THE GREY BEGINNINGS
by Rachel Carson
"And the
earth was without form, and void; and darkness was upon the face of the deep" -
from Genesis.
Beginnings are apt to be
shadowy, and so it is with the beginnings of that great mother of life the sea.
Many people have debated how and when the earth got its ocean, and it is not
surprising that their explanations do not always agree. For the plain and
inescapable truth is that no one was there to see, and in the absence of
eyewitness accounts there is bound to be a certain amount of disagreement. So if
I tell here the story of how the young planet Earth acquired an ocean, it must
be a story pieced together from many sources and containing whole chapters the
details of which we can only imagine. The story is founded on the testimony of
the earth’s most ancient rocks, which were young when the earth was young; on
other evidence written on the face of the earth’s satellite, the moon; and on
hints contained in the history of the sun and the whole universe of star-filled
space. For although no man was there to witness this cosmic birth, the stars and
the moon and the rocks were there, and, indeed, had much to do with the fact
that there is an ocean.
The events of which I write
must have occurred somewhat more than 2 billion years
ago. As nearly as science can tell that is the approximate age of the earth, and
the ocean must be very nearly as old. It is possible now to discover the age of
the rocks that compose the crust of the earth by measuring the rate of decay of
the radioactive materials they contain. The oldest rocks found anywhere on earth
— in Manitoba —a re about 2.3 billion years old. Allowing 100 million years or
so for the cooling of the earth’s materials to form a rocky crust, we arrive at
the supposition that the tempestuous and violent events connected with our
planet’s birth occurred nearly 2.5 billion years ago. But this is only a minimum
estimate, for rocks indicating an even greater age may be found at any time.
The new earth, freshly torn
from its parent sun, was a ball of whirling gases, intensely hot, rushing
through the black spaces of the universe on a path and at a speed controlled by
immense forces. Gradually the ball of flaming gases cooled. The gases began to
liquefy, and Earth became a molten mass. The materials of this mass eventually
became sorted out in a definite pattern: the heaviest in the center, the less
heavy surrounding them, and the least heavy forming the outer rim. This is the
pattern which persists today — a central sphere of molten iron, very nearly as
hot as it was 2 billion years ago, an intermediate sphere of semi-plastic
basalt, and a hard outer shell, relatively quite thin and composed of solid
basalt and granite.
The outer shell of the young
earth must have been a good many millions of years changing from the liquid to
the solid state, and it is believed that, before this change was completed, an
event of the greatest importance took place — the formation of the moon. The next
time you stand on a beach at night, watching the moon’s bright path across the
water, and conscious of the moon drawn tides, remember that the moon itself may
have been born of a great tidal wave of earthly substance, torn off into space.
And remember that if the moon was formed in this fashion, the event may have had
much to do with shaping the ocean basins and the continents as we know them.
There were tides in the new
earth, long before there was an
ocean. In response to the pull of the sun the molten liquids of the
earth’s whole surface rose in tides that rolled unhindered around the globe and
only gradually slackened and diminished as the earthly shell cooled, congealed,
and hardened. Those who believe that the moon is a child of earth say that
during an early stage of the earth’s development something happened that caused
this rolling, viscid tide to gather speed and momentum and to rise to
unimaginable heights. Apparently the force that created these greatest tides the
earth has ever known was the force of resonance, for at this time the period of
the solar tides had come to approach, then equal, the period of the free
oscillation of the liquid earth. And so every sun tide was given increased
momentum by the push of the earth’s oscillation, and each of the twice-daily
tides was larger than the one before it. Physicists have calculated that, after
500 years of such monstrous, steadily increasing tides, those on the side toward
the sun became too high for stability, and a great wave was torn away and hurled
into space. But immediately, of course, the newly created satellite became
subject to physical laws that sent it spinning in an orbit of its own about the
earth. This is what we call the moon.
There are reasons for
believing that this event took place
after the earth’s crust had become slightly hardened, instead of
during its partly liquid state. There is to this day a great scar on the surface
of the globe. This scar or depression holds the Pacific Ocean. According to some
geophysicists, the floor of the Pacific is composed of basalt, the substance of
the earth’s middle layer, while all other oceans are floored with a thin layer
of granite, which makes up most of the earth’s outer layer. We immediately
wonder what became of the Pacific’s granite covering and the most convenient
assumption is that it was torn away when the moon was formed. There is
supporting evidence. The mean density of the moon is much less than that of the
earth (3.3 compared with 5.5), suggesting that the moon took away none of
the earth’s heavy iron core, but that it is composed only of the granite and
some of the basalt of the outer layers.
