Archeozoic Era (4500-1500 million years ago)
This is the first Era to have geologic record. In this early stage of the earth, the surface changes from molten to rock. The continental plates also formed during this timeline. The atmosphere of the earth is made up of 75% nitrogen & 15% carbon Dioxide. These are known as prokaryotic cells. They have free-floating DNA, have no nucleus, and lack membrane-bound organelles associated with higher forms of life. Also
Proterozoic Era (2500 to 542 million years ago)
In this Era, there are cells with a nucleus and organelles. The important function of these organelles is that they perform special functions that are needed for the evolution of fungi, protists, plants, and animals. Nearing the end of this Era soft body organisms appeared such as jellyfish.
Paleozoic Era (542 to 151 million years ago)
This is the era in which much change had occurred. The first hard parts species started to appear such as primitive fish, coral, plant life, Vertebrate animals form along with arachnids, and wingless insects. During the end of the Paleozoic Era, the Permian Period begins. There was a great extinction that wiped out roughly 95% of all life forms on the planet during that time. There has been no conclusion on what may have caused this, but there is evidence that when many continents formed into one massive continent (called Pangaea) it may have caused the earth to be unstable and mass volcanos appeared which destroyed the oxygen level balance.
Mesozoic Era (251 to 65.5 million years ago)
This is the dinosaur age. The Mesozoic is broken up into three periods. The Triassic, the Jurassic, and the Cretaceous Period. In the Triassic period, there were many primitive dinosaurs forming as well as many species of marine reptiles. Some of the first species of dinosaurs were the Plateosaurus, Eoraptor, Herrerasaurus, Pisanosaurus, Saturnalia, Staurikosaurus. In the Jurassic Period dinosaurs such as Diplodocus and Apatosaurus, and carnivores such as Allosaurus flourish the earth. The first reptiles with primitive abilities to attempt flight appeared such as Archaeopteryx as well. The dinosaurs of this time period began to evolve much larger in size and many ocean-dwelling reptiles were becoming extinct. In this Period the evolution of Sauropods(Long-necked dinosaurs) was at its peak. During the Cretaceous Period, the Ceratopsidae family begin to form which includes many plated dinosaurs with defense body features such as spikes such as the Triceratops. At the end of this Period and Era, there is a large dinosaur extinction that completely wiped out all dinosaurs living on the earth. Although not proven there are several theories on why this has happened.
Cenozoic Era (65.5 million years ago to today)
The oldest known modern mammals diversify and radiate across the continents. The appearance of the first elephants, horses, and other hove mammals existed in this Era.