Well, I think moist cracks deep within the bedrock would be a more hospitable location for microbes than the surface. Less radiation, probably warmer, and a much better chance of finding water (liquid or solid) than on the surface.

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The quarrelsome oarsmen were rowing,
The great violinist was bowing;
But how is the sage
To tell, from the page:
Was it pigs or seeds that were sowing?