The birth of the moon
probably helped shape other regions of the world ocean besides the Pacific. When
part of the crust was torn away, strains must have been set up in the remaining
granite envelope. Perhaps the granite mass cracked open on the side opposite the
moon scar. Perhaps, as the earth spun on its axis and rushed on its orbit
through space, the cracks widened and the masses of granite began to drift
apart, moving over a tarry, slowly hardening layer of basalt. Gradually the
outer portions of the basalt layer became solid and the wandering continents
came to rest, frozen into place with oceans between them. In spite of theories
to the contrary, the weight of geologic evidence seems to be that the locations
of the major ocean basins and the major continental land masses are today much
the same as they have been since a very early period of the earth’s history.
But this is to anticipate the
story, for when the moon was
born there was no ocean. The gradually cooling earth was enveloped in
heavy layers of cloud, which contained much of the water of the new planet. For
a long time its surface was so hot that no moisture could fall without
immediately being reconverted to steam. This dense, perpetually renewed cloud
covering must have been thick enough that no rays of sunlight could penetrate
it. And so the rough outlines of the continents and the empty ocean basins were
sculptured out of the surface of the earth in darkness, in a Stygian world of
heated rock and swirling clouds and gloom.
As soon as the earth’s crust
cooled enough, the rains began to fall. Never have there been such rains since
that time. They fell continuously, day and night, days passing into months, into
years, into centuries. They poured into the waiting ocean basins, or, falling
upon the continental masses, drained away to become sea.
That primeval ocean, growing
in bulk as the rains slowly filled its basins, must have been only faintly salt.
But the falling rains were the symbol of the dissolution of the continents. From
the moment the rains began to fall, the lands began to be worn away and carried
to the sea. It is an endless, inexorable process that has never stopped — the
dissolving of the rocks, the leaching out of their contained minerals, the
carrying of the rock fragments and dissolved minerals to the ocean. And over the
eons of time, the sea has grown ever more bitter with the salt of the
continents.
In what manner the sea
produced the mysterious and wonderful stuff called protoplasm we cannot
say. In its warm, dimly lit waters the unknown conditions of temperature and
pressure and saltiness must have been the critical ones for the creation of life
from non-life. At any rate they produced the result that neither the alchemists
with their crucibles nor modern scientists in their laboratories have been able
to achieve.
Before the first living cell
was created, there may have been many trials and failures. It seems
probable that, within the warm saltiness of the primeval sea, certain organic
substances were fashioned from carbon dioxide, sulphur, nitrogen, phosphorus,
potassium, and calcium. Perhaps these were transition steps from which the
complex molecules of protoplasm arose — molecules that somehow acquired the
ability to reproduce themselves and begin the endless stream of life. But at
present no one is wise enough to be sure.
Those first living things may
have been simple microorganisms rather like some of the bacteria we know today —
mysterious borderline forms that were not quite plants, not quite animals,
barely over the intangible line that separates the non-living from the living.
It is doubtful that this first life possessed the substance chlorophyll, with
which plants in sunlight transform lifeless chemicals into the living stuff of
their tissues. Little sunshine could enter their dim world, penetrating the
cloud banks from which fell the endless rains. Probably the sea’s first children
lived on the organic substances then present in the ocean waters, or, like the
iron and sulphur bacteria that exist today, lived directly on inorganic food.
All the while the cloud cover
was thinning, the darkness of the nights alternated
with palely illumined days, and finally the sun for the first time shone through
upon the sea. By this time some of the living things that floated in the sea
must have developed the magic of chlorophyll. Now they were able to take the
carbon dioxide of the air and the water of the sea and of these elements, in
sunlight, build the organic substances they needed. So the first true plants
came into being.
Another group of organisms,
lacking the chlorophyll but needing organic food, found they could make a way of
life for themselves by devouring the plants. So the first animals arose, and
from that day to this, every animal in the world has followed the habit it
learned in the ancient seas and depends, directly or through complex food
chains, on the plants for food and life.
As the years passed, and the
centuries, and the millions of years, the stream of life grew more and more
complex. From simple, one-celled creatures, others that were aggregations of
specialized cells arose, and then creatures with organs for feeding, digesting,
breathing, reproducing. Sponges grew on the rocky bottom of the sea’s edge and
coral animals built their habitations in warm, clear waters. Jellyfish swam and
drifted in the sea. Worms evolved, and starfish, and hard-shelled creatures with
many-jointed legs, the arthropods. The plants, too, progressed, from the
microscopic algae to branched and curiously fruiting seaweeds that swayed with
the tides and were plucked from the coastal rocks by the surf and cast adrift.
