finally they said it concerned something between 4 and 6 thousand years ago.
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Based on bits of detritus they could carbon date. But that does not square with the orientation of the feature which is oriented to the stars of 150 million years ago - as I read it.
Those sorts love to keep the status quo and will say anything, attach any number, etc, to maintain it. For them its simply impossible that any civilization could have existed 150 million years ago - because as we all ‘know’ that in 4.5 billion years the Earth is said to have been around, only one civilization could have arisen - ours.
If our civilization ended now, in 20,000 years there would be no detectable trace. Keep in mind that, until a decade ago, these same people said there were no civilizations prior to the Sumerians - which we now know to be false having found Gobekli Teppi at 12,500 years before present. So how many could have arisen in 150,000,000 years and have left nothing to be found except some stones and earth works? Stones and earthworks get repurposed all the time - so its surprising they found this one.
If built 150 million years ago, even postulating intelligent dinosaurs, that circle would no longer exist. Given that the direction of true north pivots completely roughly every 26,000 years there is no way to say what the earth’s orientation was 150M years ago. It is true a lot of useful work has yet to be done on possible civilization remains under water, but so far as knowledge about early civilizations other than Sumerian being only a decade old, that is not true. I first became interested in ancient civilizations about 70 years ago. Over the following years I was delighted to learn about the Indus Valley cultures, and the much older Clovis culture in North America. Granted archeology science was a little slow to get off the nothing before Clovis pot, but individuals were fighting that 40 years ago. Then on the East Coast I met a California scientist who was part of a small group trying to achieve recognition of remains that might have been closer to 200,000 years old.
We know that for the past million years earth has cycled through warm and ice age cycles at roughly 125,000 year intervals. I think it is certainly possible that in the short warm periods some hominids could have achieved a Stonehenge level of sophistication (which was a bit older than Sumer), but geological processes would have destroyed, buried, or drowned.
If you want a real puzzle no one seems to be working on these days, check out the area in Africa below the Okavanga Delta. I spent a number of hours using Goodle Earth to survey an amazing pattern of one mile separated ditches that covers an area more than 400 miles by 400 or more miles. No one is apparently studying this huge complex. With Google Earth you can come down to 50 or 100 feet above land. My thought was how many years and laborers would it take to dig so many ditches so wide, deep, and long. Some areas seem much older and worn down than others, and I saw a suggestion some might be 20,000 or more years old. My guess is that what ever culture(s) were doing this did it for the common good of having water filled channels year round. No authoritarian rulers with big palaces visible there. Perhaps some of the big project thinkers finally moved east and built Great Zimbabway. Always fun to speculate.