Great article, but the ending made little sense: We all chuckled at this prediction—mass extinction, by this point, having become something of a macabre inside

Great article, but the ending made little sense: We all chuckled at this prediction—mass extinction, by this point, having become something of a macabre inside joke. Just past the spoil, we reached the end of the road, which was lined with piles of white dirt too tall to see over. Clambering over them in search of outcrops, we were confronted by a strange view on the other side: an enormous field of coal, pockmarked with holes. The black earth had been dug at regular intervals to create thousands of pits, all the size and depth of shallow graves. Each one had its own mound of white earth beside it, as if waiting to be filled. No one could explain what they were. This has little to do with the rest of the article, raises a whole slew of questions, and the phrase "no one could explain what they were" is uncharactersitically vague. It feels like I missed the punchline to a joke. I can imagine the kinds of debates about the origins of the pits might resemble the debate about the impact theory, but this indirection seems like an odd way to end an otherwise clearly written article. What am I missing?