During the first period of its history the Earth, like all the other planets of the Solar System, has been subjected to an intense bombardment of the material that went through gravity to form protoplanets. It was during this period, about 4.5 billion years ago that formed the Moon, probably due to a collision between early Earth and a Mars-sized body on the planet.
On the Moon, Mercury, Mars, and many small bodies in the solar system is almost nothing in their heavily cratered surfaces of this period, which ended about 3.8 billion years ago. The surfaces of these bodies have little altered since then, due to the lack of atmosphere and the lack of endogenous activity. Venus and the Earth, by contrast, have been completely transformed by geological events: for Venus volcanism and plate tectonics and erosion by water and weather events on Earth.
Makes approximately 3500 million years ago began to develop life on Earth in the form of single-celled Organisms known as Prokaryotes, from Organic Molecules formed by synthesis in the waters. A few 1400 million years began to develop Chlorophyll Bacteria (Cyanobacteria), which photosynthesis could produce their own food.
A few 800 million years and were very primitive Multicellular Organisms. About 600 million years ago the first Multicellular animals appeared similar Jellyfish and Worms. Chordate animals, or with dorsal cord, the group we belong, appeared about 550 million years.
450 million years ago appeared the first land plants, because until now there was only life in the water, and began to populate the continent. 370 million years ago came the first land animals as Spiders, Scorpions and Insects. Begin to develop large animals that feed on Plants and Insects. Fish dominated the seas.
300 million years ago came the Amphibians (frogs and toads), who developed the quality of laying eggs, but always in the water. 270 million years ago and there were reptiles from Amphibians, which began to populate the seas and continents of them began to develop the first Birds, which had feathers instead of scales.
220 million years ago Mammals appeared, with Teeth and Hair, and laid eggs or gave birth to undeveloped embryos. About 100 million years placental Mammals appeared, which developed for farming in the body and in a special envelope, called placenta. Some 70 million years developed a special group of mammals known as primates or Monkeys, which is the group to which humans belong.
The Monkeys continued to evolve into new forms and finally 4 million years ago led to a company that is already very similar to modern Humans. The development center was in Central-Africa and the continent, it seems, has been the cradle of humanity.
Since its formation to the present, the Earth has undergone many changes. The first stage from the start of the solidification of the mass glow until the appearance of a permanent cortex, left no evidence of their passing, as the rocks that were generating, turned to melt or simply were swallowed by an eruption. These early stages are still a mystery to Science. Furthermore, Over time, Erosion, Various changes, signals have been blurred, so that the more ancient the period to be analyzed, the more difficulties we will encounter. Earth, lest we forget, is still evolving and changing.