In fact the oceans have been subjected to the same sort of massive upheavals and tortured history as we have seen overtook the lands. In some ways the changes have been greater, as they have altered the very nature and composition of the seas.
The Extent of the Oceans
Only around 30% of the Earth's surface is land, and of this land probably a good deal less than 30% does not show clear signs of marine inundation of some sort in the past. So no more than 10%, and possibly very much less, of the current land surface has escaped a period under the waves.The average depth of the oceans [37] is around 3.5 km, and the average height of the land above sea-level is only about 750 m. The deepest spot in the oceans is believed to be in the Marianas Trench, off the Philippines, with a depth of 11 km (more than the highest mountain, at 9 km).
How does this situation fit in with the aspect of Expanding-Earth domains, and in particular, what is known or believed in regard to changes in sea-level? This turns out to be a complex question, with a number of forces active, some in opposition and some acting together.
To clear the field a bit, it must first be reiterated that all measurements and deductions of where the sea reached on different pieces of terrain in the past, and former comparative sea-levels in different parts of the world, are close to worthless. In the image of jostling, moving, and rising and falling domains and microdomains which we have arrived at (Fig. 9.2), the unqualified comparison of the present heights above sea-level of two distant points on the Earth is meaningless.
So also is a deduction that the sea has risen or fallen generally, working from the present position of a point in relation to local sea-level. As an example, a recent drilling program for a gas production platform off the Northwest Shelf of Western Australia showed that seabed strata 125 m below the sea-bottom (itself over 100 m down) had been dry land in geologically recent times, and yet were sandwiched between strata believed deposited in water deeper than 100 m.
The normal inference from this information would be that the sea had retreated at least 225 m in the past at the time the dry-land formation was created. While this is quite possible, it is equally possible that that portion of the seabed was on a domain which had risen and fallen by this distance, relative to a sea of unchanged level.
Proposition 10A
Most observations and deductions on the position of sea-level
relative to particular points on land today are meaningless when
applied to general sea-levels in the past
This Proposition (or at least the reasoning behind it) is already accepted in detail, if not in large. Measurements and calculations are often produced and accepted which claim that Continent A is rising relative to Continent B by several millimetres each year, and so on. One millimetre per year is one metre in a thousand years, or 1 km/ my, so that a tiny change of this sort continued on for what is a short time by the standards we have been using -- less than the existence of the human race -- would be ample to sink all current landmasses beneath the sea and raise new ones.
And yet, maps are still being drawn for geological textbooks, showing the position of the sea in Carboniferous times, 300 million years ago!
Volume of the Sea and Earth Expansion
Whether on the conventional view or using the outlook explained in this suit of articles, it does, in reality, appear that land areas in the past were by and large the same bits of real estate as the land areas now. The domains involved may have sunk or risen relative to the local sea-levels, or vice versa, but virtually all the deep ocean beds are less than 200 my old. We have seen the reason for this -- these seabed areas did not exist in any form on the pre-expanded Earth -- but this still leaves us with a problem. Why wasn't the entire globe underwater in earlier times?Suppose that, at the beginning of Devonian times, 400 my ago, the Earth had half its present radius. Its surface area would be a quarter of that now. If the water in the present oceans was spread uniformly over the present Earth, it would form a layer about 2.5 km thick. On the Devonian Earth, the same water would be 10 km thick. If the Earth had the similar landforms to now, except that all the present land areas were pushed together to cover a half-radius Earth, not even the tallest mountain would be above the surface.
The first life on land, both plant and animal, appears to have emerged around the Devonian, so real land areas clearly existed then. What is the explanation of this paradox?
The simple answer is that there was much less seawater on the Earth in Devonian times. This leaves us with another problem, explaining where the 'new' water has come from, but that is another issue. For the moment we should accept this explanation.
Proposition 10B
In earlier ages the Earth had a smaller total volume of water
on its surface
This is not to say that the total land area was any greater in those days, in fact the converse is probably true. Although life appeared in profusion some 600 my ago, its earliest records date back 3500 my -- microbial lifeforms found in the rocks of northern Western Australia. Of course all these early forms of life were water-living creatures; it is only when we reach the comparatively short time of 400 my ago that the first land creatures appear.
