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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]
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]
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 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.
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 ]
[45] [46] However, a few biologists argue that the Archaea and Eukaryota arose from a group of bacteria. [47] In any case, it is thought that viruses and archaea began relationships approximately two billion years ago, and that co-evolution may have been occurring between members of these groups. [ 48 ]
A lack of international leadership, President-elect Donald Trump's second term and AI all made the list of the biggest risks the world faces in 2025, according to the Eurasia Group, which is a ...
Asia and Europe are considered separate continents for historical reasons; the division between the two goes back to the early Greek geographers. In the modern sense of the term "continent", Eurasia is more readily identifiable as a "continent", and Europe has occasionally been described as a subcontinent of Eurasia. [68]