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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 impres

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. [1] https://news.ycombinator.com/item?id=14014049 https://news.ycombinator.com/item?id=14014049 [2] https://www.discovermagazine.com/planet-earth/get-lost-in-mega-tunnels-dug-by-south-american-megafauna https://www.discovermagazine.com/planet-earth/get-lost-in-me...

throwaway_pdp09 6y ago
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?)
- ajb 6y ago
  Well, if it's limestone, maybe they used urine.
  - throwaway_pdp09 6y ago
    Too slow. Assuming that was a serious suggestion anyway.
- cbkeller 6y ago
  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] [1] https://www.cambridge.org/core/journals/clay-minerals/article/minerals-in-the-clay-fraction-of-brazilian-latosols-oxisols-a-review/D7F78269F40171B35BDF5FFCFD9EB5B7 https://www.cambridge.org/core/journals/clay-minerals/articl... [2] https://en.wikipedia.org/wiki/Duricrust https://en.wikipedia.org/wiki/Duricrust [3] https://www.sciencedirect.com/science/article/pii/S0169136817309587 https://www.sciencedirect.com/science/article/pii/S016913681... [4] https://www.sciencedirect.com/science/article/abs/pii/S0012821X1200101X https://www.sciencedirect.com/science/article/abs/pii/S00128...
  - throwaway_pdp09 6y ago
    A Most Excellent answer, thanks!
bookofjoe 6y ago
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.
pvaldes 6y ago
I still think that there are alternative, evident and simpler explanations for this tunnels.
- deleted 6y ago
  [deleted]

throwaway_pdp09 6y ago

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?)

ajb 6y ago
Well, if it's limestone, maybe they used urine.
- throwaway_pdp09 6y ago
  Too slow. Assuming that was a serious suggestion anyway.
cbkeller 6y ago
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] [1] https://www.cambridge.org/core/journals/clay-minerals/article/minerals-in-the-clay-fraction-of-brazilian-latosols-oxisols-a-review/D7F78269F40171B35BDF5FFCFD9EB5B7 https://www.cambridge.org/core/journals/clay-minerals/articl... [2] https://en.wikipedia.org/wiki/Duricrust https://en.wikipedia.org/wiki/Duricrust [3] https://www.sciencedirect.com/science/article/pii/S0169136817309587 https://www.sciencedirect.com/science/article/pii/S016913681... [4] https://www.sciencedirect.com/science/article/abs/pii/S0012821X1200101X https://www.sciencedirect.com/science/article/abs/pii/S00128...
- throwaway_pdp09 6y ago
  A Most Excellent answer, thanks!

bookofjoe 6y ago

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.

pvaldes 6y ago

I still think that there are alternative, evident and simpler explanations for this tunnels.

deleted 6y ago
[deleted]