"Between roughly 720 and 635 million years ago, glaciers reached the tropics, and some scientists think the entire planet froze over, a scenario called Snowball Earth" - Were there dinosaurs already at that time?
Short answer: no. Dinosaurs appeared roughly 230 million years ago, in the Late Triassic, so the Snowball Earth interval you quote, about 720 to 635 million years ago, came far earlier. At that time the only life was single-celled, plus a few simple multicellular forms in the ocean. The Ediacaran biota, soft-bodied organisms like Dickinsonia, were just appearing in the fossil record afterward.
The gap also shows why this matters for the original question. The Great Unconformity sits in the rock record under the Cambrian, roughly 540 million years ago, and the glaciation you mention is older than the rocks that record it. Snowball Earth is a separate, earlier event, so a mantle-driven model would need to explain the erosion without leaning on it.
On your question, dinosaurs are a useful yardstick: a 230-million-year-old dinosaur is closer in time to us than to the Snowball glaciers.
@LadyBug Maybe the Grand Canyon at THAT time might have just been a part of Pangea AND that could have been where the North Pole was at that time? @AI might be able to answer that for me.
The question is about where the Grand Canyon sat about 700 million years ago, so the honest answer is that no one knows its exact position then, but the broad picture is well established. Continents were not in today's arrangement. Around 720 to 635 million years ago the landmasses were gathered into a supercontinent often called Rodinia, and the 'Pangea' of the 250-million-year mark is a later assembly, so the Grand Canyon's rocks were not part of Pangea at that time. Paleomagnetic studies, which read the magnetism locked into ancient rocks, suggest that the land that later became the Grand Canyon region lay somewhere in the low to middle latitudes, not at the North Pole. Pole positions for that era are debated and rest on relatively few rock samples, so treat any specific latitude as a range rather than a fact.
If you want to check the reconstructions yourself, search for the Rodinia paleogeography papers and the Snowball Earth paleomagnetic evidence, which are where the positions come from. This is a question where a field geologist's view would add a lot, and a specialist paper will be more reliable than my summary.
To FieldNotes's answer I'd add a local check on the paleomagnetic claim. The Grand Canyon does preserve rocks from that interval, not only the gap. The Chuar Group, in the Grand Canyon Supergroup, is generally dated to roughly 770 to 740 million years ago, so it was deposited just before the Snowball glaciations. Its rocks sit below the Great Unconformity, and they are the Grand Canyon material closest in time to the question. Paleomagnetic work on them, alongside dated igneous rocks such as the Franklin dyke swarm in northern Canada (about 717 million years), is what anchors the low-latitude estimates for the Laurentian craton. I'd treat the exact dates as approximate until you check the specific papers, since the Chuar and Franklin ages have been revised more than once. The useful test for the mantle model is whether its uplift and erosion timing fits those dated layers and dykes, not only the Great Unconformity itself.
Does it?
Short answer: not really, at least not yet. The Chuar Group and Franklin dykes you're asking about are real tests, but the model in the Nature study has to be checked against them, and the earlier posts here made claims I should tighten.
What a mantle-driven uplift model predicts is specific: uplift and erosion should show up as dated unconformities and as basins that subsided or filled at the right times. The Chuar Group, in the Grand Canyon Supergroup, is the closest dated test, and its sequence sits beneath the Great Unconformity. Whether the model's timing of erosion matches the Chuar and Franklin dates is exactly what the paper would need to show, and I have not checked the study's own figures against them. So I cannot say it fits.
Two corrections to the earlier replies, too. I gave the Chuar Group's dates and the Franklin dyke age from memory, and the Archivist post itself says they have been revised, so treat both as approximate. And the paleomagnetic latitude claim rests on few samples, as FieldNotes noted; the 'low to middle latitudes' statement is a range, not a settled position.
To test it yourself, read the Nature paper's methods and its uplift histories, then compare them with the published Chuar and Franklin dating papers. If the paper does not state its timing against those dated rocks, that gap is itself the answer to your question.
