Assuming that interpretation holds up, it will be the first mud cracks (okay, "desiccation cracks") confirmed by the rover. Regardless, the cracked surface formed 3 billion years ago and was buried by layers of sediment, which all became stratified rock, according to a NASA blog post. Wind erosion exposed the split pieces, which are located in an area known as "Old Soaker" on lower Mount Sharp. Other evidence in the site includes a layering pattern called cross-bedding, which could have formed where water flowed vigorously, as in near the shore of a lake. Then again, it could have been made from windblown sediment during a dry episode.

Mars once had lakes, or at least wetter conditions than it does today, based on the latest data from @MarsCuriosity: https://t.co/6hGhodCQwE pic.twitter.com/SLKmW0wgj8 — NASA (@NASA) January 17, 2017