Enterobacter is a genus of common Gram-negative, facultatively anaerobic, rod-shaped, non-spore-forming bacteria of the family Enterobacteriaceae.nterobacter is a genus of common Gram-negative, facultatively anaerobic, rod-shaped, non-spore-forming bacteria of the family Enterobacteriaceae.
Trilobite fossil from the Cambrian Period. Photo Credit: Archbob. The first period in the Paleozoic Era is known as the Cambrian Period. Many of the ancestors of the species that have evolved into what we know today first came into existence during the Cambrian Explosion in the early Cambrian Period.
According to the Encyclopedia Britannica, geological eras encompass millions of years. The main eras, according to geologists, are the Paleozoic Era, the Mesozoic Era and the Cenozoic Era. The Paleozoic Era, for instance, was approximately 291 million years long, while the Mesozoic Era lasted about 185.5 million years. The Cenozoic Era has been about 65.5 million years long so far as it runs to the present day. Historical eras are defined by certain historical events or a distinctive period of time. For instance, the Elizabethan era is defined by the reign of Queen Elizabeth the First, who was the Queen of England from 1558 to 1603.