There’s a good debate about this on the subreddit; see also Robin Hanson and Samo Burja.

You can separate these kinds of claims into three categories:

1. Civilizations about as advanced as the people who built Stonehenge

2. Civilizations about as advanced as Pharaonic Egypt

3. Civilizations about as advanced as 1700s Great Britain

The debate is confused by people doing a bad job clarifying which of these categories they’re proposing, or not being aware that the other categories exist.

2 and 3 aren’t straw men. Robert Schoch says the Sphinx was built in 9700 BC, which I think qualifies as 2. Graham Hancock suggests “ancient sea kings” drew the Piri Reis map which seems to depict Antarctica; anyone who can explore Antarctica must be at least close to 1700s-British level.

I think there’s weak evidence against level 1 civilizations, and strong evidence against level 2 or 3 civilizations.

Argument 1: Where Are The Sites?

Supporters of ice age civilizations argue that sea level rose 120 meters as the Ice Age glaciers melted, flooding low-lying coasts and destroying any evidence of coastal civilizations.

What would happen to the ancient civilizations we know about if sea level rose an additional 120m? We would lose Babylon, Rome, and most of Egypt. But:

• The Acropolis of Athens is 150m above sea level, and would be preserved for future archaeologists. Sparta (200m) and Thebes (250m) would also be fine.

• The Hittite capital of Hattusa is almost 1,000m above sea level and would be totally unaffected.

• The two biggest cities in Assyria, Ashur and Nineveh, would both make it.

• Zhengzhou, the capital of the Shang in ancient Chinese, would survive.

• Mojeno-Daro would sink, but Harappa would be fine.

• Basically nobody in Elam/Medea/Persia would even notice.

• The top 80m of the Great Pyramid would rise above the waterline, forming a little island. The part of the Pyramid above the water would still be taller than the entire Leaning Tower of Pisa. It would be pretty hard to miss!

So a 120m sea level rise wouldn’t be enough to wipe out evidence of our crop of ancient civilizations, and shouldn’t be enough to wipe out evidence of a previous crop, unless they had a very different geographic distribution than ours.

Argument 2: Where Are The Crops And Livestock?

We can do genetic analysis of crops and livestock, compare them to wild plants and animals, and make good guesses about where and when they were domesticated.

Wheat was domesticated somewhere around Karaca Dag, Turkey, around 9000 BC. Barley was domesticated somewhere around Jarmo, Iraq, around 9000 BC. Cows were domesticated somewhere around Cayonu Tepesi, Iraq, in 8500 BC (then a second time, in Pakistan, later on). Rice was domesticated in two places in China around 10,000 BC.

All of these crops were invented exactly where the standard historical narrative says there were late pre-agricultural people of exactly the type who would domesticate crops. They spread at about the same rate as sedentary living in general, monuments, and other signs of complex civilization. The only known exception is Gobekli Tepe, a megalithic site in Turkey, which may very slightly predate known agriculture. But it also might very slightly post-date known agriculture, or exactly-date known agriculture (it’s just sixty miles from Karaca Dag, and it would make sense if they were the people who domesticated wheat). That one anomaly aside, there’s a very tight agriculture <—> things that seem to require agriculture coupling.

So if there were Ice Age civilizations, what did they eat? It couldn’t have been any of our known crops, which post-date them. Could it have been their own crops, which were later lost? Seems unlikely. Throughout most of history, civilizations have risen and fallen, but they don’t lose agriculture! The empire divided longs to unite, the empire united longs to divide, but the Chinese never fragment so hard that they forget how to cultivate rice and rice goes extinct. Maize has survived nine millennia of rising and falling bloodthirsty Mexican empires. Almost everyone in the Amazon died in the 1500s when European diseases swept through, but they still left us manioc, squash, and chiles.

