Oceanography

Of All the basic materials once thought to exist in superabundance, one of the most important is water. We must have a quart and a half each day to survive; our bodies are 70 percent water; our food cannot grow without it. It is as basic to us as air. Now it too is threatened.

This is the story of water itself-what it is, how it behaves and why, how it cycles from ocean to land and back again-a story of where water is and why it is salty, of why it rains or not. It is the story of the compound that has made earth unique in the solar system. The story of the Diamond Lens, in which a beautiful creature is seen to shrivel and die as the drop of water in which she lives evaporates, could become the story of earth. If this precious resource is ruined, life will cease.

Water is a continuous web, a network that unites the whole world we know. The vast mass of the oceans connects with streams and tributaries deep inside the continents, and water spreads from these through the pores of all rocks and soils. Ocean water evaporates into the atmosphere as a thin gas, thickening where it condenses into clouds. All life forms are really organized and controlled masses of water-tiny drops of watery fluid enclosed in delicate membranes. Only in the densest solids is the web broken, and even there, in rocks and bricks and glass, water cannot be denied forever. It filters slowly in; given time the solids erode and decay. The structures built by man are temporary victories against the spreading of the water web. If we could photograph the world with a film sensitive only to water, the shapes of all objects would remain, but their solidities would be altered and often reversed. Flesh would be dark and bones would be light. Oceans would be black and rocks nearly white.

The continuous web of water is far from static. Solar heat drives moisture from the oceans and continents by evaporation; gravity pulls it down as rain and the water runs back to the sea. The water in a tree is replenished thousands of times as the tree grows. The hundred or so pounds of water in a man’s body are replaced seventeen times a year. Water in the atmosphere is but twelve days old; while the oceans’ water is renewed by streams every forty thousand years.

Whence came this water that permeates and circulates, and why is it so important? Here we outline the story as we know it now; the record is fragmentary and stretches back five billion years to the beginning of the earth itself. The reconstruction depends upon current theories of the origin of the earth and of its history. Such theories keep changing and are refined and elaborated as more facts about earth history are discovered. The story here, then, is neither final nor immutable.

In the beginning the earth was built of an accumulation of meteoritic particles and of gases drawn from cosmic clouds. Its atmosphere, drawn from the same clouds, contained methane, ammonia, carbon monoxide, and carbon dioxide. Some time not long after this solid earth had grown to full size, the original atmosphere was lost. Such large outer planets as Jupiter and Saturn have atmospheres chiefly of methane, ammonia, hydrogen, and helium. These are the gases found in the cloudy parts of space and have been accumulated by planets of our solar system. The early earth atmosphere probably did not contain hydrogen and helium, for Earth was then so small that its gravitational attraction could not hold such fast-moving molecules captive.

As the earth grew in size it warmed, due partly to the heat engendered by its growth and compaction and partly to decay of radioactive elements such as uranium and thorium in the cosmic dust particles that were swept up by the growing earth. Within a few hundred million years the temperatures became so high that a molten stage was approached, and the originally homogeneous earth began to differentiate into “shells” of core, mantle, and crust. This may have been the time at which the first atmosphere was lost-the surface was hot, the rotation was speeding up, and the sun, also nearly newborn, was bombarding the earth with intense high energy radiation. All these factors would have helped to throw off and strip away the primary gaseous envelope of the primitive atmosphere.

As the earth surface then cooled and the “solar wind” from the sun diminished, a new atmosphere began to form. Such dense materials as iron and nickel sank to make the inner core; such lighter materials as aluminum, sodium, and potassium rose to make the crust. Still lighter substances emerged at the surface as gases, but were held within the strong inner part of the earth’s gravitational field.

Water vapor, almost absent in the primeval atmosphere, was the most important gas of the new one. With carbon dioxide, methane, carbon monoxide, hydrogen sulfide, and hydrochloric acid, the water came to the surface and remained as water vapor until the surface grew cool. Hydrogen and helium must have escaped from the interior in large quantities, but the earth could not keep them from slipping off into space. Oxygen was absent.

