About a billion years later, simple life had evolved from non-living chemicals, and precipitated carbonate minerals and organic compounds. Some of these tiny micro-organisms became fossilized, attached to the rock. When a large comet or meteorite struck Mars, some 16 million years ago, it ejected this rock out in space where it floated in a total vacuum until 13,000 years ago when it entered earth's atmosphere as a fireball, landing in Antarctica. Let's look at several features, separating the precise and presumably accurate scientific observations from the interpretations reported by the press. The Viking Lander in 1976 radioed back some chemical data, but not enough to uniquely identify Martian rocks.
Radioisotope dating methods are notoriously unreliable.
The physics of this is possible, but tenuous. One must have good evidence before proposing such a long shot. NASA had previously scheduled another space probe to Mars in November 1996. President Clinton was briefed the week before the August 7 announcement and called for a planning session and additional funding. As you might imagine, the media is making more of this story than the more cautious scientists, many of whom disagree.