Saturday, 25 April 2015

Our precious planet. Part 3. Built for civilization

Part 1 showed how the solar system is situated in a safe haven in the cosmos. Part 2  listed the factors which make the Earth itself unique for the development of life. 





This post deals with the special terrestrial conditions which allowed civilization to evolve.

Here they are, as far as I understand them:


Atmosphere

The oxygen content of the atmosphere is just right to allow fire (any more and all combustible material would  be ablaze, much less and we would not be able to breath). Fire has been an essential requirement for keeping warm as well as ore smelting, metal processing, cooking, medicine, heat engines, rocket motors and much else.

Approximately 4/5 of the atmosphere is nitrogen and this has been a major contributor to soil fertility. (See below.)
The atmosphere is relatively clear so that we can see celestial objects and deduce our place in the larger scheme of things. (See below.)

 Water

The different phases of water depend on the pressure exerted on them by the atmosphere and on the ambient temperature. On the Earth's surface  the pressure and the range of temperatures allows all three phases of water: solid, liquid and vapour. These conditions have existed for billions of years and allowed the development of biodiversity (e.g. by transporting pollen, viruses and bacteria around the globe in oceans and cloud aerosols).

Rivers, lakes and oceans have allowed exploration and  trade in bulk up to very large distances. They have also been a valuable source of fish, a staple food for most peoples and in combination with the atmosphere have kept the climate stable enough to permit
the  building and survival of cities. 

Largely through the Earth's unique  plate tectonics and crustal formation mechanism it has the right ratio of land to sea area (29%). The topography, the relative sizes of the continental land masses and the positioning of continents and  islands are also optimal. E.g. diverse societies evolve because they are separated and yet are still able to trade and interact, which usually leads to innovation and enrichment. 

 Soil                 

The surface soil in combination with a plethora of micro organisms have been suitable for agriculture, the main facilitator of civilization through human history. Lightning has been a crucial factor in extracting nitrogen from the atmosphere - nitrogen being a critically important nutrient for crops and other plants. Lightning also starts wildfires, leaving mineral-rich charcoal which improves the soil's ability to retain water. 

Animals

 Animals suitable for breeding, training and domestication (e.g. dogs, sheep, goats, oxen, horses, falcons) have been essential in allowing hunting, agriculture, transport and communication to develop. Even if animals had evolved on other planets they are unlikely to include these or even their equivalents. Dogs, e.g., have  unique DNA which permits extraordinary variability through breeding.



Location in the Milky Way Galaxy (MWG)

Our solar system, unlike most star systems, is so placed in the MWG as to afford good views of the universe. It also enables us to measure the cosmic microwave background (‘snow’ on the screens of certain TVs) from the nascent universe, providing evidence of the Big Bang theory. Had the Sun been placed in most parts of our Galaxy we would be totally oblivious to most of the universe and its history (in a sense we still are because it comprises largely dark matter and energy; but at least we are aware that there is something there waiting to be investigated). 

Order in the sky

 The ordered movements of the Sun, Moon, planets and stars in the sky, from night to night, day to day, a consequence of the Earth’s rare stable rotation, inspired the ancients to develop mathematics and mark the seasons for agriculture. The concept of an ordered universe was born. Largely unpredictable events such as exploding stars (supernovae), meteors and comets only served to emphasize the underlying order.
Also, the Moon is 400 x smaller than the Sun but 400 x nearer. This makes them appear to be the same size in the sky and results  in the extraordinary phenomenon of total eclipses which excited the curiosity of early man; and without curiosity, civilization can't develop.
 The resulting solar eclipses enabled modern man to learn about the Sun’s atmosphere and discover helium in the Sun before it was found on Earth .The identical apparent sizes of the Sun and Moon also allowed precisely timed eclipses and new moons to form the basis of a calender.