It is hard to imagine in the modem world, where water is a soothing, drinkable substance and oxygen is a requirement for life that our environment could have evolved from that deadly acid brew of 4Y1 billion years ago. But eventually the water vapor managed to condense to form the first ocean, and surface temperatures dropped below boiling. The acid gases began to be neutralized by the solid rocks of the surface until finally the seas were nearly neutral. When hydrochloric acid reacted with rocks, the acid was removed from the seas and from the atmosphere, releasing salts that dissolved in the ocean water. The carbon dioxide and hydrogen sulfide reacted with surface rocks to make various new minerals. The atmosphere was beginning to emerge in its present form.

What of the time scale of these events? The oldest rocks for which there are reliable ages are about 3Y2 billion years old; the first accretion of the earth has been placed at about 5 billion years, and the earth as we know it now, in terms of having a core, mantle, and crust, at about 4Y2 billion years.

So we can say that 4 billion years ago or so there was an ocean that it was salty, and at most slightly acid, that the acid gases had been abstracted from the atmosphere and fixed in rocks or as salts dissolved in the sea. We guess that the ocean of 4 billion years ago may have had a volume of at least one half of that of today. Just how much water vapor and other gases have been released from the earth’s interior since that time, or even how much are being released today, we do not know. There may have been continuous but irregular increase in the volume of the ocean.

Whether there were continents projecting above the early ocean, or whether the ocean covered the entire earth, is only to be guessed at. Perhaps the ocean spread around the globe, broken only here and there by a volcano building its cone from the sea floor until it rose above the surface. But, as soon as land appeared, the water cycles began that have carried on until today. When the water that was being ceaselessly evaporated from the sea to rain back upon the sea again fell instead upon the first volcanic island, it washed some loose rock down the slopes. Some of this rock dissolved in the fresh rain water (the salts had been left behind when the water molecules evaporated from the sea surface, speeded by the sun’s radiant energy) and was carried back to the sea. As the land struggled to grow the rains attacked it, battling to keep the sea surface unbroken.

The land has won-today the continents occupy thirty percent of the surface of the earth-but the struggle has been nearly an equal one, and there have been times when the sea nearly reclaimed its domain. Geologists continuously search for the remnants of the first land. A generation ago the oldest known rocks had an age of 2 billion years; now some have been found whose age is 3 billion years.

The most striking aspect of earth as seen from space is its abundant water. Great wreaths of white clouds make complicated patterns above the deep blue of the ocean background. Even when viewed from distances so great that all detail is lost, the bright colors and patterns of earth make striking contrast with the barren, dark, pitted surfaces of Mars and the Moon. We may be surprised, but the more we learn about our dry celestial neighbors the less likely it seems that life can exist upon them.

There are scientists who claim that there are billions of suns and that millions of them must have planets and that of these millions of planets there must be some just like earth where man could live. But as we learn more about how unusual the conditions on earth really are, and how complex a history was required to get it to its present state, we wonder whether among even millions of planets we could find a duplicate of earth.

When we look at the moon and the earth we can almost imagine that they were created as a pair especially to show the drastic differences that stem from the presence or absence of water. The moon preserves the scars of an eternity of bombardment by fragments of matter from space. Earth would have the same appearance were it not for the smoothing action of water. Only where there is a drastic lack of water and a recent meteorite fall, as at Meteor Crater in Arizona, is there a pit so young that it has not yet been obscured by the weathering action of water. There are some desert areas on earth, such as Death Valley in California, where aridity has immobilized the landscape to give it a moon-like quality-the trails of the gold seekers of 1849 can be followed as if they were made yesterday; pits dug by vanished Indians are unchanged except for a thin layer of dust and sand. There is also a silence when water is absent. No rustle of leaves or pounding of surf, no splash of rain or sounds of animals. All that is left is a silent, sun-baked landscape.

