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The geological history of the Earth follows the major geological events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers ( stratigraphy ). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left ...
Earth is rounded into an ellipsoid with a circumference of about 40,000 km. It is the densest planet in the Solar System. Of the four rocky planets, it is the largest and most massive. Earth is about eight light-minutes away from the Sun and orbits it, taking a year (about 365.25 days) to complete one revolution.
Universal natural resources and physical phenomena that lack clear-cut boundaries, such as air, water, and climate, as well as energy, radiation, electric charge, and magnetism, not originating from civilized human actions. In contrast to the natural environment is the built environment.
Human physical appearance. Human physical appearance is the outward phenotype or look of human beings. Image of a Caucasian female (left) and an Asian male (right) human body seen from front (upper) and back (lower). Adult human bodies photographed whose naturally-occurring pubic, body, and facial hair have been deliberately removed to show ...
e. Race is a categorization of humans based on shared physical or social qualities into groups generally viewed as distinct within a given society. [1] The term came into common usage during the 16th century, when it was used to refer to groups of various kinds, including those characterized by close kinship relations. [2]
Natural selection acts on an organism's phenotype, or physical characteristics. Phenotype is determined by an organism's genetic make-up (genotype) and the environment in which the organism lives. When different organisms in a population possess different versions of a gene for a certain trait, each of these versions is known as an allele .
The history of Earth is divided into four great eons, starting 4,540 mya with the formation of the planet. Each eon saw the most significant changes in Earth's composition, climate and life. Each eon is subsequently divided into eras, which in turn are divided into periods, which are further divided into epochs . Eon.
The lower mantle, historically also known as the mesosphere, represents approximately 56% of Earth's total volume, and is the region from 660 to 2900 km below Earth's surface; between the transition zone and the outer core. [1] The preliminary reference Earth model (PREM) separates the lower mantle into three sections, the uppermost (660–770 ...