Although smaller, colder and with a much thinner atmosphere, Mars is still similar to Earth in many ways. I was reminded of that again a few days ago when I came across an interesting photo while looking for iPhone/iPad wallpaper backgrounds. I don’t know the location or who took the photo (if anyone does, please let me know), but the image shows a very good example of “mud polygons” or mud cracks where muddy sediments have dried out, forming a polygonal network of cracks (of various types).
I immediately noticed the similarity to the fractured sulphate bedrock which is extensive in Meridiani where the Opportunity rover is on Mars. While the composition may be different, both are sedimentary bedrock, not volcanic. The processes forming them may be quite similar, as it had been determined by rover scientists, from evidence found by Opportunity, that the region once had near-surface groundwater and even shallow, although perhaps temporary, pools or playa lakes of surface water (albeit salty and acidic). A couple examples of the Meridiani terrain are below (the second one taken just a few days ago):
Similar terrain can also be the result of repetitive freezing/thawing, such as the ice-wedge polygons in the Arctic. Whichever process may actually be responsible for the Meridiani polygons, the similarity to familiar geology on Earth is another example of how Mars, while quite alien in some ways, is remarkably Earth-like in others.
Thanks also to the guys on the Mars Forum for their assistance with this.