▁pat ented . ▁The ▁mic row ave ▁o ven ▁uses ▁mic row ave ▁radiation ▁to ▁ex cite ▁the ▁mole cules ▁in ▁food ▁causing ▁fr iction , ▁thus ▁producing ▁heat . ▁ ▁Types ▁of ▁o vens ▁▁ ▁Double ▁o ven : ▁a ▁built - in ▁o ven ▁fi xture ▁that ▁has ▁either ▁two ▁o vens , ▁or ▁one ▁o ven ▁and ▁one ▁mic row ave ▁o ven . ▁It ▁is ▁usually ▁built ▁into ▁the ▁kitchen ▁cabinet . ▁ ▁Earth ▁o ven : ▁An ▁earth ▁o ven ▁is ▁a ▁pit ▁d ug ▁into ▁the ▁ground ▁and ▁then ▁he ated , ▁usually ▁by ▁rocks ▁or ▁sm older ing ▁de br is . ▁Histor ically ▁these ▁have ▁been ▁used ▁by ▁many ▁cult ures ▁for ▁cook ing . ▁Cook ing ▁times ▁are ▁usually ▁long , ▁and ▁the ▁process ▁is ▁usually ▁cook ing ▁by ▁slow ▁ro ast ing ▁the ▁food . ▁Earth ▁o vens ▁are ▁among ▁the ▁most ▁common ▁things ▁arch ae olog ists ▁look ▁for ▁at ▁an ▁anth rop ological ▁dig , ▁as ▁they ▁are ▁one ▁of ▁the ▁key ▁indic ators ▁of ▁human ▁civil ization ▁and ▁static ▁society . ▁ ▁Cer am ic ▁o ven : ▁The ▁cer am ic ▁o ven ▁is ▁an ▁o ven ▁constructed ▁of ▁cl ay ▁or ▁any ▁other ▁cer am ic ▁material ▁and ▁takes ▁different ▁forms ▁depending ▁on ▁the ▁culture . ▁The ▁Indians ▁refer ▁to ▁it ▁as ▁a ▁t ando or , ▁and ▁use ▁it ▁for ▁cook ing . ▁They ▁can ▁be ▁dated ▁back ▁as ▁far ▁as ▁ 3 , 0 0 0