Hey guys…I have a question about whether you think the following article on Wikipedia that describes the Messinian Salinity Crisis and its termination in the Zanclean Flood is valid. This refers to the drying out of and subsequent refilling of the Mediterranean Sea.
I think the last bullet point that says that the Mediterranean Sea could not have been cut off from the Atlantic Ocean during the last Ice Age is an unjustified conclusion, and I present a counterexample to show this:
First of all, the claim that the Strait of Gibraltar is today, at its deepest point, 900m below present-day sea level is entirely true. But the claim that given that the sea level was 120m lower during the last Ice Age, the Strait of Gibraltar would still be below the waterline (900m - 120m) by 780m at its deepest point during the Ice Age is, while seemingly a perfectly rational conclusion, in actuality contains a subtle assumption.
Here’s the counterexample:
Imagine that the Strait of Gibraltar was 10m above the sea level 20,000 years ago, and that it was an isthmus which was rather narrow, and further, that this above-sea level isthmus had remained above the sea level for a time period of greater than 1,000 years, which is the amount of time that is estimated to be needed to dry out the Mediterranean Sea into a basin given that it is blocked from the Atlantic Ocean.
Then the Mediterranean Sea would, at the time of 20,000 years ago, be a dry basin; further, not merely just reduced some 120m below its present level, but reduced either completely down to its deepest basins, or some amount far greater than just 120m; perhaps 2 km.
We know that the Mediterranean region near the Strait of Gibraltar, is, today, a very tectonically active region. The 1755 earthquake offshore of Lisbon Portugal, which had a moment magnitude of around 8.7, is an example of how large earthquakes close to magnitude 9 can happen near that region.
Because the Mediterranean Sea would be a basin in that situation, it would be supporting the entire mass of the ocean water on its west side (the Atlantic Ocean), and only air on its east side (because the water had dried out in the Mediterranean). Even given the increased atmospheric density on the right side due to the greater depths in the Mediterranean basin, the mass of water on the left hand side would still have a density of some 500 times greater than the air on the right hand side, and a pressure even greater.
So you have a disequlibrium of forces, since pressure is force over area, and the area exposed on both sides of the isthmus underwater are probably reasonably similar, yet a static situation. If this net force exerted on the isthmus’ exceeds the breaking strength of the isthmus, and the breakage that results either occurs below the water surface, reduces the height of the isthmus above the then sea level from 10m above to something even like -5m above, the Atlantic Ocean will spill over that reduced height isthmus.
Let us assume that given such an disequilibrium of forces, an earthquake on the scale of the 1755 Lisbon quake (8.7 magnitude estimate), could potentially be a trigger event that reduces the tensile/breaking stress of the rock that makes up the isthmus so that the net force exerted on the isthmus, which was prior to the quake, insufficient to exceed the breaking stress of the isthmus, but now exceeds the breaking stress; not because the net force on the isthmus (i.e. the level of the ocean in the Atlantic increased, but because the earthquake caused the breaking stress of the isthmus rock to decrease…so that the unchanged net force suddenly “found itself” above the decreased breaking stress.
Then, the Atlantic Ocean would intrude into the Mediterranean basin. Perhaps even at a trickle at first, but scientists who worked on the Mediterranean Sea flood and studied the one 5.33 million years ago have done geophysical modeling that showed that a trickle would soon grow into a torrent.
This torrent would flow at a tremendous speed, which I argue would be sufficient to carve down what was prior to the earthquake+breakthrough of Atlantic water an isthmus into a deep U-shaped canyon. Since the sea levels 20,000 years ago were 120m below present day sea level and the hypothetical isthmus above-water I supposed was 10m above the then sea level of 120m, the isthmus would originally have been located at 110m (-120m + 10m) below present-day sea level, yet still NOT underwater (that’s my supposition). The earthquake+incursion of water would then erode a total vertical distance of (-110m - (-900m)) = 790m, so that we now look at the present-day vertical maximum depth of the Strait of Gibraltar and say the water level never went down to 900m below present, so the Mediterranean couldn’t have been cut off…but what if in actuality, the reason the strait is so deep today was because it did dry out 20,000 years ago as H.G. Wells hypothesized, and the ensuing flood that refilled it actually carved what was an isthmus 10m or so above the sea level of -120m all the way down to the present depth of -900 m (a total of 790m)?
Do you think this is a valid counterexample to the widely-held conclusion that the Mediterranean Sea could not have dried out during the last Ice Age?
