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:
Approximately 4/5 of the atmosphere is nitrogen and this has been a major contributor to soil fertility. (See below.)
WaterThe 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.
AnimalsAnimals 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)
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.
Materials courtesy of plate tectonics and the moon
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.
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.
Author, 2077: Knights of Peace