CHAPTER SIX
THE LIVING EARTH

Humans are incredibly robust creatures considering we are little more than animated bags of water hanging on a mineral frame.

We can withstand difficult conditions and even survive without food for many weeks, yet we die quickly without air to breath or with direct exposure to unusually high or low temperatures. It is thanks to eons of Darwinian evolution that we are perfectly designed for our environment but perhaps we should not be too casual about the extraordinary good fortune that brought us to this point.

Every human is very special. We differ from other creatures, so we are told, because we are able to define ourselves by our own self-awareness resulting in a situation where there is a simple polarity to the Universe.

We all know that:

'There is me and then there is everything else.'

Each and every one of us is an emotional-intellectual island connected to that 'everything else' by the complex interaction of our five senses.

Two small regions of our skin have developed the ability to decode energy reflections in the form of sight, two m ore make sense of a cacophony of colliding compression waves in the gases around us giving us hearing.

Then we have skin sensitive enough to tell us about shape and texture, a mouth that accurately differentiates between different chemical substances we are about to consume in the form of taste and we have an air inlet that can pick out the presence of a specific molecule within a million others in the atmosphere as the sense we call smell.

These five connection modes cause us to have interaction with the 'everything else' - especially other humans, so we do not exist alone.

These points of stimulus combine to give life to the most remarkable array of aspects of self. Love, fear, loathing, compassion, laughter and countless other emotions make us special and m ark us out as entities that are utterly different to the rest of creation.

But,

• How and why have we become so spectacularly differentiated from other combinations of recycled stardust?

• What makes Neil Armstrong more special than the 3.5-billion-year-old rock he first lifted from the lunar surface?

Those with religious faith turn to their interpretation of God to explain the unexplainable and the more scientific amongst us turns to the Anthropic Principle.

The good old 'Anthropic Principle' is less there to help us answer the BIG question than to avoid having to deal with it. It accepts the vanishingly tiny probability of human existence by stating that the rules of the Universe that produced us have to be exactly as they are or we would not be here to perceive them.

To us, this is rather like defining moving, emotionally stimulating music by merely expressing it as 'music that is good'. The statement is correct but it does not compare with the experience!

What the Anthropic Principle does is to stop us worrying too much about the fact that we really have no right to exist. Of the two approaches, anthropic or divine, at least the God scenario is an attempt to move the problem on a notch rather than utilizing a principle that seems to have been conceived to ignore it.

Most scientifically minded people probably subscribe to the theory that humans, like everything else, are the product of billions of years of random chance. However, the most famous scientist of all time, Albert Einstein, was very unhappy about nature being based on randomness. He said about quantum physics: 'God does not play dice.'

The more we looked into how our planet developed into a paradise for living creatures the more surprised we became.

The miracle of life on Earth is due to our narrow temperature band that provides us with liquid water and, as we have explained, it is the Moon that is responsible for maintaining the perfect tilt that provides our benign climate. But amazingly, it was the very act of the Moon's creation that produced the first link in the chain of events that would lead the Universe to make you!

In 1911 a brilliant young scientist by the name of Alfred Lothar Wegener was browsing through the library of his university in Marburg, Germany, when he came across a scientific paper that listed a host of identical plant and animal species that could be found on opposite sides of the Atlantic.

Although having obtained a PhD in astronomy at a very early age, Wegener was particularly interested in geophysics, a field of study that was in its infancy at the time.
 

Something in the paper caught

Wegener's imagination and he began to spend time looking for other examples of similar plants and creatures separated by oceans.

There was, at the time, no reasonable explanation as to how such a state of affairs could have com e about. It had been postulated that the solution to this puzzle had to be land bridges that must have existed in very ancient times and that had allowed both plants and animals to move between continents. However, there were many examples that could not be explained in this way.

Wegener had also noted, as had others before him, how many cases there were in which the coastline of one continent looked as though it could fit snugly into that of another, such as the west coast of Africa and the east coast of South America.

He also found that if the continental shelf is studied, rather than the apparent coastline shaped by current sea level, the fit is often very much better.

Alfred Wegener began to ask himself if the answer to these anomalies might lie not in land bridges but in the fact that the continents were once joined together in one large continent, and that this had somehow broken up and drifted apart.

Later in his life he wrote about this process of logical deduction.

'A conviction of the fundamental soundness of the idea took root in my mind.'

Wegener spent a considerable period collecting further examples of extended flora and fauna and the available evidence continued to support his early theory.

For example, he found the fossils of plants and creatures in places where the climate must have been significantly different when they were alive and flourishing, such as fossilized cycads - ancient tropical plants found as far away from the tropics as Spitsbergen in the Arctic.

