Major evolutionary innovations in the first three billion years of life on Earth were the evolution of oxyphotosynthetic bacteria and complex cells. The evolution of a third germ layer, predation, eyes, colonization of the earth by plants and animals, and true flight are the most important evolutionary innovations. The transfer to land is more important than the transition to air, occurring between 460 and 430 million years ago. Flight evolved independently four times.
Evolutionary breakthroughs appear to have been relatively few and far between in the first three billion years or so of life on Earth. The major evolutionary innovations during this period were the evolution of oxyphotosynthetic bacteria and complex cells (eukaryotes). Although life itself originated at least 3.7 billion years ago, it was only about 600 million years ago that the first solid evidence of multicellular life appeared.
Aside from the evolutionary innovations of the (unicellular) protozoa, which many scientists argue are the most important of all for technical reasons, there are a number of evolutionary innovations, the utility of which is obvious to anyone. Five evolutionary innovations that seem most important are the evolution of a third germ layer, which allows for a body cavity, also called a coelom; predation, which has ignited an arms race for evolutionary change; eyes, which after their initial evolution have been so successful that most macroscopic animals have them; the colonization of the earth by plants and animals; and the evolution of true flight, which occurred independently four times and opened up a huge new niche for animals to colonize.
The evolution of a third germ layer, i.e. triploblastic animals, occurred between 600 and 580 million years ago. The earliest known triploblastic fossil is Vernanimalcula guizhouena, a tiny spherical animal just 0.1 mm in diameter. This animal has been found to have two body cavities that separate its intestines from the body wall. This physiological arrangement helps cushion the internal organs while decouples the structural dependencies between the two, allowing them to develop independently. This is an invaluable evolutionary innovation.
The evolution of predation and eyes probably occurred very early together. Given what we know, it’s reasonable to assume that both of these events occurred around the same time, at the Cambrian-Precambrian boundary about 542 million years ago. All animals with eyes are monophyletic, meaning they share a common ancestor that evolved during this time. This is in contrast to an earlier view which stated that the eyes evolved independently on different occasions. During the same period, the first organisms with hard shells appeared, and small holes can be seen on these shells – a telltale sign of predators. Predation may have evolved even earlier, as there is summary evidence of predation from the Ediacaran Period, 10-20 million years before the Cambrian-Precambrian boundary.
The last two major evolutionary innovations are the transition to land and the transition to air. The transfer to land is the more important of the two, occurring between about 460 and 430 million years ago, during the Ordovician and Silurian periods. Around this time, green algae evolved into land plants, followed several tens of millions of years later by simple arthropods, including the ancestors of modern spiders and harvestmen. The earliest known terrestrial fossil is a millipede. Much later, about 350 million years ago, during the Carboniferous period, insects evolved flight, exploiting a huge new niche. Flight would evolve independently three more times: in pterosaurs, birds and bats.
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