Why did it take so long? We have seen that lifeforms evolve really quite rapidly, with major changes occurring during a few million years. The vast majority of extant lifeforms, and their immediate and more distant ancestors, have all evolved during the Tertiary Era, the last 70 my. Why was there no life on land till the Devonian, while 200 my of intense evolution had just taken place in the sea?
The answer to this, I believe, is that land itself only appeared around the Devonian. Before this, the Earth had not expanded enough to expose more than perhaps a few peaks through the surface of whatever seas existed at that time.
Proposition 10C
The first substantial land appeared above the sea around 400
million years ago
The scenario is thus of an expanding but much smaller Earth, with less water distributed over its surface, but sufficient to cover irregularities in the surface almost completely until the highest of these were exposed in the Devonian -- the Earth having already reached more than 90% of its present age.
This scenario is consistent with the fact that marine sedimentary rocks exist over so much of the present land.
Where Has the Water Come From?
To return to the matter of where so much of the present ocean water has come from, and to highlight a related point. Way back in NU005, the suggestion was made (Proposition 5M) that in making pre-expanded Earth constructions, domain boundaries should be taken as the present sea-level boundaries, ignoring continental shelves.This proposition still holds, and will be further supported by more evidence later, but it will now be clear that this proposition does not imply that domains with current sea-level boundaries had sea-level boundaries in those older periods. Nevertheless, there has been a very approximate preservation of land areas since the Devonian, implying some continuing source of new water since then to at least partly keeps the oceans 'topped up' as their basins expanded away under them.
The problem of explaining where the present ocean water came from is heightened by the fact that, as we shall see in the next article, the Earth has lost very considerable amounts of water into space.
The only credible source for this water would be one which tended to keep pace with the expansion process. I believe that this source derives from the expansion process itself.
The point is that Earth expansion continually exposes new rock to the surface, or at least takes it into the lithosphere where domain churning lets it be worked on. Although not obvious, it seems quite probable that this rock contained some water. The fact that volcanos give out steam, as well as other gases, is well known. In analysis of rocks, any water present is usually assumed to have come from groundwater, or from the sea in the case of seabed cores, and the water is often not taken into account as a rock component.
Proposition 10D
Water is being added to the Earth's hydrosphere from internal
materials brought into the active domain zone by Earth expansion
This proposition is a reasonable explanation of the position, since the volume of rock brought into play will be proportional to the new surface area created by expansion, thus releasing enough 'new' water to keep pace, partly at least, with the new ocean volume. Any other explanation unconnected with expansion -- such as the Earth gathering hydrogen from interplanetary space during its passage (which is still a distinct possibility) would not have this important proportional feature.
Also, from the cosmological viewpoint, hydrogen is the most common element in the universe, and oxygen is the most common element on Earth. Water is a compound of these two elements, and however the Earth was formed, it seems reasonable that a significant proportion of these two elements should exist right throughout the Earth's substance.
Is the amount of 'new' water generated enough to keep the oceans fully topped up? I suggest that it is not, and this causes a continuing small fall in average sea-levels, with the result that the total land area of the Earth is increasing. Let us try and put some figures to this.
The Level of the Seas
For the moment we will only be concerned with long-term change in sea-level which stem from Earth expansion, and will not think about short-term or local effects due to ice ages, Greenhouse effects, or domain jostling.According to the latest figures [18], the current rate of increase of the Earth's radius is around 3 cm/yr. If there was no 'new' water coming in from below, we would expect the average sea-level to be dropping because of this each year.
The actual amount is quite hard to calculate (it needs to make assumptions on the average rate of slope of the solid surface over all the Earth's seashores and seabeds, and the places where the actual expansion shows up), but it looks to work out at only around one-thousandth of a centimetre per year (I am open to correction on this). This is equivalent to a drop of 1 metre in 100,000 years, or 10 m/ my, and clearly can have no short-term effect.
Even so, on the longer term this figure looks to be of the right order. The drop in sea-level since the Devonian, 400 my ago, would be 4000 m or 4 km -- about half the 7.5 km difference between the current 2.5 km thick layer and the 10 km layer which would have existed if the same water had been present on a half-radius Earth.
Proposition 10E
The average annual fall in mean world sea-level as a result
of Earth expansion is of the order of one hundredth
of a millimetre per year
In the next article, NU011, evidence will be brought forward supporting the suggestion that Earth has also lost a huge amount of water into space. As a very approximate first stab, let us assume that the other half of the 7.5 km drop in sea-level is due to this mechanism, which thus produces a similar rate of fall.
