Geologist here! A fun fact that has received some previous discussion [1] here:
Some of these same missing megafauna (likely giant ground sloths) dug an impressive network of several-meter-diameter tunnels through the unusually stable, iron-rich soils of southern Brazil, which survive to this day [2].
You can actually go and walk through these burrows, despite the fact that the species who dug them are long-extinct.
Totally amazing and wonderful. Though I've only been awake about 30 minutes, I'm willing to go out on a limb and say this will prove to be the best thing I learn today.
Saw the original HN link and was blown away, however there's a question that you as a geologist may be able to answer - how can nails (basically sloth fingernails) possibly compete with anything but soil? This (link 2) looks like sandstone and that's strong (relatively) and damn abrasive. I can't see it.
BTW that can't be soil, it would have collapsed (surely?)
They're soils, but they're special soils [1] that can harden to a brick-like consistency (called a "duricrust") upon being dried out and exposed to the air [2,3].
The unusual durability of such soils has made them a target for study in their own right, using cosmogenic isotopes to estimate erosion rates over Myr timescales (which turn out to be incredibly slow; 0.16–0.54 m/Myr) [4]
Some of these same missing megafauna (likely giant ground sloths) dug an impressive network of several-meter-diameter tunnels through the unusually stable, iron-rich soils of southern Brazil, which survive to this day [2].
You can actually go and walk through these burrows, despite the fact that the species who dug them are long-extinct.
[1] https://news.ycombinator.com/item?id=14014049
[2] https://www.discovermagazine.com/planet-earth/get-lost-in-me...