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Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from matter that does not. It is defined descriptively by the capacity for homeostasis, organisation, metabolism, growth, adaptation, response to stimuli, and reproduction.
Insects roamed the land and would soon take to the skies; sharks swam the oceans as top predators, [83] and vegetation covered the land, with seed-bearing plants and forests soon to flourish. Four-limbed tetrapods gradually gain adaptations which will help them occupy a terrestrial life-habit. 360 Ma First crabs and ferns.
The result of four billion years of evolution is the diversity of life around us, with an estimated 1.75 million different species in existence today. [71] [72] Usually the process of speciation is slow, occurring over very long time spans; thus direct observations within human life-spans are rare.
The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. [1] [2] [3] The similarities among all known present-day species indicate that they have diverged through the ...
Evolution is the change in the heritable characteristics of biological populations over successive generations. [1] [2] It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. [3]
The scientific revolution, which began to take hold in the 17th century, represented a sharp break from Aristotelian modes of inquiry. [66] One of its principal advances was the use of the scientific method to investigate nature. Data was collected, and repeatable measurements were made in experiments. [67]
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Phylogenetic trees of species and higher taxa are used to study the evolution of traits (e.g., anatomical or molecular characteristics) and the distribution of organisms (biogeography). Systematics, in other words, is used to understand the evolutionary history of life on Earth.