Earthly means happening in the material world of our life on earth and not in any spiritual life or life after death. 尘世的
adjective [原级]地球的;尘世的;可能的
The elder brother is issuing this theory without any consideration—obviously, whatsoever of earthly reality and we're shocked by. 哥哥在发表这个理论的时候显然没有考虑任何惊世骇俗的现实。