Proposition 10F
The average annual fall in mean world sea-level as a result of loss of water to space is also of the order of a hundredth of a millimetre per year
Both these figures are admittedly open to considerable adjustment and correction from a more detailed approach to the calculations involved -- since all the mechanisms involved have only now been put forward in a broad context, with even the existence of such figures perhaps suggested for the first time, it is a bit rash to put numbers to them. Where angels fear to tread ....?
Early Man and Shorter-term Sea-Level Changes
It is currently believed that the earliest creatures which might be regarded as the direct ancestors of modern man existed some five million years ago. These were not men in the modern sense, but were a distinct branch of the higher primates -- about as different from the other apes as chimpanzees are from gorillas.True men have probably existed for much less than a million years, with the beginnings of civilization no more than 20,000 years in the past. Our knowledge of the evolution of man is sparse -- only relatively isolated remains have been found, really quite a small number of 'missing links' between the apes and man.
Against this 5 my background, perhaps the most important physical events have been the Ice Ages. These were times when the polar icecaps apparently covered much larger areas than now (however, see proposition 7H), and there were a number of cycles of advancement and retreat. The oldest was around 110,000 years ago. The most recent was only about 10,000 years ago (we may be in the middle of a cycle now), so the Times of Ice were well known to man, perhaps even civilized man.
These Ice Ages are claimed to have had huge effects on sea-levels, at times amounting to hundreds of metres, through the locking-up of water in the great icecaps. As an example, evidence has been put forward for the existence of a huge freshwater lake, dubbed Lake Carpentaria, in what is now the Gulf of Carpentaria (Fig. 10.1). The lake existed between 26,000 and 10,000 years ago, caused by a drop in sea-level due to polar ice accumulation of 150 m [30].
Fig. 10.1. Former 'Lake Carpentaria' between Australia and New Guinea
One item of supporting evidence is that the same species of freshwater frogs and turtles exist both in the Arnhem Land area of the Northern Territory and in Papua New Guinea and West Irian to the north. These are presumed to have dispersed through the lake.
The Aquatic Ape and the Missing Link
Marked falls in sea-level in the period of man's evolution have an interesting implication. In 1982 Elaine Morgan published a book, 'The Aquatic Ape', containing a great deal of persuasive evidence suggesting that man had been through a partly aquatic phase in his evolution. This book was based on a proposition put forward by the British marine biologist, Sir Alister Hardy, in 1962. It is not possible to summarize a whole book in a couple of paragraphs here, but the evidence seems undeniable that man differs fundamentally from the other higher primates in ways which suggest a much higher degree of linkage to a water-dependent existence.Physically, humans are notable for such things as hairlessness, deposits of fat under the skin, prominent mammaries in the female, 'flow lines' in remaining hair deposits, and tendency to webbing between the toes (up to 7% of the population). All these are features which are common to aquatic mammals but are completely lacking in the other land apes.
Psychologically, the love of mankind for water (swimming, sailing, and surfing are regarded as very pleasurable by many) and the tendency for towns and cities to be built on the edge of water are well known, again in contrast to the other apes, which generally have a strong dislike of water.
On the other hand, some non-primate mammals such as elephants and pigs possess many of these 'aquatic' features and are also believed to have had an aquatic phase in their evolution. Both are strong swimmers, elephants having been known to swim distances as far as 500 km in the sea, of their own volition. It is not suggested that man was ever a completely water-adapted mammal, like the whale, only that during his evolution at least part of the race became adapted to very regular use of water and so brought in these 'aquatic' genes.
Here then is a possible explanation for the comparative dearth of hard fossil evidence of man's evolution. If much of this evolution took place in the shallow waters, or at least on the sea's edge, and water levels have since risen generally, they would conceal much of this fossil evidence.
Proposition 10G
Much of man's evolution took place in a semi-aquatic environment,
and rising sea-levels have concealed most of the fossil
evidence for this evolution
Of course it is possible to try and verify this proposition. It seems highly likely that human evolution was especially active around the African and Asian shores of the Indian Ocean. It should be possible to select likely sites for underwater archaeology -- the Red Sea and areas near river mouths in East Africa are possibilities -- to try and recover such remains.