The question is, does the current sea-floor topology of the strait, extending below the level of the last ice age level, look like it could have formed due to erosion during a refill event? And thus the blockage/isthmus could have been above sea level prior to that? How high are the “shoulders” of the submerged valley? If it had not been cut, could we assume the blockage would have been above ancient sea level?
Not sure where you find answers to this. SOmeone must have a depth map.
Of course, this was not the first ice age either, so perhaps the answer lies 100,000 years or more ago?
My point is that one cannot use the present depth maps to say conclusively what could have or could not have happened in the past, as the present depths and past depths are not necessarily the same, and it is the past depths, whatever they may have been, that we must use to say what could have or couldn’t have occurred (i.e. an isolation and hence drying, and then subsequently a reflooding).
But we don’t know what those past depths are, at least not simply by looking at the present depths. It’s a question whose answer is to be found not by simply looking at data that is collected about present-day depths. Present-day depths are the first step in the journey of a thousand steps, but I feel as if many take them to be the journey itself that concludes the debate when it could possibly be just that - a single step in the whole journey, the journey being the full understanding and reconstruction of what happened with the Mediterranean, and when.
I believe that it is possible to falsify a flooding of the Mediterranean Sea between 20,000 and 10,000 years ago, or sometime in the last 500,000 years, but that it must be done through looking at multiple evidence and data sources, one of them including dating the most recent salt deposits, and not by looking at the depth readings alone.
If the most recent salt deposit on the seabed was 5.3 million years ago, and this data is corroborated by multiple sources, I think the issue is settled beyond debate.
This brings up the key point, and the answer to this question is a resounding no. If it had not been cut, then we would know that there wouldn’t be a blockage/it would be below sea level.
So the statement, “if it had not been cut, then we can conclude that the strait would have been below sea level” is a true statement.
But, likewise, the statement (which is a converse of the previous statement), “if it was cut, then we cannot concludethat the strait would have been below sea level,” is (and that is my claim) also a true statement.
So for the former hypothesis, namely the one in which “it had not been cut” is a true clause, the conclusion is definitive. We can know for sure that the strait would have been below sea level. But for the latter hypothesis, in which “it was cut” is a true clause, the conclusion is indeterminate. Namely, we cannot conclude that the strait would have been below sea level, but we cannot conclude the negation (that it would have been above) either.
Summarizing the above, the statement that “if it had not been cut, then we can conclude that the strait would have been below sea level” is true. It is also true that (being the contrapositive of the latter conditional statement) if we can conclude that the strait would have been below sea level, then it was not cut.
Labeling the two clauses:
A := it had not been cut
B := we can conclude that the strait would have been below sea level
C := it was not cut
my paragraph above reads as:
Summarizing the above, the statement that “if A, then B” is true. It is also true that (being the contrapositive of the latter conditional statement) if B, then C.
By the “transitive property,” we have that the statement “if A then C” is also true, since “if A, then B,” and “if B then C” are both true. So “If it had not been cut, then it was not cut” is a true statement (resubstituting the clauses). Since we have reduced the totality of all statements (the first one and its converse namely) into an identity, we know that what has been said so far is in fact true. (It would only be circular if the statement “If it had not been cut, then it was not cut” was assumed, rather than proven.
I think I have also proven that this doesn’t really matter, and that I don’t have a life. But that’s circular reasoning.
Meh, I guess I just find it a fascinating thing that things have happened on this Earth that are so powerfully destructive and catastrophic. It’s a perfect example of “truth being stranger than fiction,” meaning the flood that did happen 5.33 million years ago.
If I understand your (long) post correctly, you’re suggesting that the fact that the channel is so deep now is irrelevant, because if it was shallow enough 20,000 years ago to cut off the Mediterranean basin from the Atlantic, the subsequent flooding event when sea levels rose would be powerful enough to carve the very deep channel we see today. I agree that if the situation you described did in fact play out, it would indeed very likely result in a very deep channel.
However, you seem to believe that we have no way of knowing how deep the channel was tens of thousands of years ago: “But, likewise, the statement (which is a converse of the previous statement), “if it was cut, then we cannot concludethat the strait would have been below sea level,” is (and that is my claim) also a true statement..” Here is where you are wrong. The sediment record allows us to know with some precision what the bathymetry was like in the past. Whether the current channel was cut 1 million years ago or 10,000 years ago is easily determined by studying the stratigraphy of the Strait.
If Well’s theory was correct, and as you suggest the current deep channel was carved out only 20,000 years ago, it would almost literally jump out to the first person who took sediment cores in a transect across the Strait.