Could Ice Age civilizations have thrived without domesticating any plants? We increasingly realize that agriculture isn’t all-or-nothing, there’s a spectrum from picking wild plants when you come across them to domestication, irrigation, and the full suite of agricultural technologies. It wouldn’t surprise me if some combination of early-non-domestication-involving agriculture and hunting-gathering off of very rich lands could create enough sophistication to build a Stonehenge or a Gobekli Tepe. But you’re not getting Egypt or Great Britain off of that, sorry.

Argument 3: Lead Levels

Thanks to commenter WTFwhatthehell for bringing this one up.

Many ancient civilizations mined lead. Some of the lead made it into the atmosphere and settled down again in other places. You can measure the amount of lead in different places to see how much lead humans are mining. This isn’t perfect - the resolution is closer to continental than global - but you can check lots of different continents and get an okay reading.

This paper finds lead levels started rising 1000 BC, which it links to the Phoenician expansion happening around that time.

In theory, this could suggest that no ancient civilization reached a tech level where it started mining lead, ie the tech level the Phoenicians had in 1000 BC.

This is in theory only, because I can’t find a clear record of anyone checking. I assume ice core scientists would have noticed if it happened, but there’s no publicly available dataset with lead levels 10,000 years before present, nor is there a paper titled “We Checked To See If There Were Anthropogenic Lead Emissions In 10,000 BC And There Definitely Weren’t”.

Here is a paper that looks at lead level in human bones. They don’t do a great job explaining how lead makes it into human bones, but it seems like a mix of the kind of lead pollution that makes it to Greenland ice cores, plus personally wearing or consuming things that have touched lead. This study investigates skeletons from 12,000 BC onwards, and finds that lead levels start rising in 5,000 BC, when people developed “cupellation”, a technique for using lead to purify gold and silver (it then goes up much further between 1000 - 500 BC, probably the same spike the Greenland cores found).

So this presents some very weak evidence against significantly elevated lead from 12,000 BC onward. But it doesn’t rule out small amounts of lead mining far away from the bones’ previous owners, and doesn’t rule out a civilization lasting from 15,000 - 13,000 BC.

A Great Britain-level civilization would be expected to raise lead levels a lot, and this pretty strongly rules it out. I would expect an Egypt-level civilization to at least invent cupellation, but I don’t know if its lead would necessarily make it to wherever these bones came from. A Stonehenge or Gobekli Tepe level civilization isn’t ruled out at all.

Conclusion

I think there’s pretty strong evidence against lost Egypt- or Great Britain- level Ice Age civilizations.

I don’t want to rule out a lost Stonehenge or Gobekli Tepe level civilization, but there’s not much positive evidence, and there’s some negative evidence. Stonehenge was built by Neolithic farmer-pastoralists, who had lots of domesticated crops and animals. Gobekli Tepe was built right next to the area where wheat was domesticated at around the same time. Existing early monuments mostly suggest a story where sedentary city- and temple- building civilizations either require domesticated agriculture, or invent it very quickly.

None of this means Ice Age people didn’t have fascinating cultures of their own which were advanced in other ways - interesting laws, taboos, mythologies, customs, oral traditions. Tyler Cowen says that everything started earlier than you think, and this is what we’ve been finding about various forms of human culture too (cf. Against The Grain, The Dawn Of Everything). I just don’t expect lost Ice Age cities or giant monuments.

I think Michael Shermer’s attempt to argue the same case is weak, relies on a still-controversial rejection of the Younger Dryas Impact Hypothesis, and generally relies too much on the absurdity heuristic without moving the needle one way or the other.

All of the following predictions are about structures on Earth built by homo sapiens without time travel:

• 20% chance we ever find something demonstrating equal or greater architectural advancement to Gobekli Tepe, dating from before 11,000 BC.

• 0.5% chance we ever find something demonstrating equal or greater architectural advancement to the Great Pyramid, dating from before 11,000 BC.

• < 0.01% chance we ever find something demonstrating equal or greater architectural advancement to Buckingham Palace, dating from before 11,000 BC.