During all this time the
continents had no life. There was little to induce living things to come
ashore, forsaking their all-providing, all-embracing mother sea. The lands must
have been bleak and hostile beyond the power of words to describe. Imagine a
whole continent of naked rock, across which no covering mantle of green had been
drawn — a continent without soil, for there were no land plants to aid in its
formation and bind it to the rocks with their roots. Imagine a land of stone, a
silent land, except for the sound of the rains and winds that swept across it.
For there was no living voice, and no living thing moved over the surface of the
rocks.
Meanwhile, the gradual
cooling of the planet, which had first given the earth its hard granite crust,
was progressing into its deeper layers; and as the interior slowly cooled and
contracted, it drew away from the outer shell. This shell, accommodating itself
to the shrinking sphere within it, fell into folds and wrinkles — the earth’s
first mountain ranges.
Geologists tell us that there
must have been at least two periods of mountain building (often called
“revolutions”) in that dim period, so long ago that the rocks have no record of
it, so long ago that the mountains themselves have long since been worn away.
Then there came a third great period of upheaval and readjustment of the earth’s
crust, about a billion years ago, but of all its majestic mountains the only
reminders today are the Laurentian hills of eastern Canada, and a great shield
of granite over the flat country around Hudson Bay.
The epochs of mountain
building only served to speed up the processes of erosion by which the
continents were worn down and their crumbling rock and contained minerals
returned to the sea. The uplifted masses of the mountains were prey to the
bitter cold of the upper atmosphere and under the attacks of frost and snow and
ice the rocks cracked and crumbled away. The rains beat with greater violence
upon the slopes of the hills and carried away the substance of the mountains in
torrential streams. There was still no plant covering to modify and resist the
power of the rains.
And in the sea, life
continued to evolve. The earliest forms have left no fossils by which we can
identify them. Probably they were soft-bodied, with no hard parts that could be
preserved. Then, too, the rock layers formed in those early days have since been
so altered by enormous heat and pressure, under the folding of the earth’s
crust, that any fossils they might have contained would have been destroyed.
For the past 500 million
years, however, the rocks have preserved the fossil record. By the dawn of the
Cambrian period, when the history of living things was first inscribed on rock
pages, life in the sea had progressed so far that all the main groups of
backboneless or invertebrate animals had been developed. But there were no
animals with backbones, no insects or spiders, and still no plant or animal had
been evolved that was capable of venturing on to the forbidding land. So for
more than three-fourths of geologic time the continents were desolate and
uninhabited, while the sea prepared the life that was later to invade them and
make them habitable. Meanwhile, with violent trembling of the earth and with the
fire and smoke of roaring volcanoes, mountains rose and wore away, glaciers
moved to and fro over the earth, and the sea crept over the continents and again
receded.
It was not until Silurian
time, some 350 million years ago, that the first
pioneer of land life crept out on the shore. It was an arthropod, one of the
great tribe that later produced crabs and lobsters and insects. It must have
been something like a modern Scorpion, but, unlike some of its descendants, it
never wholly severed the ties that united it to the sea. It lived a strange
life, half-terrestrial, half-aquatic, something like that of the ghost crabs
that speed along the beaches today, now and then dashing into the surf to
moisten their gills.
Fish, tapered of body and
stream-molded by the press of running waters, were evolving in Silurian rivers.
In times of drought, in the drying pools and lagoons, the shortage of oxygen
forced them to develop swim bladders for the storage of air. One form that
possessed an air-breathing lung was able to survive the dry period by burying
itself in mud, leaving a passage to the surface through which it breathed.
It is very doubtful that the
animals alone would have succeeded in colonizing the land, for only the plants
had the power to bring about the first amelioration of its harsh conditions.
They helped make soil of the crumbling rocks, they held back the soil from the
rains that would have swept it away, and little by little they softened and
subdued the bare rock, the lifeless desert. We know very little about the first
land plants, but they must have been closely related to some of the larger
seaweeds that had learned to live in the coastal shallows, developing
strengthened stems and grasping, root-like holdfasts to resist the drag and pull
of the waves. Perhaps it was in some coastal lowlands, periodcally drained and
flooded, that some such plants found it possible to survive, though separated
from the sea. This also seems to have taken place in the Silurian period.
The mountains that had been
thrown up by the Laurentian revolution gradually wore away, and as the sediments
were washed from their summits and deposited on the lowlands, great areas of the
continents sank under the load. The seas crept out of their basins and spread
over the lands. Life fared well and was exceedingly abundant in those shallow,
sunlit seas. But with the later retreat of the ocean water into the deeper
basins, many creatures must have been left stranded in shallow, landlocked bays.
