studiot Posted September 2 Posted September 2 The stratigraphic record is very sparse to missing for the period when it was thought that there may have been an intense ice age of the magnitude tojustify the name Snowball Earth. This report suggests that this was about 720 mya. It also suggests that the full stratigraphy is to be found on some remote Scottish Islands. https://www.bbc.co.uk/news/articles/cj9l2mrn43jo Quote A cluster of Scottish islands could help solve one of our planet's greatest mysteries, scientists say. The Garvellach islands off the west coast of Scotland are the best record of Earth entering its biggest ever ice age around 720 million years ago, researchers have discovered. The big freeze, which covered nearly all the globe in two phases for 80 million years, is known as "Snowball Earth", after which the first animal life emerged. Clues hidden in rocks about the freeze have been wiped out everywhere - except in the Garvellachs. Researchers hope the islands will tell us why Earth went into such an extreme icy state for so long and why it was necessary for complex life to emerge. 1
sethoflagos Posted September 2 Posted September 2 1 hour ago, studiot said: The stratigraphic record is very sparse to missing for the period when it was thought that there may have been an intense ice age of the magnitude tojustify the name Snowball Earth. This report suggests that this was about 720 mya. It also suggests that the full stratigraphy is to be found on some remote Scottish Islands. https://www.bbc.co.uk/news/articles/cj9l2mrn43jo Not sure the BBC really do this story full justice. Original JGS open access article and pdf download at https://www.lyellcollection.org/doi/full/10.1144/jgs2024-029 1
exchemist Posted September 4 Posted September 4 On 9/3/2024 at 12:05 AM, sethoflagos said: Not sure the BBC really do this story full justice. Original JGS open access article and pdf download at https://www.lyellcollection.org/doi/full/10.1144/jgs2024-029 Thanks for digging out the paper. I happen to be in Scotland this week so it was interesting to read and to see the diagrams of the geology of the Highlands between the two great faults. They seem to have sampled not only the Garvellach islands but also Islay and a location in Donegal in N Ireland where the same formation outcrops. (It’s rather romantic that they call these rocks the Dalradian sequence, after the ancient Irish/Scottish kingdom of Dalriada which encompassed both N Ireland and W Scotland.) It seems the rocks in question are alternating layers of “diamictite”, a poorly sorted sedimentary conglomerate associated with glacial moraines, and sandstone, which of course is homogeneous and laid down in a marine environment. So it looks as if at wherever on the globe these rocks were laid down, it was by no means one solid era of glaciation at the (near equatorial?) latitude in question. interesting too for me to see how they get a fix on the earliest and latest date for the age of the sequence by radiometric dating of volcanic intrusions and volcanic ash deposits.
sethoflagos Posted September 4 Posted September 4 4 hours ago, exchemist said: I happen to be in Scotland this week so it was interesting to read and to see the diagrams of the geology of the Highlands between the two great faults. If you've not come across it already, you might find this online geological map of interest at https://www.bgs.ac.uk/map-viewers/bgs-geology-viewer/
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