Monday, 21 April 2014

Darwin's Wonderful Worms

Darwin's Meadow, Down House, Downe, Kent, UK
I was stimulated recently by an interesting question from a creationist which a friend passed to me for comments. Even creationists can sometimes pose interesting questions which need several minutes to think about. The question was, why are dinosaur tracks often found on the surface when human artifacts are often several feet below the surface. If dinosaurs are millions of years old why aren't they found at much deeper levels that human artifacts?

Superficially, this looks like a problem for evolution, and if it were true for every location it would indeed be. It would actually be equivalent to providing the evidence which the great J.B.S.Haldane said would falsify evolution - a fossil rabbit in the Cambrian. Of course, it isn't true for dinosaur tracks. All those found have either been in quarries or on the surface of eroded rocks such as the dry bed of Paluxy Creek, Texas, USA. But, old fossils are found on the surface or just a few feet down, so although my friend's creationist friend was wrong about the dinosaur tracks, there is a general question to be answered here.

The answer of course is that the surface of the Earth is dynamic and subject to forces of change, like erosion or human activity like quarrying and animal activity. Additionally, and more importantly, how fossils get exposed and how human artifacts get burried are two different processes entirely. The site of the Paluxy dinosaur tracks (the subject of the famous hoax that still has creationists fooled) is the bed of the Paluxy Creek, which has eroded away the upper layers, exposing the limestone layer with the tracks on. The dinosaur tracks found in Worth Matravers in Dorset, UK were exposed by quarrying for building material.

A lot of fossils are found in cliffs subject to coastal erosion and in exposed geological layers uplifted by plate tectonics but some can be picked up on the surface. I've spent many hours collecting fossil coral, ammonites and various other marine fossils from the Jurassic in a field in Buckinghamshire, and picking up heart urchin fossils made of flint from fields on the top of the Chiltern Hills in Southeast Oxfordshire. In both these cases the fields have been subject to human agriculture for at least 3,000 years during which ploughs have developed to plough deeper and be pulled with more power so today they can practically break up the bedrock.

At least in the chalk Chilterns, what is now the surface was once below a cap of sandstone which was deposited on top of the chalk and has long since mostly eroded away. In fact large slabs of this sandstone can still be found, as they were when the M40 was cut through the hill. Some of these can be seen at the side of the exit slip at Lewknor. Human activity continually churns over the surface of these fields bringing rocks from below up to the surface.

Tell Bari, Syria
Human artifacts, on the other hand, are often buried under the accumulated detritus of human activity. Ancient towns in Mesopotamia or Asia Minor actually stand on a mound or 'tell' of accumulated human refuse. Basically, until we had modern refuse collection and disposal, everything that came into a town, stayed there. Animal and human food which came into the town from the farms outside ended up eventually as the surface upon which new buildings were built.

New building materials were added to old building materials; clay was turned into pottery which ended up on waste-heaps or in dried up wells. Cartloads of goods came into the towns and hardly anything ever left. One of the main sources of this detritus was the mud bricks which were used for building but which quickly deteriorated.

Excavation at Tell Bari, Syria.
Note human figure centre for scale.
Today, archaeologists in these ancient places in the Middle East, India, China and Egypt works their way down through layers of human refuse, old buildings with their doorways now below ground when once they were at street level and modern roads run at what was once roof level or above. I've walked the streets of Luxor, the ancient Thebes of Ancient Egypt and one of the oldest continuously inhabited places in the world.

The streets are literally built of accumulated, compacted horse manure and other things I didn't want to think about, given that it hardly ever rains in Luxor and every passing lorry and car and horse-drawn cart throws up a cloud of fine dust. Only the main roads have a covering of tarmac. Don't even think of eating food from a road-side vendor unless you're pretty much immune to all known germs.

This brings me in a slightly rambling round about way to another important thing which, in the damper parts of the world at least, is a major cause of gradual, accumulated change in the surface of the Earth. It was something Charles Darwin himself worked out and wrote his last ever book about - the activity of earthworms.

Next to Down House, Darwin's home in Kent, is the meadow which he had known since his youth and in which he had spent countless hours just walking and observing the English wildlife at all times of the year. When he moved to Down House as a young man in 1842 he scattered some pieces of chalk over this meadow intending to check how deep they would be buried 'at some future period'. He returned to it again as an old man in ill health 34 years later and it led him to write his last book, The Formation of Vegetable Mould, Through the Action of Worms. In it, Darwin explained in meticulous details his observations on the power of earthworms to bury objects such as stones.

