If Erathostenes was off by only 40 miles out of about 4,000 miles for the radius, then he was off by 1 part per 100. It does not seem that difficult to imagine that the Egyptians, being the very precise measurers of astronomy that they were, were able to have an accuracy that was ten times better, being off by only about 4 miles out of about 4,000 miles.
I haven't read the reports on Erathostenes actual work in many years, and I don't actually recall exactly what his results were, only that they were valid, but not real close due to his lack of precision. He likely only did the measurement once, after having been inspired (quite possibly by locals who told him about legends of their ancestors), before returning to his native land of Greece. Doing the measurement repeatedly, under precise conditions, would likely give greater precision, comparable to what the Egyptians were in fact able to achieve (Earth's radius accurate to 1 part per 1,000).
The Visitor makes a cogent comment about our base-12 counting system we clearly initially used.
12 blocks of 440 feet = 5280 feet = 1 British Mile
1760 RC = 4 X 440 RC = Perimeter of Base of GP = 1 "Egyptian Mile"
1760 Yards = 4 X 440 Yards = 1 British Mile
How many Pence to the Shilling, 12?
16 Shillings to the Pound, though, just like 16 Ounces to the Quart (I know, Britain went metric since I was there last.)
So, what were the other systems of linear measurement in ancient times?
We have the Royal Cubit that was used extensively for millenia, in Egypt and nearby areas.
We have the Scientific Cubit that was developed, then abandoned almost immediately and completely forgotten about until the 1800s A.D. when re-discovered by an examination of the interior of the GP.
We have the Yard, which might be originally based on 3 X 12 scientific-inches, though its origin otherwise remains obscure.
We have the Meter, which was developed in the late 1700s, almost exactly in the same manner as the scientific cubit, but using the 1/10,000,000th of the 1/4 circumference of Earth, rather than the 1/10,000,000th of the radius of Earth.
What systems of measurement were in use in Persia, in Mesopotamia, in Asia, in Greece, in Rome, in the Americas, etc.? Do we have these known as accurately as the RC (which is likely defined by scholars as the 1/1760th of the Base Perimeter of the GP)?
I would be interested in reading more about ancient maps, particularly if any show former sea-levels. Are any of these proven to be non-fake, and published in recognized literature? It is not implausible that ancient peoples were navigating the oceans in large ships. Large ship births were discovered decades ago in India (though I'm not certain if they were well dated other than being from ancient times) that accomodated ships that would dwarf those of the Phoenicians and Greeks.
We are constantly discovering that ancient peoples were more advanced than previously believed in many ways. A recent find of a Greek shipwreck included a multi-geared (30+ gears?) metal calculator from circa 300 B.C.
And, finally, in answer to a question posed - when do you believe the Ice Ages ended? The answer is - they haven't.
We are still in the midst of an Ice Age - the glaciers have only half-melted, raising the sea level some 400 feet. There is another 400 feet to go before the Ice Ages are ended.
Currently, we are in a 'lull' of melting, just as there have been numerous other 'lulls' in which the sea level stabilizes for centuries or millenia, then the melting resumes. Then again, it might return to a full Ice-Age without undergoing the complete melt-down, as has repeatedly occurred eons ago.
Time will tell.
Laika's comments appear valid, particularly with tree-ring dating. I do not believe there would have been two growing cycles in one year during any time in the past dozen millenia that would have thrown off that counting method. There is always some addition of fossil carbon to the atmosphere, from volcanoes, methane hydrate releases, etc. There is no recorded spike of such Carbon release, however, until the present times with the large spike due to industrialization. However, there might be some error in dating the phases of melting of the glaciers, and it's possible there's even been some small (a few feet) rise in the sea levels during the past few millenia, though our recent records for the past few centuries show them stable. Generally, however, it is believed we were in a full Ice-Age (sea levels 400 feet lower than presently) for many millenia (100,000 years +?), and indeed for most of humanity's 'pre-history', before the start of the melt down commenced roughly 18,000 years ago. Perhaps it will take another 18,000 years to complete the melt-down.
The Visitors comments about giants continues to be intriguing. We know that such types came into existence in the ancient past, the most famously documented being Goliath of the David-and-Goliath fame in the Bible story.
If there was another race of people (just as the Neanderthals were another race of 'people'), clearly we would have been 'at war' with them (since we've always been 'at war' with some tribe or another, amongst ourselves). It is not beyond the realm of possibility that a mutant race also arose from earlier humans, that included gigantism and polydactyly. However, The Visitor has the terrible habit of telling us about all of his interesting readings, but never citing any of them.
That double-row-of-dentition sounds like an aberrant mutation, since all other hominid species, going back millions of years, always have single rows. I'd need to see a skull or other proof, not just an anecdotal report. As they say in Missouri, show me.