A different twist on the contangion scenario

[pmulcahy11b]

It is 2025. Man has successfully sent human beings to Mars, and brought them back safely. They also brought back microbial life which is fatal to most Earth life -- some of the astronauts are already carrying the microbes, though they have not exhibited any symptoms yet. The biological detectors are not set up properly to register the Martian microbes. And it gets out into the world. Within a year, the earth is a wasteland of dead human, plant, and animal life, with only a few pockets of resistant humans, plants, and animals remaining.

Yes, I know that it's a scientifically sketchy idea. But it's just an idea.