Assertion: magma | /r/HasProperty | formed over considerable length of time
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text: Simply put, magma is formed when solid rock and other constituents in the upper mantle or lower crust melts as the result of heat and pressure exerted upon them over a considerable length of time by a number of factors including ‘hotspots’, which are areas where the much hotter lower mantle effectively superheats the cooler material of the upper mantle and lower crust above and melts them.