8 ms·

I also have a question. the article references the discovery of the new crater created by meteorite hitting Greenland https://www.nationalgeographic.com/scienc

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-crater-found-under-hiawatha-glacier-greenland-ice/ https://www.nationalgeographic.com/science/2018/11/impact-cr... 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 8y ago
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/JB076i023p05683 https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JB07... [2] https://www.sciencedirect.com/science/article/pii/S0012821X02011524 https://www.sciencedirect.com/science/article/pii/S0012821X0...

8 ms·

I also have a question. the article references the discovery of the new crater created by meteorite hitting Greenland https://www.nationalgeographic.com/scienc

by 75dvtwin 8y ago

cbkeller 8y ago
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/JB076i023p05683 https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JB07... [2] https://www.sciencedirect.com/science/article/pii/S0012821X02011524 https://www.sciencedirect.com/science/article/pii/S0012821X0...