A SHORT HISTORY OF THE WORLD H. G. WELLS3.THE BEGINNINGS OF LIFE
As everybody knows nowadays, the knowledge we possess of life before
the beginnings of human memory and tradition is derived from the
markings and fossils of living things in the stratified rocks. We find
preserved in shale and slate, limestone, and sandstone, bones, shells,
fibres, stems, fruits, footmarks, scratchings and the like, side by
side with the ripple marks of the earliest tides and the pittings of
the earliest rain-falls. It is by the sedulous examination of this
Record of the Rocks that the past history of the earth’s life has been
pieced together. That much nearly everybody knows to-day. The
sedimentary rocks do not lie neatly stratum above stratum; they have
been crumpled, bent, thrust about, distorted and mixed together like
the leaves of a library that has been repeatedly looted and burnt, and
it is only as a result of many devoted lifetimes of work that the
record has been put into order and read. The whole compass of time
represented by the record of the rocks is now estimated as
1,600,000,000 years.
The earliest rocks in the record are called by geologists the Azoic
rocks, because they show no traces of life. Great areas of these Azoic
rocks lie uncovered in North America, and they are of such a thickness
that geologists consider that they represent a period of at least half
of the 1,600,000,000 which they assign to the whole geological record.
Let me repeat this profoundly significant fact. Half the great interval
of time since land and sea were first distinguishable on earth has left
us no traces of life. There are ripplings and rain marks still to be
found in these rocks, but no marks nor vestiges of any living thing.
Then, as we come up the record, signs of past life appear and increase.
The age of the world’s history in which we find these past traces is
called by geologists the Lower Palæozoic age. The first indications
that life was astir are vestiges of comparatively simple and lowly
things: the shells of small shellfish, the stems and flowerlike heads
of zoophytes, seaweeds and the tracks and remains of sea worms and
crustacea. Very early appear certain creatures rather like plant-lice,
crawling creatures which could roll themselves up into balls as the
plant-lice do, the trilobites. Later by a few million years or so come
certain sea scorpions, more mobile and powerful creatures than the
world had ever seen before.
None of these creatures were of very great size. Among the largest
were certain of the sea scorpions, which measured nine feet in length.
There are no signs whatever of land life of any sort, plant or animal;
there are no fishes nor any vertebrated creatures in this part of the
record. Essentially all the plants and creatures which have left us
their traces from this period of the earth’s history are shallow-water
and intertidal beings. If we wished to parallel the flora and fauna of
the Lower Palæozoic rocks on the earth to-day, we should do it best,
except in the matter of size, by taking a drop of water from a rock
pool or scummy ditch and examining it under a microscope. The little
crustacea, the small shellfish, the zoophytes and algæ we should find
there would display a quite striking resemblance to these clumsier,
larger prototypes that once were the crown of life upon our planet.
It is well, however, to bear in mind that the Lower Palæozoic rocks
probably do not give us anything at all representative of the first
beginnings of life on our planet. Unless a creature has bones or other
hard parts, unless it wears a shell or is big enough and heavy enough
to make characteristic footprints and trails in mud, it is unlikely to
leave any fossilized traces of its existence behind. To-day there are
hundreds of thousands of species of small soft-bodied creatures in our
world which it is inconceivable can ever leave any mark for future
geologists to discover. In the world’s past, millions of millions of
species of such creatures may have lived and multiplied and flourished
and passed away without a trace remaining. The waters of the warm and
shallow lakes and seas of the so-called Azoic period may have teemed
with an infinite variety of lowly, jelly-like, shell-less and boneless
creatures, and a multitude of green scummy plants may have spread over
the sunlit intertidal rocks and beaches. The Record of the Rocks is no
more a complete record of life in the past than the books of a bank are
a record of the existence of everybody in the neighborhood. It is
only when a species begins to secrete a shell or a spicule or a
carapace or a lime-supported stem, and so put by something for the
future, that it goes upon the Record. But in rocks of an age prior to
those which bear any fossil traces, graphite, a form of uncombined
carbon, is sometimes found, and some authorities consider that it may
have been separated out from combination through the vital activities
of unknown living things.