Physical preconditions for life by Kjell J. Tveter

Physical preconditions for life.

Science tells us that there are between 100 and 200 hundred billion galaxies in our Universe, and each galaxy has about 100 billion celestial bodies.  Our Earth is located in the galaxy called The Milky Way. It is hard to really understand how all these galaxies may originate from one single point with a size much less than the head of a pin at the Big Bang. We ought to be filled with awe when we make our reflections about our Universe, the Earth and Life

We use the word habitable to indicate that life is possible. And we speak about habitable and non-habitable zones. Science has done a lot if investigations to search for life in Cosmos, but so far life such as we know it, has only been found on our Earth.

The three most fundamental requirements for habitability are surface temperature, the presence of water and the composition of the atmosphere. The habitability of a planet depends sensitively on its water content. Water has to be present both as liquid, vapor and as ice. Life would not be possible if the water constantly existed as ice. Water is necessary for life. Water gives every appearance of being unique fit for the carbon based life that exists on earth. Every one of its chemical and physical properties seems maximally fit not only for microscopic life but also for large warm-blooded organisms like mammals as well as for the generation and maintenance of a stable chemical and physical environment on the surface of the earth. The circularity of water, falling down as drops, evaporation to form new clouds, calls for something greater than naturalistic randomness.

Water is a perfect solvent for organic substances. It is ideally fit as a solvent. The human body consists of 70 % water. The cells in our body could not be built by heavy elements or gases. A fluid is necessary, and water is unique in several aspects. Since I live in Norway where we have winter and frost, I find it astonishing that when the water temperature approaches the freezing point, water behaves differently than other fluids. Most of the time the warmest water is located on the surface and the cold water is located deeper. However, when the temperature falls below 4 degrees Celsius, the coldest water flows up and the warm water sinks. If the cold weather lasts, the water on the surface will freeze to ice, thereby preventing the sea or river from being ice-frozen from top to bottom. In this way the marine life is protected. The viscosity of water permits perfusion of blood even in the smallest capillaries, supplying the entire body with oxygen.

Our sun creates an electromagnetic spectrum that gives us both light and heat, which both are necessary for life. Almost the entire spectrum is hostile to life. A very tiny fragment of the spectrum is compatible with life. This small fragment makes up 1 part in 1025 of the total spectrum, and this tiny fraction hits our Earth.  1025 is the same as 1 nanometer out of 10 thousand billion kilometers.  So, we understand the scientists who find this an “astonishing precision”. This fraction of the sunlight is well suited for photosynthesis, a process which is absolutely necessary for life on Earth.

The Earth´s atmosphere is also optimal for life. One coincidence of great importance is the Earth´s atmosphere allowing 80 % of the sunlight to enter the Earth´s surface without being absorbed. If the atmosphere had contained substances that absorbed light, there would be no life here. We have to mention another coincidence as well: Water absorbs only a tiny fraction of the light that is necessary for life, while it absorbs damaging UV light. In this way light for photosynthesis reaches the plants in the sea.

Our Earth is very special. The Earth seems to have an optimal location for making scientific measurements and discoveries about Cosmos.

Our Earth has one moon. Some other planets may have more moons.  Our moon has many important functions.  First, it stabilizes the Earth´s tilt, or obliquity. This obliquity has an angle of 23.5 degrees. The moon has exactly the right mass to preserve this angle and to give the Earth its stability. This tilt of the Earth gives us the four seasons :  The spring, summer, autumn and winter.  This angle of 23.5 degrees supplies Earth with the correct wind systems to ensure rain for the soil. If this angle varied, one consequence would be regular occurrence of tsunamis that would be harmful for life, and urbanization. Another consequence would be a different climate, with hotter summers and colder winters.  The Earth rotates around itself. One such rotation takes 24 hours. The spinning of the Earth around itself has a velocity of about 1670 km per hour. Earth rotation is highly relevant to habitability. A planets rotation period will affect its day-night temperature

The Earth moves around the sun and makes one turn per year. Do you know that the speed of the Earth is about 107 000 km per hour. While we are sitting in our chair and have no feeling of velocity, we in fact move at a very high speed! This speed is fixed. If it were higher, our distance to the sun would increase for each turn, ultimately making us disappear into the Cosmos. If it were slower we would come closer and closer to the sun, eventually being engulfed by the sun.

Our universe is continuously expanding, this expansion rate is quite correct. A faster expansion will disrupt planets and stars, and causing all to be particles of dust. A lower expansion rate would cause too many black holes. So the expansion rate of the Universe has exactly the value that is necessary for our Universe to continue to exist.

Science has for many years investigated the sky, and have discovered a huge number of planets. Scientists have tried to find life in other places and on other planets, but without success. Much money has been spent on this research. The underlying reason is that If one would find life on other planets, one would conclude that life is able to originate spontaneously when the appropriate conditions are present.  In other words, if there is life on other planets, one would conclude that God is unnecessary. However, life as we know it has not been found at other places. We may wonder: Is the Earth unique among the planets? In these three short lectures I have given you, I have presented facts disclosing the extraordinary exactness that characterizes our Earth, a precision so astonishing that intelligent design seems to be the very best explanation.