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The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.
A supercontinent cycle is the break-up of one supercontinent and the development of another, which takes place on a global scale. [4] Supercontinent cycles are not the same as the Wilson cycle, which is the opening and closing of an individual oceanic basin. The Wilson cycle rarely synchronizes with the timing of a supercontinent cycle. [1]
Eurasia (/ j ʊəˈr eɪ ʒ ə / yoor-AY-zhə, also UK: /-ʃ ə /-shə) is the largest continental area on Earth, comprising all of Europe and Asia. [3] [4] According to some geographers, physiographically, Eurasia is a single supercontinent. [4]
The two-domain system is a biological classification by which all organisms in the tree of life are classified into two domains, Bacteria and Archaea. [ 1 ] [ 2 ] [ 3 ] It emerged from development of knowledge of archaea diversity and challenges the widely accepted three-domain system that classifies life into Bacteria, Archaea, and Eukarya . [ 4 ]
Afro-Eurasia (also Afroeurasia and Eurafrasia) is a landmass comprising the continents of Africa, Europe, and Asia. [ 1 ] [ 2 ] The terms are compound words of the names of its constituent parts. Afro-Eurasia has also been called the " Old World ", in contrast to the " New World " referring to the Americas .
A speculatively rooted tree for RNA genes, showing major branches Bacteria, Archaea, and Eukaryota The three-domain tree and the eocyte hypothesis (two-domain tree), 2008. [7] Phylogenetic tree showing the relationship between the eukaryotes and other forms of life, 2006. [8] Eukaryotes are colored red, archaea green, and bacteria blue.
Bacteria are prokaryotic microorganisms that can either have a bacilli, spirilli, or cocci shape and measure between 0.5-20 micrometers. They were one of the first living cells to evolve [9] and have spread to inhabit a variety of different habitats including hydrothermal vents, glacial rocks, and other organisms.
Ur is a hypothetical supercontinent that formed in the Archean eon around 3.1 billion years ago (Ga). In a reconstruction by Rogers, Ur is half a billion years older than Arctica and, in the early period of its existence, probably the only continent on Earth, making it a supercontinent despite probably being smaller than present-day Australia.