Ice cores, sediments and fossils

 Freezing of ice over millions of years has provided ice cores giving evidence for solar, supernovae, magnetic, atmospheric, volcanic and pollen phenomena over this period. Cores of lake sediments have also proved valuable records of the past, especially climate change. This evidence would not have been available without water occurring as both liquid and ice for billions of years. No other planet we know allows this. Understanding of history is important in allowing a people to advance.
Fossils of creatures preserved in sea deposits turned to rock have given us the ability to reconstruct certain aspects of the evolution of life over billions of years.

Materials courtesy of plate tectonics and the moon

Ores and minerals –e.g. copper, tin , iron, uranium and silicon - for materials technology have been made available through fine tuned plate tectonics. Hence the Bronze, Iron, Atomic and Silicon Ages (what next?). Note that plate tectonics, as far as we know unique to Earth,  are driven by the heat released during the decay of radioactive thorium and uranium produced in stars.
 A few months ago a paper in Nature showed that the formation of the Moon has played a critical role in preventing the 'iron-loving' heavy  elements (gold, silver, iron, titanium and others) needed for civilisation  from migrating  towards the Earth's core which would make them unavailable for mining. See this article by Hugh Ross



Energy

Vegetation and fauna for coal, natural gas and oil was deposited in time for use by technology-driven peoples. Even today areas once devoted to crops are being used for biofuel plants. 

The existence of hills and mountains, again the result of plate tectonics, together with water, results in fast flowing rivers and water falls which served as power sources alongside oxen etc. in pre-modern civilizations. Tidal and wave power is also used.

Nuclear fission has been a major carbon-free energy source since the 1960s and, like plate tectonics, depends on radioactive atoms made in stars. This form of nuclear power is likely to be replaced by nuclear fusion later this century. This is a much cleaner and should involve minimal environmental damage. In my novel (2077: Knights of Peace), this is the  main power source for the world at that time. Certain types of nuclear fusion technology look promising as power sources for interplanetary missions.


 Conclusion

These conditions, and probably many others, were key to the development of our civilization. No other planet discovered so far appears to have life; or, if it does, it has not evolved beyond bacteria or viruses, even over billions of years. Whatever the implications there is no doubt that humankind and the world it inhabits are in a class apart from the rest of creation.

John

Thursday, 16 April 2015

Our precious planet. Part 2: Built for Life



Photographs of the Earth from space are in themselves enough to make most people believe that our planet is unusual. But there is much more that science has revealed to show just how unusual it is, even leaving aside its placing in the galaxy and solar system  (see Part 1).

So I’ve tried to list some ways in which the Earth, unlike any other planet known to date, is suitable for life.



Formation of the Earth-Moon system

While the Earth was still hot rock another planet is thought to have hit it and caused myriad fragments to fly off, eventually coalescing in orbit to form the Moon. To help in the evolution of life (see below) the Moon had to be just the right size, mass and distance, and this in turn depended on the colliding planet having the right size, mass, momentum and angle of collision.
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Temperature and Distance from Sun

The Earth’s size and mass permit it to orbit in the ‘Goldilocks zone’ where the temperature is OK for life and the tidal forces do not lock it so that one side is always dark and cold while the other bakes.


Circular orbit and tilt of axis


Unlike all the other planets in our solar system the Earth has a near circular orbit which means the temperature is stable apart from gradual seasonal variations due to the tilt of its axis.
The north-south axis, about which the Earth spins, is tilted at an angle that stops the winters getting too cold and the summers too hot. Again, this is unique to Earth. The moderate changes of spring, summer, autumn and winter in the northern and southern hemispheres are in fact conducive to the thriving of life. In fact the tilt of the axis appears to be optimal for this – not too great, not too small.


Rotational speed and stability

The laws of mechanics lead to the planet spinning on its axis once in 24 hours, a rate which keeps night and day at a fairly even temperature. (Mars has about the same length of day but its air is very thin and there is no liquid water, so that its temperature varies wildly between night and day.)

The Moon spin stabilizes the Earth’s rotation and stops the axis wobbling too much. Without this conditions would be too chaotic for life to evolve. Note that the Moon had to be the right size, mass and distance to perform this role. No other planet we know about has such a favourably placed satellite.