Regarding your first paragraph, yeah, that captures it perfectly. On your second paragraph, I have considered it and believe it to be very much reasonable save for one exceptional case. (As a side note, I believe the main evidence for a drying out/flooding is based on the content of the sediments; salt beds mainly, I’m guessing you mean this by stratigraphy.) What I will try to argue is that each subsequent layer in the stratigraphy (i.e. salt beds), will be added on during a dessication/isolation/reflooding event only if during that event precipitation of dissolved salts occurs; in other words, sedimentation requires precipitation; and I will demonstrate that there is a counterexample, namely that there could, in certain climatic conditions, be a isolation/dessication/reflooding event in which precipitation does not occur at all, or in minuscule amounts that are statistically insignificant and hence potentially “missed,” and thus sedimentation does not occur and hence is not observed in the stratigraphic record (no sedimentation, no stratigraphic record for us to detect even though the dessication/isolation/reflooding event actually happened.)
Here goes: (sorry, it was late at night and my mind was muddled and I probably went into a “stream of consciousness,” rather than the clearest, concisest statements. But I think the content, although long, is logically sound - I promise it won’t be a cop-out, rationalization, but a legitimate attempt at a spirited debate on a very good point that you made (that requires a lengthy response to address adequately).
The time period in which H.G. Wells claimed this event to have occurred was 10-20,000 years ago, when Europe, as was North America, was covered with enormous ice sheets. Almost all of the British Isles, North Germany, and all of Poland were covered in a continuous continental ice sheet; also, the Pyrenees range between France and Spain, and the Alps in Northern Italy and neighboring nations were covered with mountain glaciers about the size of the ice cap that covers Iceland today.
In North America, the glacial conditions and the Laurentide Ice Sheet, which reached down to Wisconsin, led to a dramatically altered climate. Of course, it was much colder. But a rather interesting phenomena that we know of is that in regions such as present-day Utah and the Great Basin states in the Western United States, there were these giant pluvial lakes that dotted the terrain. Now it might be surprising, but these pluvial lakes did not exist mainly because of the meltwater from the ice sheets. They existed because of increased precipitation in regions south of the ice sheet combined with a reduced evaporation rate (due to the colder climate). From Wikipedia:
Why is this information relevant? Because the decreased evaporation rate and increased precipitation rate would, if the former was not decreased so much and the latter increased so much so that the Mediterranean Sea would simply not dry out even if landlocked from the Atlantic, still lead to a substantial reduction in the level of the Mediterranean that was much greater than the 120m drop worldwide (say something like 2 km from the average of 4 km), but not the entire sea all the way down to its bed, or at least not so much that the concentration of NaCl would exceed its solubility limit.
The solubility limit of NaCl in water is remarkably stable with changes in water temperature, and is around 360 g/kg water just above freezing point and just below 400 g/kg water just below boiling point, with temperatures anywhere in between these extremes having intermediate solubilities. At “room temperature,” it is around 370 g/kg water.
The present-day total salt concentration of the Mediterranean Sea is, being just slightly above the world average, around 35 g/kg water; since Na and Cl contribute over 85% to the total salt concentration, assume that the other dissolves species are negligible, and that there are 35 g NaCl/1 kg water in the Mediterranean Sea.
If the Mediterranean Sea was drawn down by a significant amount, but with a final “equilibrium” level that corresponded to a water volume greater than a tenth of its present volume, the concentration of NaCl in it would increase, but would increase to less than the solubility limit of 360 g NaCl/kg water.. Since precipitation of NaCl only happens when its concentration exceeds its solubility limit, if it were the case that the Mediterranean Sea dried out even 7/8 or 9/10 of its volume, and thus remained at a concentration below the solubility limit, no NaCl precipitate would occur whatsoever.
But given the fact that we know that 20-10,000 years ago, the climate was different (much cooler and wetter in the Mediterranean region, most likely), from both the 5.33 million years ago time period and today, and further, given the fact that we know that pluvial lakes formed in latitudes similar to the Mediterranean whereas today they are very salty lakes that ended up completely drying out and thus depositing their salt content in salt flats all over the Great Basin/Utah area also a similar distance southward of a continental glacier, isn’t it possible that a hypothetically landlocked Mediterranean Basin would also lead to a drawdown in water level, if a drawdown did indeed occur (instead of no change or even an increase in the water level) that would be insufficient to lead to precipitation of the salts?
