No. 17: Fall 1981
The shergottites and nakhlites are two types of meteorites that have scientists scratching their heads. Both types have been dated by various radioactive clocks at 1,300 million years or less -- far younger than all other meteorites. Where could such young meteorites have originated? The asteroids and moon's surface are far too old. A current guess is the surface of Mars. There, an impacting meteor could have blasted pieces of young lava sheets in space and thence to earth. The shergottites have a shocked structure and could well have originated in such catastrophism, but the nakhlites show no signs of violence and seem to require a separate explanation.
(Anonymous; "Mystery Meteorites May Come from Mars," New Scientist, 91:219, 1981.)