From the weight of evidence he had collected, Wegener deduced that all the continents had once been part of a single landmass, which he chose to call 'Pangaea' - a Greek word meaning 'all the Earth'.

He suggested that this supercontinent had broken up and had begun to drift apart 300 million years ago.

He called the process 'Continental Drift' and although he wasn't the first to suggest that there had originally been a single continent, he was able to provide substantial evidence to back up the claim. Wegener first published his findings and his hypothesis in his book The Origin of Continents and Oceans.²⁰

Although it was brilliantly argued, his ideas were not widely accepted at the time. A flood of scientific indignation broke over Alfred Wegener.

This happened for a couple of reasons: firstly, his theory was revolutionary, which inevitably clashed with the conservative tendencies of other experts; and in addition, although Wegener was certain that continental drift must have taken place, he had no theory as to how or why this might have happened.

The best he could suggest was that the continents, influenced by centrifugal and tidal forces as the Earth spun on its axis, were simply ploughing their way across the surface of the planet.

Dissenters pointed out that, if this was the case, the coastlines of the continents could hardly be expected to have remained so similar to the original 'fit' that it could still be observed. On the contrary, they would have been distorted beyond recognition. It was also suggested that tidal and centrifugal forces would be far too weak to move entire continents.

Poor Alfred Wegener didn't have the chance to look too much further into the matter; he died in 1930 whilst taking part in a rescue mission to deliver food to a party of explorers and scientists trapped in Greenland.

Wegener did have some notable supporters but in general his ideas remained on the shelf until as recently as the 1950s, by which time greater exploration and understanding of the Earth's geophysical makeup had begun to catch up with the idea of continental drift.

The truth of the matter is that Wegener was wrong in terms of his suggested mechanism, but quite correct in his basic assumption. Rather than ploughing their way across the planet's surface, the continents 'float' on what is known as the 'asthenosphere', the underlying rock of our planet.

This is under so much pressure and becomes so incredibly hot that it acts more like thick treacle than solid rock.

 

Figure 12
 

One of the factors that made Wegener's ideas m ore acceptable was the study of mountain ranges.

An earlier position held by many experts had been the 'contraction theory'. This suggested that the Earth had begun its life as a molten ball and that as it cooled it had cracked and folded up on itself.

This folding, the theory suggested, was what had created mountain ranges. The real problem with the contraction theory was that all mountain ranges should therefore be of the same age and it was rapidly becoming apparent that this could not be the case. Wegener had suggested that mountains were constantly being created as landmasses came into contact, exerting unbelievable pressure and pushing up land at or close to the points of contact.

Just a year before Alfred Wegener's death some corroborative evidence had been forthcoming, but it wasn't well accepted at the time.

In 1929 Arthur Holmes, a physicist at the Imperial College of Science in London suggested that the mantle of the Earth undergoes 'thermal convection'. The Earth's mantle is that region immediately below the outer crust. It extends all the way down to the Earth's core. Its composition varies with increased pressure and temperature but it makes up the biggest part of the Earth.

Holmes knew that when a substance is heated, its density decreases. In the case of the mantle this would cause material to rise to the surface where it would gradually cool, become denser and then sink again.

A similar process takes place with porridge that is boiling in a saucepan. Holmes was quite taken with Wegener's idea of continental drift and suggested that the tremendous pressures caused by thermal convection could act like a conveyor belt. This might cause the continents to break apart and to be 'carried' across the surface of the planet.

For years these ideas were dismissed, until knowledge caught up with the theories.

By the 1960s there was a greater understanding of the 'oceanic ridges'-regions where, it was being realized, Holmes' thermal convection might actually be taking place. It was also realized that oceanic trenches occurred, together with arcs of islands, close to the continental margins. All of this meant that convection was not only probable but certain.

Two other scientists, R. Deitz in 1961 and Harry Hess in 1962 separately published similar hypotheses based on mantle convection currents, and continental drift becam e universally accepted.

Deitz and Hess between them modified Holmes' original theory of convection and came eventually to their own mechanism for continental drift, which is based on what they termed 'seafloor spreading'. This spreading, it is suggested, begins in the mid-oceanic ridges. These are huge mountain ranges in the middle of the Earth's largest oceans.

So large are the mid-oceanic ridges that they are higher than the Himalayas and are more than 2,000 kilometers wide. Associated with the ridges are great trenches that bisect the length of the ridges and which can be as deep as 2,000 meters. The greatest heat flow from the ocean floor takes place near the summit of the mid-oceanic ridges.

There are also far m ore earthquakes on and around the ridges than are experienced elsewhere, showing these to be geologically active areas.

An increase in understanding of the Earth's magnetic field led to the realization that periodically this reverses. Such fluctuations can be detected with a device called a magnetometer.

