An oven that was filled with earth up to its midpoint: [The area] from the earth and downward contracts tumah via contact; [the area] from the earth and upward contracts tumah via airspace. [If] one placed [an oven] over the mouth of a pit or over the mouth of a cistern and placed a stone there, R’ Yehudah says: If he lights [a fire] below and [the oven] is heated above, it is tamei. But the Sages say: Since in any event [the oven] was heated, it is tamei.