| Great question -- and yes! Pleistocene glaciation in the northern hemisphere has been a lot shorter (so far) than the Cryogenian glaciations, but it is probably not a coincidence that the outline of Canada's "Precambrian shield" basically matches the outline of the Laurentide ice sheet (check out Figure 5 of the 2019 paper [1]). We're probably only talking about scraping off no more than a couple hundred meters of sedimentary rock formerly covering the shield, but that's about what you'd expect. More broadly, as one author noted long before us [2] it turns out that most of the places on Earth where there is a lot of Precambrian crystalline basement exposed at the surface today (i.e., where later sedimentary rocks have been scraped off, one way or another) were glaciated either recently or in the Late Paleozoic Ice Age [3], which hit much of Gondwana (see also Fig S16 here [4]). More recently, another group of researchers using thermochronology in Antarctica [5] found evidence of several kilometers of exhumation during the Late Paleozoic Ice Age, as well as perhaps 1-2 km during the last ~35 Myr of Cenozoic glaciation (n.b., Antarctica has been glaciated for a good bit longer than we've been having ice ages in the northern hemisphere). [1] https://www.pnas.org/content/116/4/1136/tab-figures-data and see also Fig S16 in [4] [2] https://pubs.geoscienceworld.org/gsa/gsabulletin/article/83/... [3] https://en.wikipedia.org/wiki/Late_Paleozoic_icehouse [4] https://www.pnas.org/content/pnas/suppl/2018/12/26/180435011... [5] https://doi.org/10.1016/j.epsl.2018.10.044 (see especially Fig. 7) |