▁consists ▁of ▁contin ents ▁and ▁islands , ▁with ▁most ▁of ▁the ▁inhab ited ▁land ▁in ▁the ▁Northern ▁Hem is phere . ▁ ▁Earth ▁has ▁evol ved ▁through ▁ge ological ▁and ▁bi ological ▁processes ▁that ▁have ▁left ▁traces ▁of ▁the ▁original ▁conditions . ▁The ▁outer ▁surface ▁is ▁divided ▁into ▁several ▁gradually ▁migr ating ▁t ect onic ▁pl ates . ▁The ▁interior ▁remains ▁active , ▁with ▁a ▁thick ▁layer ▁of ▁pl astic ▁mant le ▁and ▁an ▁iron - filled ▁core ▁that ▁generates ▁a ▁magnetic ▁field . ▁This ▁iron ▁core ▁is ▁composed ▁of ▁a ▁solid ▁inner ▁phase , ▁and ▁a ▁fluid ▁outer ▁phase . ▁Con ve ct ive ▁motion ▁in ▁the ▁core ▁generates ▁electric ▁curr ents ▁through ▁dynam o ▁action , ▁and ▁these , ▁in ▁turn , ▁generate ▁the ▁geom agnet ic ▁field . ▁ ▁The ▁atmos pher ic ▁conditions ▁have ▁been ▁significantly ▁alter ed ▁from ▁the ▁original ▁conditions ▁by ▁the ▁presence ▁of ▁life - forms , ▁which ▁create ▁an ▁e colog ical ▁balance ▁that ▁stabil izes ▁the ▁surface ▁conditions . ▁Despite ▁the ▁wide ▁regional ▁variations ▁in ▁climate ▁by ▁latitude ▁and ▁other ▁ge ographic ▁factors , ▁the ▁long - term ▁average ▁global ▁climate ▁is ▁quite ▁stable ▁during ▁inter g la cial ▁periods , ▁and ▁variations ▁of ▁a ▁degree ▁or ▁two ▁of ▁average ▁global ▁temperature ▁have ▁histor ically ▁had ▁major ▁effects ▁on ▁the ▁e colog ical ▁balance , ▁and ▁on ▁the ▁actual ▁ge ography ▁of ▁the ▁Earth . ▁ ▁Ge ology ▁ ▁Ge ology ▁is ▁the ▁science ▁and ▁study ▁of ▁the ▁solid ▁and ▁liquid ▁matter ▁that ▁constit