There is a further implication. Back in NU006, I noted the apparent close genetic links between the Pygmies of Africa and the Negrito people of the Philippines, and pointed out that the elapsed time was insufficient for these two groups to have evolved together and been later separated by Earth expansion. In Proposition 6D of the same article I suggested that the isocons for marine seashore creatures were thin and long -- creatures could spread rapidly along the shores, but not over them into the land or the sea depths.
Putting these two together we have the possibility that early man lived mostly in the long, thin shallow-marine isocons and not in the squarer land isocons of most land animals. This does provide some sort of explanation for the Pygmy-Negrito puzzle.
The 'Land Bridges' of the Past
The short-term tying-up of large amounts of water in polar ice caps must inevitably lead to falls in average sea-levels. But we know that this is not the only mechanism affecting sea-levels, nor will sea-level changes necessarily be uniform over the whole globe.There has been a tendency to find evidence that two areas of land now separated by sea were once linked, and assume that this was through a 'land bridge' between them. This then leads to the assumption that the sea had retreated generally, enough to expose the seabed to at least the depth needed to form a continuous land link, and the depths needed have sometimes been very large. Even between Rottnest and the mainland, this reasoning has been used to suggest that the sea must have receded the 24 m needed to expose a land bridge between these points in the comparatively recent past.
We can see now that this reasoning may be defective in two ways. Firstly, two currently separated domains may have been moved apart by normal domain movement, so that there was never an actual 'land bridge' between them which has since been inundated. Secondly, specific relative movements of sea-level may have been purely local phenomena due to domain shuffling, rather than general movements of sea-level.
Proposition 10H
Geological and biological evidence explained in the past by
hypothesized land bridges may be more readily explicable
through domain movements
Again this is a proposition where the implications are already accepted in detail, if not in large. Relative rises and falls of two continents of the order of 1 cm/yr have been calculated and accepted generally in the past. This is equivalent to a change of 1 metre in 100 years or 1 km in 100,000 years, the period of active modern human evolution. Changes of this order through domain movements can clearly explain many observed variations in apparent sea-level.
The Salty Sea
Of the more than 200 islands larger than 10 ha which lie off the coast of Western Australia, Rottnest is unique in possessing a salt-lake complex [70]. In fact the salt-lake system dominates the eastern half of the island, and in total occupies 229 ha, more than 10% of Rottnest's 1900 ha.Most of these lakes are exceedingly salty, up to seven times as salty as seawater in the dry season, and in one area a 2 ha salt-pan dries out each year, leaving thick deposits of salt. Collecting salt from the Rottnest salt-pan was one of Western Australia's earliest industries, and very large quantities were taken out in the past, as much as 1016 tonnes in a single year [75].
One of the mysteries of Rottnest is where all this salt comes from. It has been suggested that it is washed out of the atmosphere -- surprisingly large amounts of salt are contained in rain, even that falling well inland (1000 mm of rain deposits about 500 Kg/ha of salt on the West Australian coastal town of Geraldton, and over 170 Kg/ha on Coolgardie, more than 500 km inland). Another possibility is that seawater percolates through the porous Rottnest limestone into the lakes (which are below sea-level) and there evaporates.
There is a lot of salt in seawater -- on average about 3.5% is dissolved solids, of which the majority (85%) is common salt, sodium chloride. In the open seas, the proportion varies both with latitude and proximity to land and river mouths, and with depth. Where does this salt come from and was there always so much of it?
The Ancient Seas
It seems a reasonable assumption that the source of the salt is the Earth's rocks -- clearly most of the solid matter on Earth originates there, and even, as we have seen, at least some of the water. This salt circulates throughout the biosphere, coming from the sea onto the lands with wind and rain and returning through the rivers and underground aquifers.As well as this rapid turnover, there is a much longer-term cycle in which salt is deposited in beds from continuing evaporation of water, and eventually converted into rock salt. Some rock salt beds are of great thickness, up to 400 m. Salt deposits are in the process of formation today, and have been formed in rocks of varying ages stretching back at least as far as the Permian, some 300 my ago. Before this they are not known with certainty.
There are grounds for believing that the salinity of the ancient seas was much less than that of today. The evidence is indirect, but reasonable. One interesting item concerns the composition of blood.
When creatures evolve to suit a change in their ecological conditions, when they cross the isocons, some of their characteristics are altered to suit the new conditions. But other of their characteristics are ecologically neutral, they have neither positive nor negative influence on the creatures' prospects of survival. With no forces pushing for a change, these neutral characteristics tend to remain unaltered.
