Re,
...they have all had higher flood level in earlier periods, when Co2 was not at the level it is now...





https://www.smithsonianmag.com/science-nature/evidence-for-a-flood-102813115/


And...

The Flood: Mesopotamian Archaeological Evidence

The assertion of some historians and archaeologists that a great flood devastated a region of Mesopotamia at the dawn of history and that this event was the origin of the biblical Flood story has become a curious backwater in the debate over creationism. The topic has not proved of major concern to either the advocates of recent-creationism or to their scientific opponents. It has, however, given considerable, if probably unwarranted, encouragement to day-age creationists, gap theorists, and those who hope to reconcile apparent contradictions between scripture and science.

Within a few months of one another during the 1928-1929 excavation season, archaeologists at two southern Mesopotamian sites, Ur and Kish, announced the discovery of flood deposits which they identified with the Flood described in the Hebrew scriptures and cuneiform sources. The famous and glamorous Sir Charles Leonard Woolley, after his deep excavations of the Early Dynastic royal tombs at Ur, had a small test shaft sunk into the underlying soil. He persisted through some eight feet of bare mud before finally coming to a layer bearing artifacts of late prehistoric date. It did not take Woolley long to arrive at an interpretation:

I . . . by the time I had written up my notes was quite convinced of what it all meant; but I wanted to see whether others would come to the same conclusion. So I brought up two of my staff and, after pointing out the facts, asked for their explanation. They did not know what to say. My wife came along and looked and was asked the same question, and she turned away remarking casually, "Well, of course, it's the Flood."

https://ncse.ngo/flood-mesopotamian-archaeological-evidence