Facing Reality About Life on Other Planets: Moon, Atmosphere, and Mass
This is a continuation of my discussion on the requirements for life to exist on a planet elsewhere in the universe. Facing Reality #1 listed 20 features and characteristics, all of which are required for life to exist and flourish. It also addressed the importance of our location in the galaxy. Facing Reality #2 addressed our location in the solar system and characteristics of our orbit. Now we will move in closer to our planet earth, and look at what our moon does for us, examine a little about the earth itself, and then discuss our atmosphere.
Earth has a satellite moon, about a quarter of a million miles away. It is about one-fourth the size of the earth, and in a nearly circular orbit around the earth. Each orbit takes just under thirty days – a month (from “moon-th”). This moon does a number of things for us, some of which are important to the support of higher forms of life.
First, the gravitational pull of the moon helps stabilize the tilt of the earth as it spins once a day. This tilt is important because it creates the seasons. As the earth progresses around the sun, making a complete trip in a year, direct sunlight varies throughout the year. For the summer solstice the northern hemisphere get more straight-on sunshine, for the two equinoxes the sunshine illuminates our sphere equally, then for the winter solstice the southern hemisphere gets more sun. Having these seasons fosters plant growth and re-growth in a cyclic pattern, giving us more productivity of plants—not to mention a more interesting environment to live in.
Second, the gravitational pull of the moon creates tides in the ocean and in the earth’s crust. Tides in the oceans are important since this is what stirs the water up, allowing it to absorb oxygen from the atmosphere (essential to marine life) and moves nutrients around. The movement of water from the ocean’s depths causes constant mixing; without it, the oceans would be stale water, not healthful to life forms (both plant and animal). The tidal action is minimal at the equator, and substantial at high latitudes, being as much as fifty feet of vertical movement in parts of Alaska. There the tides are such that one does not want to be trapped on one of the mud flats in the ocean inlets, as this much tidal action means the water rushes in and out faster than one can run.
The pull on the earth’s crust is not so noticeable, but does cause some movement on a geographical scale. This flexes the earth’s surface, and does facilitate tectonic movement under the crust. It helps the earth’s dynamics, freshening the surface and sub-surface mantle. Let me digress a moment with something that really impresses me.
There are a large number of features that do not relate to allowing life, but make life interesting. I have commented from time to time about features that allow scientific exploration related to an understanding of the universe and its principles. I note that the moon is of an exact size and location to exactly blot out the sun in a very precise way. The fact that we have solar eclipses that allow a special examination of the sun is remarkable. When the moon juxtaposes itself in front of the sun, often there is an exact fit to blot out just the sun, but not its atmosphere. When a total solar eclipse occurs, the sun’s atmosphere (the chromosphere), and its spectra can be recorded. Because of this tight fit, much was learned about the sun – one example being the discovery of the element helium. If the moon were 1% larger, the chromosphere would be hidden. If the moon were 1% smaller, there would be too much light to see the chromosphere (as occurs in annular eclipses) Fascinating!
Moving in even closer we come to the earth’s atmosphere. The atmosphere is very thin and is held in by gravity. The amount of atmosphere results in a gas pressure that is low enough to not crush delicate life and chemical structures. Some planets have an atmosphere that is destructively dense with correspondingly high pressures. Venus, for example, has a dense atmosphere of carbon dioxide with such pressure that it crushes spacecraft that have landed on the planet. That particular notorious ‘global warming’ gas also creates a greenhouse effect, making the atmosphere unsurvivably hot. Earth’s atmospheric pressure is high enough to supply oxygen to tissues in a quantity sufficient to facilitate metabolism.
Again, we see other factors that are just right, such as the composition of the earth’s atmosphere. Three main components comprise our atmosphere: 21% oxygen, 78% nitrogen and 1% carbon dioxide. The oxygen is necessary for metabolism. Too much oxygen would overwhelm the metabolic chemical reactions; i.e., they would in essence burn up. Too little oxygen would not support metabolic reactions. The nitrogen, although somewhat inert, provides enough substance to the atmosphere to maintain its thickness. Nitrogen is used by plants to build molecules such as amino acids, and thus is also a vital element for life. As we breathe, nitrogen helps sweep out our lungs, clearing out carbon dioxide, a waste product from our body metabolism. The low concentration of carbon dioxide provides enough carbon for plant growth. It also helps regulate the temperature of the atmosphere. There is much public concern about the amount of carbon dioxide in the atmosphere and the possibility of climate change. Just a small change in the carbon dioxide percentage can cause global changes in temperature. Some of the oxygen exists in the form of ozone in the high atmosphere which absorbs harmful ultraviolet light from the sun.
Another important role of the atmosphere is to transport water. As planets go, Earth’s atmosphere is generally pretty mild wind-wise. Some of the planets have violent windstorms with velocities of many hundreds of miles per hour. We have an occasional hurricane or typhoon, but, in general, winds are gentle. Water evaporates from the ocean and lakes and is carried around by our atmosphere. Clouds form and the water drops to earth as rain or snow, thus watering most of the continents. Although probably not a key requisite for life, the transport of water to wet the land is sure a good thing.
The inner planets have atmospheres of carbon dioxide, methane, oxygen, and nitrogen. The outer planets – the gas giants – are mainly hydrogen, helium, and traces of methane and ammonia. All the planets (except earth, of course) have atmospheres that would not support life. They also have temperatures that will not support life.
The mass of the earth is just right to create gravitational attraction sufficient to hold things to the surface, and to maintain our atmosphere. Too much gravity would make living structures (at least as we know them) have a difficult time growing and moving. Too little gravity would mean no atmosphere, so the mass of a planet needs to be within a certain range. The mass of the earth is distributed from the iron-nickel core, to the mantle, and to the subsurface material and the rocky surface.
In the next segment of this series, we will examine additional realities that must be faced to have a habitable planet, finding once again that the earth is right in the ‘Goldilocks Zone’ of being just right.
Dr Henry Richter, a contributing science writer to Creation-Evolution Headlines, was a key player at NASA/JPL in the early days of the American space program. With a PhD in Chemistry, Physics and Electrical Engineering from Caltech), Dr Richter brings a perspective about science with the wisdom of years of personal involvement. His book America’s Leap Into Space: My Time at JPL and the First Explorer Satellites (2015), chronicles the beginnings of the space program based on his own records and careful research into rare NASA documents, providing unequaled glimpses into events and personnel in the early days of rocketry that only an insider can give. His next book, Spacecraft Earth: A Guide for Passengers, is due out later in 2017. For more about Dr Richter, see his Author Profile.