We know that life on land evolved around 400 my ago, in the Devonian, and it is believed that it evolved from fish through amphibians and on to reptiles. The blood of higher land creatures contains an appreciable amount of salt, but much less than that in seawater, around 1% as opposed to 3.5%. On the other hand, modern marine fishes have a blood salt level similar to that of seawater.
The inference is that the salt level of the ancient seas was much less than that of today. To put a figure on this increase, if the change was regular from 1% to 3.5% in 400 my, this is a rate of increase of 0.006%/ my.
Proposition 10I
The average salinity of seawater has increased continuously
for at least the last 400 my
There is other evidence for this proposition. The most ancient groups of higher land plants with living descendants are the ferns and the cycads. Both these groups avoid saline water, being almost never found as seashore plants. The same is true of lower land plants, such as the mosses. This feature is understandable if, when these plants evolved (presumably from water plants), the seas were much less saline so that there was no incentive for these plants to develop the ability to live with salt.
On the other hand, plants which are at home in saline conditions are usually specialized members of younger, modern genera, such as the pistachio nut and the date palm. Some species of the recently evolved grasses, for example Distichlis (Australian beach grass), will grow when irrigated with seawater, and a tomato species native to the Galapagos Islands will actually grow in the sea. The ultimate is the group of seagrasses referred to in NU006, true flowering plants whose ancestors undoubtedly evolved on land before re-adapting to live entirely under the sea.
Similarly, specific adaptions to cope with a salty environment are found in sea-going representatives of what we would regard as land animals. These adaptions give the ability to excrete excess salt in some way, usually with a mechanism related to tears [53]. Seabirds secrete drops of an almost pure salt solution from nasal glands, shaking the drops off to eliminate salt. Normal land lizards do not produce tears, but the marine iguana of the Galapagos, the only sea-going lizard, does. Salt-water crocodiles 'cry', freshwater ones do not. And the only two land mammals with the ability to produce tears are man -- and the elephant.
The inference is that when life on land first developed, the seas contained water which was much fresher than that of the modern oceans. We can restate Proposition 10I from the viewpoint of the evolution of life:
Proposition 10J
Land creatures first evolved, around 400 my ago, from sea
creatures adapted to seawater much fresher than that of today
This proposition also fits in well with the other Earth-expansion evidence we have had in this suite of articles. As with the Earth's water (Proposition 10D), the salt available at the surface would increase as the Earth expanded and more rock was taken into the active-domain zone. But, in contrast to this water, the salt would not be partly lost into space, and so its concentration relative to the water would increase.
The fact that the oldest rock salt deposits are around 300 my old, while the first land probably appeared around 400 my ago (Proposition 10C), also fits. Rock salt deposits could not form until there was enough land to enclose seas or lakes, and conditions arose suitable to achieve virtually complete evaporation of these waters, such as uplifted low domains not circled by mountains (which would give rise to freshwater inflow from rains).
An interesting feature of salt deposits are that they are often associated with deposits of petroleum, mineral oils. We will return to this point, and its significance, in NU013.
Another interesting question is whether the chemical composition of the salts dissolved in seawater was different in former ages. We will look at evidence on this point in the next article, which deals with the Earth's atmosphere.
(Full list of references at NURefs)
[18]. S Warren Carey. Theories of the Earth and Universe: a history of dogma in the Earth Sciences. Stanford University Press, 1988.
[30]. Jane Ford. Scientists find ancient lake that flooded PNG land bridge. The Australian/ Feb 23, 1985.
[37]. Guinness Book of Records. N McWhirter, ed. Guinness, London, 1983.
[53]. Elaine Morgan. The aquatic ape. Souvenir Press, 1982.
[70]. Dennis Saunders & Perry de Rebeira. The birdlife of Rottnest Island. DAS & CPdeR, Western Australia, 1985.
[75]. W Somerville. Rottnest Island in history and legend. 4th ed. Rottnest Island Board, 1976.
NU011: The Earth's Atmosphere
NU009: Inside The Earth
Go to the NUSite Home Page
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Version 2.0, 2004, PDFs etc on World Wide Web (http://www.aoi.com.au/matrix/Nuteeriat.htm)
Version 3.0, 2014 Sep 25, Reworked from Chapter 10 of "Nuteeriat" as one article in a suite on the World Wide Web.