The moon did not surprise us with its lack of water, or even lack of an atmosphere. Even if an ocean were transported to the moon it would not remain; the water would evaporate, and the molecules of vapor would stray off into space. Venus and Mars have been a deep disappointment to those with hopes for other life within attainable distances. The atmosphere of Mars is thin and the moon-like nature of its cratered surface indicates that no sea or rain exists, even though there may be enough water vapor to make frost and ice at its white-capped poles. Venus is deeply shrouded in clouds but we know that its surface is so hot-300° F above boiling-that it has no ocean, nor is water vapor important in its atmosphere.

Mars and Venus and Earth all have densities about five times that of water. We assume that they must have formed by similar processes and from similar materials some five billion years ago. Presumably each is layered into core, mantle, and crust. Because of the differences in their distances from the sun, the energy each receives is not the same, but the earth probably would not change drastically if placed in either of the other’s orbits. All three planets have “secondary” atmospheres derived from their interiors. Yet only Earth has an ocean.

Having an ocean might be a special kind of phenomenon. On Earth, water vapor was the chief gas released from the interior when the “secondary” atmosphere was formed. Because the size and density of Venus are so similar to those of Earth, it is argued that the materials of which it was formed must have been similar. So Venus should have heated and cooled to form an atmosphere and an ocean like those of Earth. What happened? Why it is still hot and where is the water?

We can explain the differences between Earth and Venus in many ways. Let us suppose that they were the same when their crusts were nearly molten, and that their atmospheres were dominated by water vapor and carbon dioxide. What if, as they began to cool, the water vapor on Venus, a little closer to the sun and subjected to more intense radiations, was decomposed into hydrogen and oxygen by intensive ultraviolet light so that the hydrogen escaped and the oxygen reacted with the crust and was fixed there? This would remove water vapor from the Venusian atmosphere, leaving mostly carbon dioxide. Carbon dioxide (with its heat-retaining property) may have made it impossible for Venus to cool, so that the water has stayed eternally bound in its crust.

Whatever the answer to these speculations, there are clearly many ways in which a planet can lose its water. Apparently there is a very particular series of events that results in a planet with liquid water on its surface. Fortunately we have it, and have had it almost from the very beginning of the earth. As we shall see, however, this does not mean that we can afford to be complacent about our good fortune.

We can classify the period between four billion years ago and two billion years ago as the transition from an earth without oxygen to one with oxygen. There seems little doubt that some of the fossils from rocks two billion years old are the remains of simple green plants, so-called photosynthetic organisms that produce oxygen. Today’s plants are chiefly photosynthetic. They take in water and carbon dioxide in addition to a few minerals, and make from them the main constituents of their tissues, while releasing oxygen. The oxygen in turn is used by animals, who release carbon dioxide. The present balance is remarkable. The oxygen-producing green plants, which use up carbon dioxide, are exactly offset by the oxygen-using animals which release carbon dioxide. Biologists have developed a sealed container called a microcosm-a tiny world unto itself-into which they put plants and animals in just the right proportions so that the plants produce the oxygen the animals need, and the animals respond by giving off the carbon dioxide the plants require. This tiny sealed up world goes on functioning almost indefinitely. A stable reciprocal population is produced in the balanced microcosm; it neither grows nor diminishes. The moral as applied to the current population increase is too obvious to be further delineated.

We are fairly well convinced that the atmosphere of four billion years ago had no oxygen, and we are fairly sure that there were oxygen-producing organisms two billion years ago. We do not know when the atmosphere became oxygenated. Some of the organisms that developed in the oxygen-free early atmosphere learned how to use carbon dioxide and water to produce organic matter plus oxygen. For them the oxygen could be regarded as a waste product. But its influence on the environment was striking. The oxygen produced began to destroy some of the original gases such as hydrogen sulfide and methane, changing them to substances required for modem life-carbon dioxide and water.