When we behold a wide, turf-covered expanse, we should remember that its smoothness, on which so much of its beauty depends, is mainly due to all the inequalities having been slowly levelled by worms. It is a marvellous reflection that the whole of the superficial mould over any such expanse has passed, and will again pass, every few years through the bodies of worms. The plough is one of the most ancient and most valuable of mans inventions; but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earth-worms. It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.

Charles Darwin, The Formation of Vegetable Mould, Through the Action of Worms P.313

Darwin's studies had included a study of the fallen stones at Stonehenge to measure how far they had been buried.

Darwin measured how much material they would ingest (eat), and how much they egested (pooped). He estimated how many worms there were on average in a given amount of soil, showing that all the soil in Britain ‘has passed many times through and will again pass many times through, the intestinal canals of worms’.

The rate at which worms process the soil can explain how ancient ruins are buried: Darwin calculated that worms push up eight tonnes of earth through the casts at the entrances of their burrows. He even carried out experiments to show this could happen within a human lifetime, he laid a stone in his garden, which was not to be disturbed, and measured the rate at which the earth was raised around it.

Darwin showed for the first time that worms increase the fertility of soils by aerating and mixing rotting material, this allows better root growth and water retention. By doing so he revolutionised compost heaps everywhere!

Charles Darwin & Evolution
©2009 Christs College, Cambridge, UK

During the course of this study, Darwin also showed that the 'denudation' of the southern English chalk downs was due not to coastal errosion as he had previously thought, but to the action of wind, water and frost. What he had previously thought were ancient coastlines were escarpments caused by aerial action on upfolded strata. This is still a fundamental principle of geology, and it of course, explains why ancient fossils can be picked up on the surface.

Some people have expressed disappointment that Darwin would devote his declining years to what, in retrospect, seems a rather trivial study for someone whose earlier works had been so profound and which had transformed Victorian attitudes to biology and human origins in particular and to science in general. I disagree with this view. For me it can be seen as the culmination of everything Darwin had discovered in his life's work and in particular how he had shown that what we see today is the result of a process of change, not of stasis, and how accumulated small changes can lead to big changes.

The world is not the product of a special creation and has remained unchanged ever since but is the product of a natural, formative and creative process requiring nothing more than the operation of nature. No magic need be postulated because no magic is required. The process is observable, falsifiable and can be used predictively. It is also, like Darwinian Evolution, so easy to understand that it takes real creativity to not understand it.

And underpinning the whole of his study is that same meticulous attention to detail, that same insistence that a conclusion must come only from evidence, a willingness to change his mind when the evidence requires it, and an enduring and contagious enthusiasm for his subject.

And (and this is especially pleasing) he answered the question posed by my friend's creationist friend by showing how those natural forces can account not only for fossil dinosaur tracks on exposed rock strata but also why human artifacts can be found often many feet below the surface.

Laughably for creationism, the answer to this 'killer' question has been known since 1881. That's only 133 years and about five generations ago. Obviously not nearly enough time for them to assimilate this new knowledge.





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3 comments :

  1. So it sounds like future archaeologists will have to excavate American cities from a "tell" of compacted cigarette butts and plastic bags. No worm ever born could survive trying to process that stuff.

    Seriously, this is fascinating, and not at all an unworthy matter for Darwin to spend his time on. It also helps explain why the surfaces of other planets look so stark and barren compared with Earth's (even Earth's deserts), and in many cases seem to have been completely unchanged for billions of years. Other planets don't have worms. Nothing churns up the soil on the Moon or Mars except the occasional meteorite.

    ReplyDelete
    Replies
    1. Absolutely. Life is literally creating the earth. Even the chalk in the chalk downs was extracted from seawater by trillions of microorganism called coccolithophores and deposited in vast drifts if tiny shells in marine sediment.

      Delete
  2. Some people have expressed disappointment that Darwin would devote his declining years to what, in retrospect, seems a rather trivial study ....

    But Darwin's path to greatness was begun also with a rather trivial study: of barnacles. It was only when he was ultimately reckoned as a world authority on barnacles that he used his reputation as a meticulous researcher to begin to promulgate his theory of evolution by natural selection.

    ReplyDelete

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