Some of these animals found means to survive on land. The lakes, the shores of
the rivers, and the coastal swamps of those days were the testing grounds in
which plants and animals either became adapted to the new conditions or
perished.
As the lands rose and the
seas receded, a strange fishlike creature emerged on the land, and over the
thousands of years its fins became legs, and instead of gills it developed
lungs. In the Devonian sandstone this first amphibian left its footprint.
On land and sea the stream of
life poured on. New forms evolved; some old ones declined and disappeared. On
land the mosses and the ferns and the seed plants developed. The reptiles for a
time dominated the earth, gigantic, grotesque, and terrifying. Birds learned to
live and move in the ocean of air. The first small mammals lurked
inconspicuously in hidden crannies of the earth as though in fear of the
reptiles.
When they went ashore the
animals that took up a land life carried with them part of the sea in their
bodies, a heritage which they passed on to their children and which even today
links each land animal with its origin in the ancient sea. Fish, amphibian, and
reptile, warm-blooded bird and mammal — each of us carries in our veins a salty
stream in which the elements sodium, potassium, and calcium are combined in
almost the same proportions as in sea water. This is our inheritance from the
day untold millions of years ago, when a remote ancestor, having progressed from
the one-celled to the many-celled stage, first developed a circulatory system in
which the fluid was merely the water of the sea. In the same way, our
lime-hardened skeletons are a heritage from the calcium-rich ocean of Cambrian
time. Even the protoplasm that streams within each cell of our bodies has the
chemical structure impressed upon all living matter when the first simple
creatures were brought forth in the ancient sea. And as life itself began in the
sea, so each of us begins his individual life in a miniature ocean within his
mother’s womb, and in the stages of his embryonic development repeats the steps
by which his race evolved, from gill-breathing inhabitants of a water world to
creatures able to live on land.
Some of the land animals
later returned to the ocean. After perhaps 50 million years of land life, a
number of reptiles entered the sea about 170 million years ago, in the Triassic
period. They were huge and formidable creatures. Some had oar-like limbs by
which they rowed through the water; some were web-footed, with long, serpentine
necks. These grotesque monsters disappeared millions of years ago, but we
remember them when we come upon a large sea turtle swimming many miles at sea,
its barnacle-encrusted shell eloquent of its marine life. Much later, perhaps no
more than 50 million years ago, some of the mammals, too, abandoned a land life
for the ocean. Their descendants are the sea lions, seals, sea elephants, and
whales of today.
Among the land mammals there
was a race of creatures that took to an arboreal existence. Their hands
underwent remarkabledevelopment, becoming skilled in manipulating and examining
objects, and along with this skill came a superior brain power that compensated
for what these comparatively small mammals lacked in strength. At last, perhaps
somewhere in the vast interior of Asia, they descended from the trees and became
again terrestrial. The past million years have seen their transformation into
beings with the body and brain of man.
Eventually man, too, found
his way back to the sea. Standing on its shores, he must have looked out upon it
with wonder and curiosity, compounded with an unconscious recognition of his
lineage. He could not physically re-enter the ocean as the seals and whales had
done. But over the centuries, with all the skill and ingenuity and reasoning
powers of his mind, he has sought to explore and investigate even its most
remote parts, so that he might re-enter it mentally and imaginatively.
He built boats to venture out
on its surface. Later he found ways to descend to the shallow parts of its
floor, carrying with him the air that, as a land mammal long unaccustomed to
aquatic life, he needed to breathe. Moving in fascination over the deep sea he
could not enter, he found ways to probe its depths, he let down nets to capture
its life, he invented mechanical eyes and ears that could re-create for his
senses a world long lost, but a world that, in the deepest part of his
subconscious mind, he had never wholly forgotten.
And yet he has returned to
his mother sea only on her own terms. He cannot control or change the
ocean as, in his brief tenancy of earth, he has subdued and plundered the
continents. In the artificial world of his cities and towns, he often forgets
the true nature of his planet and the long vistas of its history, in which the
existence of the race of men has occupied a mere moment of time. The sense of
all these things comes to him most clearly in the course of a long ocean voyage,
when he watches day after day the receding rim of the horizon, ridged and
furrowed by waves; when at night he becomes aware of the earth’s rotation as the
stars pass overhead; or when, alone in this world of water and sky, he feels the
loneliness of his earth in space. And then, as never on land, he knows the truth
that his world is a water world, a planet dominated by its covering mantle of
ocean, in which the continents are but transient intrusions of land above the
surface of the all-encircling sea.