After the deadly hydrogen sulfide and methane were removed, oxygen began to accumulate in the atmosphere. New organisms developed that used oxygen in their body functions, and the composition of the modem atmosphere began to be approached.

Our dating of these changes is poor indeed. Because there are some bacteria-like organisms found in rocks deposited more than three billion years ago, we can say that “life” existed even then. Whether there were oxygen producers at that time is unknown. Even though we are convinced that oxygen production by green plants was taking place two billion years ago, we still do not know how much headway had been made in producing enough oxygen to destroy the deadly hydrogen sulfide and methane in the earth’s early atmosphere.

There are hints that oxygen was present two billion years ago but it could not have been in significant amounts. In the famous African gold deposits of Witwatersrand, minerals occur in rocks that were almost surely exposed to the atmosphere at the time of their formation, yet these minerals could not form or persist in the presence of our modern oxygenated atmosphere, nor are they found in contemporary rock deposits. The great iron ores of Michigan, Wisconsin, and Minnesota, dated at little more than two billion years old, contain quantities of iron minerals that are not forming in significant amounts today because there is now too much oxygen present in air and water to allow their growth.

We are not sure there was a thoroughly modern ocean and atmosphere until recently in earth history. But there is agreement that for the last six hundred million years-a vast stretch of time, but only about 15 percent of total Geologic time conditions have been approximately as they are today. This is to say that the oceans had roughly their present volume and saltiness, continents were present with oceans around them, and the temperatures of land and sea were within today’s range. At times the seas partially covered the continents. The resulting greater oceanic area, as the seas crept onto the continents, kept temperatures more uniform than today so that climates were warmer and less differentiated into “belts.” Relations between land and sea kept changing with time. Recent studies show that the sea floors are rifting and spreading at rates of fractions of inches per year. Working this movement backward, we might find that two hundred million years ago South America was nestled against Africa!

Except for the continually changing and evolving life forms of both plants and animals, the scene was essentially modern. Water evaporated ceaselessly from the oceans and fell on the continents, collected into streams, and ran back into the sea. Both land and sea were inhabited by varieties of organisms; there were coral reefs, swimming creatures and burrowing creatures. The various environments were inhabited by organisms performing many of the same kinds of chemical and biological functions as those today, even though they have now been replaced by different species.

The volume of the oceans must have been about the same (even though the area changed as the oceans moved on and off the continents) and the amount of rain received by each square mile of continent about the same as today. Soils developed, water was absorbed into the ground, and lakes and marshes formed. We find in the rock layers deposited during those six hundred million years records of counterparts of all the environments we find today. There were periods of glaciations, recorded by boulder deposits and grooved rock surfaces. There were periods of widespread moderate climates, recorded by extensive coal deposits formed in swamps in which are found the bones of the great herbivorous dinosaurs.

Streams carried dissolved materials, as they do today, and washed along sand and mud to the oceans, as they do today. A picnic and a swim on one of the beaches of four hundred million years ago would be quite pleasant. The waves would not be higher, nor the tides different from today; we could breathe without difficulty, and we would get a moderate sunburn. The sea would be salty and would taste about the same as it does now. So for a very long time the patterns of the earth, if they could have been viewed from a satellite, would have been much the same.

Whether life has evolved within the limits of temperature set by the present earth environment, whether it could tolerate a much greater range, or whether the temperature range is limiting to life, we cannot know. But it is true that living forms inhabit almost every spot on earth, from the frozen tundra’s of Siberia to the hot springs of Yellowstone Park. Water that is actually boiling is too hot for life. The highest temperature at which living organisms carry on the basic processes of feeding and reproduction is 1870 F. The organisms that accomplish this feat are the blue-green algae. It is a tantalizing coincidence that the blue-green algae are among the oldest organisms in the geologic record of life. Continuous existence at temperatures below freezing is, of course, impossible for water-inhabiting forms, but terrestrial animals, like polar bears or penguins, do well in the Polar Regions.