In my view, such a supposition is plausible, although certainly not definitive. In the paragraph above, I tried to explain how it could have been plausible that the water levels in the landlocked Mediterranean sea/basin under ice age conditions could specifically have not completely dropped, or not have dropped enough for deposits of precipitate to form. But what if under the ice age conditions, the water levels dropped only some 100m, or even perhaps rose by 100m or 200m? The possibility of the water level rising in the landlocked Mediterranean “Sea,” cannot be excluded - after all, if there were pluvial lakes forming in N. America, there was a lot of precipitation and runoff, and less evaporation; couldn’t that possibly lead to an increase and overflowing of the Mediterranean basin the other way around - either into the Atlantic or onto the Sahara Desert, if it existed at that time?
I think this is rather unreasonable because of the following reason: The pluvial lake Lake Bonneville, which now has a remnant called the Great Salt Lake, had a mean depth of about 800 feet. [Lake Bonneville - Grove Karl Gilbert - Google Books](Geology textbook documenting this average depth). The Mediterranean, on the other hand, has an average depth, today, of 4900 feet. If it is a reasonable analogy that the evaporation-precipitation/runoff ratios were similar in Lake Bonneville and the Mediterranean landlocked sea, by virtue of their similar climates (this was shown to be reasonable in previous paragraphs), then it wouldn’t be a bad starting “educated” guess to suppose that the Mediterranean Sea would have dropped down to around 800 feet if landlocked.
But 800 is only slightly less than a sixth of 4900. Even assuming that the Mediterranean Basin is shaped more like an inverted frustum wider at the higher regions and narrower at the lower, rather than a region with uniform “cross-section areas” at all heights in the basin, there is still room for a possibility that the 800 feet of water so left would then have a salinity of more than 6 times greater than present, but less than 10 times greater, which is the amount that would trigger precipitation. And this incidentally also shows why it’s reasonable that the Mediterranean did not either drop only trivially, or actually rose - if Lake Bonneville could only support a lake 800 feet in depth, then for the Mediterranean to support a lake/sea 5 or so times deeper, in the range of 4000 feet deep on average, is unlikely (and even at such a “small” reduction in water level, that would still be 900 or so feet, which is not really that small; but the point is that the reduction, if analogies to Lake Bonneville are not off by a lot, is not at all implausible to have been much greater than by a factor of 2 (i.e around a factor of 6), yet also quite possibly not greater than a factor of 10. And if it is a stretch to say that it could have decreased only by 900 feet, then it is even more of a stretch to say it would have decreased by only 30 feet, stayed the same as the global mean sea level 10-20,000 years ago of 400 feet below…when I mention decreases previously, I mean decreases relative to the global mean sea level 10-20,000 years ago (400 feet), and NOT relative to present global mean sea levels, or have increased (so that the water level of the Mediterranean landlocked sea actually exceeded that of the 10-20,000 years ago Atlantic Ocean level).
And if it was indeed the case that the Mediterranean dropped (which was shown to be quite plausible), by a factor less than 10 in volume, and remained so for the entirety of its existence as a landlocked basin, then its concentration would have remained less than 10 times greater than it is now throughout that entire time. If so, then at no time during that interval would any sodium chloride deposit/precipitate in sediment to form what we can collect as data that we use to conclude that there was a drying event.
While it is positively true that deposition of thick salt sediments is sufficient to prove near complete evaporation of a landlocked basin, I have presented the above lines of reasoning to argue that, to the contrary, the lack of deposition of large beds of salt/sediments does not exclude the possibility of a drawdown in sea volume by a factor of even up to any factor less than around 10 - for in such a case, no precipitate would be deposited for us to record as data, with the result that given our present data collection techniques could be giving us a “false negative.”
And when the hypothetical land bridge broke, as H.G. Wells thought, the seawater entering from the Atlantic Ocean would be not too much different from what it is today (it would be slightly greater, given the lower levels, but 120m is not that much compared to the 4000m average for the world oceans) would mix with the water in the Mediterranean basin, which would be more concentrated by a factor of 6-10 (I showed why this is plausible); thus, the Mediterranean basin remnant “sea,” in the flood, would be diluted back to, eventually, to an equilibrium salinity just above the world ocean average as it reconnected with it. The key point is that this whole sequence of events I have hypothetically constructed is consistent with H.G. Wells’ hypothesis, and from the landlocked state, to the drawdown from 4900 to around 800 feet (of 4100 feet, almost), and to the dilution from flooding, the salinity could remain below the 350 g Nacl/1 kg water needed for precipitate to occur (and during the refilling itself, as was shown, the salinity wouldn’t increase from its landlocked state, it would inevitably decrease, thus rapidly eliminating “for good,” and possibility of precipitate to a probability of zero).
