Dr. Jack Farmer, of NASA's Ames Research Center, commented to a January 1996 Ciba Foundation-organized international meeting in London about possible problems connected with the fossil evidences of previous life that are to be searched for on Mars during upcoming Mars missions.
They may have links to Earth. In 1911, a dog in Egypt was killed by a piece of the "Red Planet," assumedly the byproduct of a cometary impact on Mars which splashed material here.
It is possible that life could have been transferred either way as well. Nevertheless, the NASA missions will have to be concerned with any gathered samples which might have viable spores, microbes or bacteria--and could contaminate the Earth. Dr. Farmer spoke at the meeting of such "important ethical concerns."
Life may well have manifested on a warmer and moister Mars some three to four billion years ago. However, if Martian life still exists, it may be as hardy as hyperthermophiles, microbes which consume rocks and water and which live deep beneath north Alaska. Richland's Pacific Northwest Laboratory, which found them, has been studying these lifeforms, which can survive in Marslike conditions between 85 degrees Centigrade and 113 degrees Centigrade.