The transition from inorganic compounds to living organisms that took place sometime before three billion years ago almost certainly required liquid water as the medium, and hence temperatures between freezing and boiling. Another requirement for the presence of life today is maintenance throughout time of earth conditions in which liquid water could exist. One of the advantages of having a great mass of ocean is its tremendous inertia in responding to an external heat change. Water requires more heat to change its temperature than does almost any other common substance, and enormous quantities of heat must be added to change it to steam or subtracted to make it into ice. So it may be that life on earth has survived through conditions of heating and cooling that would have frozen or boiled a lesser ocean and thus destroyed the watery web.

In the development of life on the primitive earth, we envisage two major steps. First is the synthesis of amino acids from the even simpler compounds that came from the interior of the earth, and second is the synthesis of proteins and similar complex molecules from the amino acids. The major elements of living cells are found in the proteins, and the unique character of the proteins depends upon the kinds and arrangements of the amino acids.

For a long time it seemed impossible to believe that the stupendous synthesis of proteins came from such simple starting materials as carbon monoxide (one carbon atom and one oxygen atom), carbon dioxide (one carbon and two oxygen), ammonia (one nitrogen and three hydrogen), methane (one carbon and four hydrogen) and water (two hydrogen and one oxygenH20). Mixtures of the simple compounds would sit together happily for years in the laboratory without any tendency to produce anything more complicated. Books were written about the impossibility of chance resulting in any complex substances that could reproduce themselves, one prime requisite of living creatures.

In 1953, Stanley L. Miller, then at the University of Chicago, performed an experiment that completely destroyed the earlier pessimism and showed that there were indeed reasonable path ways to the development of life under natural conditions. He simulated early earth conditions by mixing the gases methane, ammonia, and carbon monoxide (substances that are poisonous to most living things) in a flask, along with water vapor, and then repeatedly passed an electric spark through it. Brownish substances formed on the walls of the flask. Chemical analysis showed that these were amino acids, the building blocks of proteins. It was immediately obvious that lightning, striking through the early atmosphere, could have been capable of causing the first big step toward living things.

Since then a great variety of experiments have been performed using other sources of energy to cause combination of the simple compounds, and amino acids have been made simply by heating primitive gas mixtures to temperatures quite possible on the early earth.

There was a major problem, however, related to the absence of oxygen in the atmosphere at that time. Without oxygen, the ultraviolet light from the sun would reach the earth’s surface with a high intensity. One of the effects of high concentrations of ultraviolet rays would be to destroy amino acids. Many ingenious suggestions were made to obviate this difficulty-that synthesis took place too deep in the oceans for the ultraviolet to penetrate; that rock ledges protected the newly formed compounds, and so on. But none of the suggestions had a convincing ring; if deadly ultraviolet rays were reaching the surface every day, it would be extremely difficult to protect the new compounds long enough for further reactions to build the amino acids into proteins.

Philip Abelson, in 1966, turned the problem of ultraviolet light against itself by showing that sodium cyanide (one atom each of sodium, carbon, and nitrogen) when dissolved in water could actually be changed by ultraviolet light into a mixture of amino acids. Sodium cyanide, by the way, is a deadly poison to man!

We are still a long, long way from being able to tell how the first life was produced by natural processes from the simple substances from which it must have come. On the other hand, we know that amino acids can be built in nature fairly easily, and we also know that scientists are close to achieving the synthesis of life from amino acid building blocks, granting that laboratory conditions are highly controlled and are not those found in nature.

