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If replacement level fertility is sustained over a sufficiently long period, each generation will exactly replace itself. [10] The replacement fertility rate is 2.1 births per female for most developed countries (in the United Kingdom , for example), but can be as high as 3.5 in undeveloped countries because of higher mortality rates ...
118 chemical elements have been identified and named officially by IUPAC.A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z).
GW170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy NGC 4993, about 140 million light years away.