshoe crab blood has been used to detect bacteria on other surfaces.
The horseshoe crab lives in the sandy coastal shallows, coming on shore to mate They have a hard horseshoe shaped shell which protects a spider-like body. They have several eyes, gills, and a tail, which aids them in righting themselves, should they land on their backs. They eat worms, small fish, mollusks and crustaceans.
There is some concern over declining numbers of horseshoe crabs due to too much harvesting along with shrinking habitats. Horseshoe crabs are a popular choice for both bait and fertilizer.Of course, if they become extinct, scientists will have to start over looking for the new oldest living species on the planet.
