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The Precambrian is an informal unit of geologic time, [3] subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.6 billion years ago ( Ga ) to the beginning of the Cambrian Period, about 538.8 million years ago ( Ma ), when hard-shelled creatures first appeared in ...
Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. According to modern evolutionary biology, all living beings could be descendants of a unique ancestor commonly referred to as the last universal common ancestor (LUCA) of all life on Earth.
Date Event 4.3-4.1 Ga The earliest life appears, possibly as protocells.Their genetic material was probably composed of RNA, capable of both self replication and enzymatic activity; their membranes were composed of lipids.
The Neanderthal DNA found in modern human genomes has long raised questions about ancient interbreeding. New studies offer a timeline of when that occurred and when ancient humans left Africa.
The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth.Dates in this article are consensus estimates based on scientific evidence, mainly fossils.
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 ...
Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
His formal test favoured the existence of a universal common ancestry over a wide class of alternative hypotheses that included horizontal gene transfer. Basic biochemical principles imply that all organisms do have a common ancestry. [71] A proposed, earlier, non-cellular ancestor to LUCA is the First universal common ancestor (FUCA).
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