Tides

Tidal forces due to the Moon and Sun permit the sea to gather life-enriching minerals as it dissolves them from the land when the tide is in.  Rivers also wash nutrients into the sea. The tides are likely to have played a role in the transition of life from sea to land. And certainly the lunar cycle both guides and influences many forms of life today.


Atmosphere and Ozone Layer

Today the air (nitrogen, oxygen, carbon dioxide and other gases) is right for the life of today. But when the early forms of life were evolving the composition was very different because life influences the atmosphere, adjusting its composition to suit itself. The atmosphere, in conjunction with plate tectonics, is also important in smoothing out temperature fluctuations and transporting clouds, viruses, bacteria, spores, insects, birds and dust around the globe.

There is a layer of ozone (a special form of oxygen which has 3 atoms per molecule instead of 2) which protects life from harmful ultraviolet radiation from the Sun. It was significantly damaged by CFC chemicals but is responding to restorative measures.



Water



Early forms of life are thought to have evolved and diversified in the oceans which cover three quarters of the Earth’s surface.  Comets, made largely of ice, hitting the Earth in its early stages appear to be the most likely source.  Alternatively the water could have come from the Earth’s interior or the cooling of the primordial atmosphere.

Minerals washed into the sea, especially salt, have maintained its salinity at an optimum level for life throughout geological time.

Water has the unique property of expanding when cooled down close to freezing point: were it not for this water would freeze from the bottom upwards and our oceans would be solid ice. we reside in the only known place in the universe where large expanses of  liquid water have existed for billions of years. Finally, water is optically clearest at the same wavelength that the Sun radiates most light - had it not been then photosynthesis would have been much less pronounced and insufficient to permit anything like the varied and abundant life with which this planet is blessed.

See also The deep mystery of existence.6. Water, the elixir of life.


Asteroid bombardment



Periodic hits by large asteroids (lumps of rock up to several miles in diameter) have been at a frequency and severity small enough to allow evolution to win over mass extinctions but big enough to spur the evolutionary process. Jupiter, Saturn and other celestial objects seem to have gravitationally tuned the arrival of asteroids to match this condition. There appears to be a remarkable degree of orchestration of these events. One current theory being investigated is that dark matter on the edge of the Milky Way Galaxy played a role.



Plate tectonics



Unlike any other planet we know of the Earth’s crust comprises large plates floating  on a subterranean ocean of molten rock. The heat needed for this comes from the decay of radioactive elements made in supernovas (U-235, U-236 and Th-232) billions of years ago. When the plates collide they cause earthquakes and volcanoes as well as force up parts of the crust to form land from which tides and rivers transfer life-giving nutrients to the sea. Crustal movements also bring up carbon dioxide into the atmosphere, essential for life, and, by a finely regulated process, bring ores to the surface layers where they can be mined.


Magnetic field



Because of the molten iron circulating inside the Earth we have a magnetic field  protecting us from lethal solar and cosmic radiation (the Van Allen Belts). Life today could not exist without it and no other planet we know of has anything like it, as far as we can tell.

I suspect there are hidden factors which make this an even more unlikely abode for carbon-based life. Carbon is necessary for any kind of life we can conceive of because C atoms are uniquely versatile in their capacity to combine with each other and with other atoms (valency) to form the structures and systems of the living world.


Reservoir of viruses and bacteria


Right from the earliest geological epochs, i.e. over billions of years,  it appears that viral and bacterial life were present. Where and how  these extremely complex and sophisticated organisms originated remains a mystery. The numbers are staggering. Placed end to end they would stretch millions of light years into space and they exist at  least miles down into the Earth's crust. There is a strong symbiosis between them and the rest of life. A human being has ten times as many bacteriums resident in his body as there are body cells (100 trillion vs 10 trillion, although the bacteriums are smaller). The evolution through geological time of the biosphere as a whole could well have been governed by or through them.


In Part 3 we see how the Earth is uniquely fitted to allow a high tech civilization to evolve.
Author 2077:Knights of Peace

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