It was discovered that, either side of the m id- oceanic ridges, it was possible to detect these past reversals in the Earth's magnetic field. The conclusion was that new material was constantly being thrown up on the ridges and was being pushed outwards on either side.

The reversals of the magnetic field demonstrated that this process was ancient but that it was still taking place.

Also of interest were 'deep-Sea trenches'.

The trenches are generally long and narrow and they are often associated with, and parallel to, continental mountain ranges. In addition they run parallel to the ocean margins. There is great seismic activity associated with the deep-sea trenches, indicating that they too are associated with the process of seafloor spreading and that they are directly related to the oceanic-ridges.

What is now thought to be happening is as follows: underneath the Earth's outer crust is the asthenosphere. This is a malleable layer of heated rock. It is kept hot because of radioactive decay in elements such as uranium.

The source for the radioactivity, which also includes thorium and potassium , lies deep within the planet. The asthenosphere, constantly heated, rises to the surface, pushing new material out at the mid-oceanic ridges. Magma escapes along the cracks formed at the ridges, forcing the new seafloor in different directions.

The new material spreads outwards until it makes contact with a continental plate and will then be 'subducted' beneath the continent. The lithosphere at this point sinks back into the asthenosphere, where it once again becomes heated.

Few experts disagree with this basic explanation, partly because it can be seen at work. India, for example, started its life on a completely different part of the planet. It is now being forced up into the body of Asia and the Himalayas are the result - a huge mountain range forced up by the pressure of the two landmasses meeting.

The whole process is known as plate tectonics and scientists were keen to see whether or not a similar process was taking place on the other terrestrial-type planets in our solar system - Mercury, Venus and Mars.

Probes sent to these planets have now shown conclusively that plate tectonics do not take place on any of our companion worlds, making it a strictly Earth-bound phenomenon, at least as far as our own solar system is concerned.

This is something of a puzzle.

• What is taking place in the Earth system that is so different from the other Earthlike planets?

• What caused plate tectonics to commence in the first place and what is the engine that keeps driving the process?

There is a growing body of evidence to show that in both cases the answer is almost certainly the Moon.

What is m ore, it is now being suggested that without plate tectonics the Earth may not have proved to be a suitable haven for life at all.

Dr Nick Hoffman, a geophysicist at the Department of Earth Sciences, Melbourne University, Australia, has recently suggested that the Moon m ade plate tectonics happen simply by coming into existence.

As we have discussed, the origin of the Moon is still shrouded in mystery, no matter how much proponents of any specific theory of its origin may pretend. However, there are certain facts that are known for sure.

As we have seen, the Moon is definitely made of the same stuff as the Earth, but not all of the Earth. Rather the composition of the Moon closely resembles the material in the Earth's crust, without many of the heavier components, such as iron, that make up the Earth's core.

But how could such a large amount of the Earth leap from the planet's surface into a position tens of thousands of miles in space?

Scientists were puzzled. And then a potential explanation was put forward in the form of the original Big Whack theory - the suggestion that maybe some object, about the size of Mars, collided with the young Earth and that the Moon was formed from surface material that was blasted off the face of the infant Earth.

There did not seem to be any other possibility, so it is now regularly taught as though it is a fact. The major problem of the Earth's current speed of rotation was tentatively explained away by proposing a second impact from the opposite direction occurring quite soon after the first.

To us this sounds like a rather desperate scenario to believe in. And as we have seen, other problem s remain for this would-be explanation; not least the question of where the material from the incoming objects went to.

If the Double Whack theory as correct, the Moon should be made up of three different sets of material, but it is not. It is made of Earth rock alone.

Nick Hoffman, as an acclaimed expert on the terrestrial planets within our solar system, has suggested that the removal of the material that went to make the Moon may have triggered plate tectonics by creating the space for the planet's skin to shift.

He points out that on Venus, for example, the same sort of forces are at work but the crust of the planet is so thick, the stresses within the crust simply cancel each other out, with the exception of a few wrinkles here and there.

Hoffman has noted that if the seventy per cent of Earth crust that was destined to become the Moon was returned to the Earth, it would 'fill the ocean basins with wall-to-wall continent'.

What would the Earth be like without plate tectonics?

Hoffman suggests it would be a water world, covered with oceans and with only the tips of extremely high mountain ranges poking out above the surface of the water. Of course there is nothing to suggest that life could not have existed on such a planet and Hoffman agrees that life is most likely to develop in a watery environment.

It's a fact, though, that what we term as being 'intelligent life', such as our own species, has developed on land.

The use of fire would not be possible in a watery habitat and the use of tools, one of the factors that is generally accepted as the starting point of our advance, is also a dry land phenomenon.

In any case, as we will see, the Moon is so important in other ways that even a watery world may have proved to be impossible without its existence.
 

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