The Earth is in continual development.
The history of the Earth tells the story of one planet. Its development sits within the story of the universe, much of which is unknown. The phases of Earth's development have been studied and reconstructed through the lenses of multiple natural sciences from geography to paleontology via geology. The Earth is approximately a third of the age of the universe and spent much of its existence coming into shape and being. These developmental phases, or stages, are divided into those that brought the planet into its physical shape and place, and those that saw its atmosphere and landscape develop. It is a history that covers 4.6 billion years.
Hadean
The Hadean phase, named after the Greek underworld (Hades), is the Earth's only non-geological era. This means there were no rocks on the Earth with the possible exception of meteorites. The Hadean phase covers the early development of the solar system when a large gaseous disc gathered around the sun. These gasses and other materials slowly gathered into the sun and the planets we know today. The various impacts of gravitational centers such as the Earth released a lot of heat and kept the Earth molten for a long time.
Archean
The Hadean era ended as the Earth's outer reaches began to cool and produce what we live on today, the Earth's crust. Thus, the Archean period began. The name comes from the ancient Greek word for origin. The planet's early atmosphere was completely different from today's. The early atmosphere consisted mostly of methane, ammonia and other toxic gases. During the Archean era the early continental plates formed. Geologists have dated the earliest rocks to around 3.9 billion years ago, and paleontologists date the first fossils to 3.5 billion years. These early fossils show the first rumblings of life and came in the form of bacteria.
Proterozoic
The Proterozoic Era saw the relative stabilization of continental plates and a flourishing of life. It covers the Earth's development from 2.5 billion years ago to around 543 million years ago. Bacteria were joined by eukaryotic cells during this time. Eukaryotic cells are the basic precursors of all animals, plants, fungi and protozoa. Their modern descendents share similar cell organization, biochemistry and molecular biology. During the middle of the period oxygen began to build up in the atmosphere. As a result many bacteria families were killed off, but eukaryotic groups were able to flourish and develop into the first animals.
Paleozoic
The Paleozoic Era lasted from 543 to 245 million years ago and is subdivided into the Cambrian, Ordovician, Silurian, Devonian and Carboniferous periods. These periods saw an explosion in animal life and included the first cases of animals moving onto land. It was also the time of the super continent called Pangea. Life proved fragile as various Earth events from changes in temperature and atmosphere to volcanic eruptions caused mass flowerings of life as well as mass extinctions. As the era wore on the climate began to stabilize during the Silurian period, and creatures such as centipedes, jawed fishes and vascular plants evolved.
Mesozoic
The Mesozoic can also be called the "Age of the Dinosaurs." The period is divided into three periods: the Triassic, the Jurassic and the Cretaceous. The era runs from approximately 245 million years ago to 65 million years ago. The period saw vast changes in life forms across the world and included some of the most famous beasts of yesteryear from the Tyrannosaurus rex to the stegosaurus to the archaeopteryx. The era was also extremely warm, and the Earth had no ice caps.
Cenozoic
The Cenozoic era is also the modern era and dates from 65 million years ago to the present day. Dinosaurs died out in the Cretaceous period, leading to the dominance of mammals in the world. The Cenozoic is also an era of flowering plants, insects and birds. During this era plate tectonics moved the continents into their modern form. Climatically the Earth saw a period of rapid cooling and a number of ice ages.
Tags: million years, billion years, Cenozoic also, continental plates, divided into, early atmosphere, Earth development
