
Earth is missing a huge part of its crust. Now we may know why - cbkeller
https://www.nationalgeographic.com/science/2018/12/part-earths-crust-went-missing-glaciers-may-be-why-geology/
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cbkeller
I'm the first author of the relevant study [1] (open-access) so I'm biased to
think this is cool. The unconformity certainly isn't everywhere (in some
places there is no missing crust or time at all), but it can be found on just
about every continent, and there has been surprisingly little previous
quantification of this. Happy to answer any questions if anyone's interested.

[1]
[https://www.pnas.org/content/early/2018/12/26/1804350116](https://www.pnas.org/content/early/2018/12/26/1804350116)

~~~
75dvtwin
I also have a question. the article references the discovery of the new crater
created by meteorite hitting Greenland

[https://www.nationalgeographic.com/science/2018/11/impact-
cr...](https://www.nationalgeographic.com/science/2018/11/impact-crater-found-
under-hiawatha-glacier-greenland-ice/)

would the erosion caused by glaciers, have enough time to erase the planet-
wide evidence of that hit as well?

What conditions need to be there for the erasure to work quickly?

~~~
cbkeller
Ah yeah. That crater is about 30 km wide, which is pretty big. Most craters
follow roughly a 1:10 scaling between depth and diameter [1], so we can
approximate a 3 km initial depth for this new new Hiawatha Crater. This crater
is quite young (12 ka to 3 Ma est.), but if it had existed 720 Myr ago, then
our estimates suggest it would have been borderline -- probably erased unless
it got lucky and landed in one of the regions with little or no Neoproterozoic
glacial erosion

The number one condition for fast glacial erosion is what's called "wet-based
ice": if pressure and temperature at the base of the ice sheet (warmed by
geothermal heat flow) is near the melting point, then ice tends to slip
against the rock and erode rapidly; if it's too cold, then the ice will flow
internally instead and not erode very well. Coupled climate-icesheet models so
far [2] suggest it's possible to get wet-based ice even in a "hard snowball"
state with limited precipitation from sublimation alone (though not under all
parts of the icesheet at once).

[1]
[https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JB07...](https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JB076i023p05683)
[2]
[https://www.sciencedirect.com/science/article/pii/S0012821X0...](https://www.sciencedirect.com/science/article/pii/S0012821X02011524)