In other words, an entire landlocking, 4,000 feet or so drop in Mediterranean water levels, and a catastrophic refilling (which you have said was plausible as I’d described in my previous post tectonically speaking, although extremely unlikely since there would be copious or at least detectable sediment deposits i.e. salt, halite) with essentially no trace left behind in sedimentation; with the lack of fossilized dead marine life (if there is indeed such a lack) being explained by the fact that the salinity maybe didn’t increase by enough to kill marine creatures (although this is less convincing I believe, since a salinity rise by a factor of 6 or so, while insufficient to cause precipitation, might be too hypersaline for fish to live).
On the flip-side, they could have barely eked out a living, and not died en masse, but had a lower population size and reproductive level so that even though many more of them died per 1000 members of a marine species, there were less total members so that the total number of fossils/trace of animals dead remains roughly similar an undetectable. In other words, maybe even a time of hypersaline conditions and enormous stress on marine animals could have remained, in terms of the number of dead creatures on the bottom of the sea being recorded, not very much increased due to the lower population sizes during that period “across the board” of animals.
If all of these extremely unlikely, independently, conditions are met, the Mediterranean Sea could have been captured in its historical evolution over the last 20,000 years (or more recently than 5.33 million; i.e. during the last ice age period after 100,000 years ago), almost exactly as H.G. Wells said (in my humble opinion).
Of course, if even one key condition of the probably 4-5 or so are not met that I have mentioned both in this post and in my previous one to which you replied earlier, then it’s clear and unambiguous that there was no such flood. But I believe I have demonstrated that there could have been such a flood in the last 10-20,000 years, with a small but not negligible probability that if it did occur, then the sediment evidence we are looking for could be almost entirely not present, even though it actually happened! If it did indeed happen, then the flood would be somewhat of a “perfect crime” that left “no trace,” even though it was so enormous in its extent. After all…we do know that the Mediterranean did dry up and refill not just once, but even in cycles prior to 5.33 million years ago. The question is, has the serial killer struck again, in a time when Man was, anatomically and behaviorally speaking, essentially “fully modern?” :dubious:
Ha, I have to say, I’m getting a kick out of your posts. You certainly go to great lengths to explain yourself! However…
Bolding mine. You guessed wrong. When I mentioned sedimentology/stratigraphy with respect to dating the channel, I wasn’t talking about the presence of salt beds. I was talking about the fact that by analyzing sediment and rock cores taken in the channel of the Strait, we can determine how long ago the channel in the Strait was carved. This type of analysis has nothing to do with the presence or absence of evaporite minerals, but rather looks at the size, distribution, and composition of the different layers found in sediments to determine when it was laid down. Basically, if the channel was carved recently (~10-20,000 years ago), when you take a core of the bottom you’d see 20,000 years of “new” sediment layers lying directly on top of very old layers, the intervening sediments having been washed away during the flooding event. Suffice it to say, scientists can tell A LOT more from looking at a core than you probably think they can. It’s not just looking at layers like the rings of a tree. For instance, stable isotope analysis can allow them to determine when a certain layer was formed, and even the average water temperature when it was laid down. It’s a very refined and reasonably precise science.
Since I wasn’t talking about salt/evaporite mineral deposition the rest of your post doesn’t really have anything to do with mine. Although I certainly agree with you that it’s hypothetically possible for the Med. Sea to significantly decrease in depth without actually reaching the point where evaporite minerals form, I’m trying to point out that if the Strait of Gibraltar used to be much “higher” than it currently is, only to be rapidly worn down to it’s current bathymetry by a massive flood 20,000 years ago, that would be readily apparent to scientists today by studying the layers of sediment at the bottom of the Straight.
Incidentally, one of the first pieces of evidence for the Messinian salinity crisis was found when they were taking sediment cores in and around the Nile River in preparation for building the Aswan High Dam. They discovered that near the river, they had to go down about 1,000 feet to hit bedrock, but on either side the bedrock was almost at the surface, say 100 feet or so. This implied that at some point in the past, the Nile river carved a canyon in the bedrock that was almost 1,000 feet below sea level as far upstream as Aswan. It was later determined that this canyon was carved when the Med. basin was dry, and the Nile ended in an enormous waterfall that poured into the basin. Gradually, the waterfall worked it’s way all the way back to Aswan (and even further) before sea level rose enough to flood the canyon. This a great example of strong stratigraphic evidence of the Messinian event that doesn’t have anything to do with salt or gypsum deposits.
I agree with your point on the deposits, and I clearly haven’t read enough about the mission that collected the samples or stratigraphy. I’ll go read up on that sometime this week.
