Among the British Museum’s prodigious collection of cuneiform tablets and fragments, strangely parallel experiences befell two scholars. First, in the 1870s, George Smith identified two pre-biblical accounts of a hero divinely commissioned to build an ark and so save the denizens of the world from a cosmic flood. Reading The Epic of Gilgamesh for the first time ‘after more than 2,000 years of oblivion’, he rushed around, tearing off his clothes in a state of ecstasy resembling St Francis’s embrace of his vocation. Less demonstratively, over a hundred years later in 1985, Irving Finkel was ‘more than taken aback’ when he discovered a fragment of one of the earliest versions of the flood story among bric-a-brac gathered by an English airman in Iraq during the Second World War. Finkel, like Smith, has a beard worthy of a Victorian or perhaps a biblical patriarch. His book explores even stranger parallels between Noah and the much earlier Mesopotamian ark builders.

Finkel’s find, which dates from at least 1,200 years before the earliest supposed recording of the Noah story, contains two stunning revelations for biblical studies. Astonishingly, it includes a phrase (about the animals entering the ark) plausibly translatable as ‘two by two’. So one of the striking features of the Bible story unanticipated in previously discovered Mesopotamian fragments turns out to be traceable to the same culture of origin. Moreover, Finkel’s text refers to ‘clean’ animals – and therefore, by implication, to a distinction from ‘unclean’ ones. As far as I am aware, this is the first evidence that this Jewish form of fastidiousness was prefigured in earlier foibles or scruples. Three conclusions are irresistible. First, that the flood story generated extraordinarily tenacious traditions. Second, that the tale probably originated in a world of real observation in ancient Mesopotamia, where vast, destructive floods were frequent, and not – as archaeological sensationalists have claimed – in some supposed folk memory of the effects of global warming after the Younger Dryas (or the ‘Big Freeze’, a period of cold climatic conditions some 12,000 years ago). Finally, Finkel’s tablet strengthens the already persuasive case that the Bible version derives from Mesopotamian archetypes. Finkel regards the issue as definitively resolved. Sceptics will wriggle their way round his evidence by clinging to the possibility of a fusion of Mesopotamian and Hebrew stories of independent origins; but I think reasonable critics will aver that he is right.

In the course of his investigation Finkel sheds much light on philological and literary problems of ancient Meso-potamian cultures, but one revelation dwarfs all others: in the earliest surviving description, the ark was round. The text is unambiguous on this point and includes detailed instructions for building a giant coracle out of more than 300 kilometres of coiled palm fibres, strengthening the structure with wooden ribs and decking, and coating everything in a waterproof mixture of pitch and lard. Finkel’s painstaking and lively investigation of coracle-weaving traditions on the Euphrates makes the concept intelligible. He also clears up a puzzle in the flood story that forms part of Gilgamesh, where the gods seem to ordain an obviously unwieldy square ark; a round shape, like a square, is as broad as it is long and really the Gilgamesh scribe intended a circle (or was perhaps himself deceived into squaring it). With a vivid eye for what life was like in the Euphrates valley 4,000 years and more ago, Finkel argues – riskily but plausibly – that his tablet represents a fragment from the script or record of a dramatised version of the story for court performance, and that the arithmetical precision of the calculations involved in determining the ark’s dimensions and assembling the materials for its construction derives from ancient Mesopotamian schoolroom exercises. There are other remarkable scholarly insights to admire. Finkel argues convincingly that the British Museum’s famous Babylonian world map contains an allusion to the resting place of the ark. His image of Sennacherib, the Assyrian king from 704 to 681 BC, engaged in the first hunt for relics of the foundered vessel is brilliant.

Finkel is almost as revelatory about himself as he is about the Bible text and the early history of civilisation. We see him wandering around the Study Room at the Museum, poking readers in the ribs and questioning them impishly about how he can help with their work. He complements his Victorian beard with Edwardian, or at least Wodehousian, humour. His only personal experience with boats, he assures us, occurred when he misdirected a paddle and ‘thwacked’ his sister Angela. The flood story ‘would make a corking opera’. The lions who guard the back doors of the British Museum, Finkel quips, are there to keep visitors in. He ‘could say’ that the arithmetical sections of the book, which tried his competence, relied ‘on partnership with my friend Mark Wilson but actually I just asked him a few stupid questions’. Some readers will jib, but I enjoyed most of these jolly frivolities.

Sedulous editing might have streamlined the book, which repetitions and irrelevant excursions lengthen. Prudence could be invoked to temper a few overenthusiastic speculations: there are no grounds, for instance, for excluding an intermediate alphabetical text between the cuneiform and biblical versions of the flood story, and the Old Testament’s roll call of long-lived patriarchs is not necessarily modelled on Sumerian king lists. And Finkel is, on the whole, better on the parallels between Babylon and the Bible than the differences. Two unresolved issues clamour for attention. First, Noah’s boat was glaringly different in shape and construction from Mesopotamian prototypes (though, as Finkel points out, similar in size). Finkel’s solution is to imagine Hebrew scribes consulting an unknown Sumerian version, in which the ark imitates the long reed boats of the Marsh Arabs. But every traditional, culturally transgressive story tends to get warped by updating or adaptation in successive versions. Second, the biggest difference the Hebrew version makes is to the moral framework of the myth: in Mesopotamian accounts, gods unleash the flood capriciously, or for no declared reason, or to eliminate a distractingly, irritatingly ‘noisy’ world that is becoming uncontrollably overpopulated. The Jews’ God, by contrast, acted justly, to punish evildoers and spare the only righteous man.

Noah, in other words, is a hero in a long literary transition which documents the rise of notions of a moral universe in place of a world of chaos and caprice. Early in the second millennium BC – at about the time Mesopotamian scribes arrested the development of the flood myth by writing it down as part of the court librarians’ canon – Egyptians began to paint scenes of interrogation after a moral preparation for the next life: the earliest evidence I know of a sense of a morally ordered cosmos. The jackal-headed underworld god, Anubis, supervises the weighing of the souls of the dead. In written accounts of these divine trials, the examined soul abjures sacrilege, sexual perversion and the abuse of power against the weak. Then the good deeds appear: obedience to human laws and divine will and acts of mercy, such as offerings for the gods and the ghosts, bread to the hungry, clothing to the naked ‘and a ferry for him who was marooned’. Irving Finkel has clinched the question of where Judaeans in the sixth century BC got the story of Noah. The problem that remains is where they found the moral cosmology that animates that story.