A single cell of a blue-green alga, it must be admitted, is still such a complex chemical system that, despite what has just been said, one still has grave doubts about the natural development of such a system. It is only necessary to watch under the microscope as a cell reproduces itself to have an intuitive feeling that natural chemistry is not sufficient as an explanation. The movements in the cell; the changes in the chromosomes, the governors of inheritance, as they knit together and then split longitudinally into mirror images; the construction of the cell into two new cells, each containing the same chromosomal content; and the growth of the two new cells into duplicates of the original, imply a volition or some vital force, unconscious as it maybe.

We stand at the moment, knowing that some of the steps toward first life are easier than we had thought; knowing that synthesis of something very close to life can be done in the laboratory, utilizing only materials that occur naturally; and still being appalled by the gap between the most esoteric laboratory work and understanding of the chemical complexity of the earliest organisms of which there is a record.

Perhaps we underestimate the eons of time available for the evolution of life. After one becomes used to it, one can talk about billions of years quite calmly. But if the earth is 5 billion years old, it means that the sun must have risen and set some 2,000 billion times, and 48,000 billion hours have passed. Between the formation of the oceans and the first life (some 33~ billion years ago) there are a billion years for combinations of compounds to take place, for the chance compound to win the battle with all the others.

Whatever the story of the origin of life, water was intimately involved. Cells, whether each is an organism sufficient unto itself or whether they are complexly organized into organs and tissues to form a human being, are mostly water; a complete cell analysis usually shows 60 to 70 percent water.

Even though it is dilute, the cell fluid is distinct from that of the outer environment, whether it is in a single-celled organism floating in the ocean, or in a muscle cell of a dog, bathed in the external watery medium of the other cells of his leg. The difference is caused by the cell membrane, a barrier between the internal and external cell environments. Much work has been done to understand how the membrane keeps the inside solution quite constant, despite changes in the outer environment, and yet manages to permit continuous “communication” between the fluid within and that without. Many scientists feel that the isolation of a watery system by a membrane, thus creating a cell, was a critical step in the development of life. Once a way had been developed to protect an inner chemical system from considerable changes in the outer environment there was a chance for continuity in the chemical composition inside, stability required for the production of nearly identical offspring when reproduction takes place.

It has already been said that the “flow through” of water in organisms is tremendous. Every three weeks our chemistry is renewed. Although the composition of the inner cell fluids remains almost constant, there is continuous exchange between the inside and the outside. Yet cells are not entirely immune to changes in environment. Cell fluids of most organisms are more dilute than sea water. If man is forced to drink only sea water, the contrast between cell fluids and sea water is too great to tolerate. If one drinks only sea water in large amounts the protective cell mechanism breaks down and death results.

The degree of tolerance between the cell fluids and the external environment has been a major factor in the distribution of the species of animals and plants. Most marine organisms, if placed in fresh water, die; the converse is also true. Biologists have studied salt tolerance in great detail and have concluded that the range of tolerance of most marine organisms is so limited that the salt content of the oceans cannot have changed a great deal in the last 600 million years or there would have been extinction of many marine species that have survived to the present.

On the other hand, there are some creatures that are almost impervious to changes in their external watery environment. Sharks, among the toughest and most successful of all marine animals, have been found in fresh water lakes. The salmon is born in fresh water but has most of its career in the oceans, returning to the rivers to spawn. The opening of the Great Lakes to the ocean via the St. Lawrence Seaway has permitted such normally marine species as the lamprey to invade the fresh water lakes and survive, to the sorrow of the lake trout and white fish.

We can view organisms as structures through which water passes rapidly and which try to maintain a constant internal economy in terms of their cell fluids-upon which depends their survival. They have different ranges of tolerance to the variations of the environment to which they are subjected. But water is all-important to them and they imbibe and excrete it rapidly. They are dynamic entities, changeable within short periods of time by the fluids they are fed, despite the protection afforded them by the cell membranes.

We must remember the strengths and weaknesses of cells when we think of the future. Living things have a remarkable flexibility but they cannot be pushed too far. If we change too greatly the waters on which they depend, they will perish not all at once, but in a sequence that may be quite upsetting to the continuance of man. 0