how evolution has developed from stages
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The evolutionary process has developed over millions of years. Lineages evolved and split and modifications occurred gradually in stages. Life has been in existence on Earth for at least 3.5 billion years but the first two stages of evolution took place in the space of a billion years! The earliest types of cells were believed to be 'prokaryotes', cells without a special centre or nucleus, which are free-living entities. They make proteins and reproduce without the need of a plant or animal host e.g., bacteria.
'Eukaryotes' appeared between one and two billion years ago when an oxygen-rich atmosphere was present. These were cells that contain a nucleus. Eukaryotes have their DNA structures within the nucleus which are 10 to 1000 times more than those found in prokaryotes.
Of course things have greatly speeded up since then in terms of geological time. Quite recently about 600 million years ago, there was a sudden increase in the distribution, number and variety of organisms at the beginning of what is known as the Cambrian period. Organisms with hard parts - shells, carapaces and skeletons appeared. The first fish and the first vertebrates appeared; plants, previously restricted to the oceans, began the colonization of the land; the first insect evolved, and its descendants became the pioneers in the colonization of the land by animals; winged insects arose together with the amphibians; the first trees and reptiles appeared; the dinosaurs evolved; the mammals emerged, and then the first birds; the first flowers appeared; the dinosaurs became extinct; the earliest cetaceans (ancestors to the dolphins and whales) arose and in the same period the primates (the ancestors of monkeys, apes and humans). Less than 10 million years ago, the first creatures to resemble human beings evolved, accompanied by a spectacular increase in brain size. And then just a few million years ago, the first true humans emerged.
'Eukaryotes' appeared between one and two billion years ago when an oxygen-rich atmosphere was present. These were cells that contain a nucleus. Eukaryotes have their DNA structures within the nucleus which are 10 to 1000 times more than those found in prokaryotes.
Of course things have greatly speeded up since then in terms of geological time. Quite recently about 600 million years ago, there was a sudden increase in the distribution, number and variety of organisms at the beginning of what is known as the Cambrian period. Organisms with hard parts - shells, carapaces and skeletons appeared. The first fish and the first vertebrates appeared; plants, previously restricted to the oceans, began the colonization of the land; the first insect evolved, and its descendants became the pioneers in the colonization of the land by animals; winged insects arose together with the amphibians; the first trees and reptiles appeared; the dinosaurs evolved; the mammals emerged, and then the first birds; the first flowers appeared; the dinosaurs became extinct; the earliest cetaceans (ancestors to the dolphins and whales) arose and in the same period the primates (the ancestors of monkeys, apes and humans). Less than 10 million years ago, the first creatures to resemble human beings evolved, accompanied by a spectacular increase in brain size. And then just a few million years ago, the first true humans emerged.
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