Level: Introductory

Just right location

Believe it or not, a lot of scientists think fondly of the story of Goldilocks and the three bears. You know, the story in which Goldilocks found that the bowls of porridge left behind in the bears’ house were either too hot, too cold or finally just right. Well, guess which category the scientists think applies to planet Earth? If you guessed “just right”, that Earth lies in a Goldilocks region in space, then you would be right too. It is a fact that everything about our planet is so perfectly designed, that scientists are totally astonished. Many cannot explain the amazing conditions of our planet that make it perfect for living creatures. But we know why this is so, God made it this way.

Firstly the Sun, the centre of our solar system, releases mainly light and heat. These are the forms of energy that our planet needs to support life. Light provides energy for photosynthesis and heat warms up our atmosphere and rocks to a point well above the freezing point for water. (Living cells need liquid water not ice.) This is a happy circumstance that planet Earth sits at a distance from the Sun that is perfectly located to benefit from the radiation. If Earth were closer, our planet would heat up too much, and if it were farther away, it would be too cold. Our actual position lies in the “habitable zone”, just right for life, or (you guessed it) the Goldilocks zone.

Biosphere itself

Moving on to planet Earth itself, we discover the biosphere, the narrow zone around Earth that harbours life. It is the rocks, water and air that constitute the biosphere. They are the theatre in which the drama of life takes place. We soon discover that they have to be just right for life to thrive.

Air

The main gases in the air are nitrogen (N₂), oxygen (O₂), carbon dioxide (CO₂) and water vapour (H₂O). Of these gases, nitrogen makes up almost 79%, and oxygen makes up almost 21%. Carbon dioxide is a very small proportion of the air (0.04% percent) and water vapour varies around 0-4%. The combined characteristics of this gas mixture are just right for supporting life on earth.

Humans and other large creatures need a lot of oxygen in order to breathe and keep their bodies adequately supplied with oxygen. Nitrogen gas, at almost 80% is important for very different reasons. It provides bulk to the air, which prevents water molecules in the sea and elsewhere from evaporating too quickly. Otherwise the oceans would dry up and there would be no hydrological cycle to support life. Neither nitrogen gas nor oxygen gas absorb heat energy from the sun. This is a very good thing because if they did, Earth could become a very hot lifeless planet like Venus.

Nitrogen is essential in living cells but it is nevertheless very resistant to reacting chemically.  This preserves its presence as nitrogen gas in the air. If the nitrogen levels declined, then water would evaporate too quickly from water bodies. Only a few microbes with special metabolic processes are able to use N₂ to form NO₃ which plants can use to support life. [see nitrogen cycle under rocks]

Carbon dioxide gas is essential for photosynthesis. The fact that this gas also readily dissolves in water, means that it is available for living cells. Carbon dioxide also famously absorbs heat energy which helps to keep our planet at favourable ambient temperatures.  Some scientists have expressed concern that we now have too much carbon dioxide in the air and that the planet could heat up too much. Others say that Earth’s weather systems are complicated and the scary conclusions are unwarranted.

Water vapour is another gas that absorbs heat and so warms the atmosphere. Water’s complex characteristics however mean that water vapour exerts a modifying effect on climate so that cold temperatures are not as cold as they would be if the air was dry, and warm temperatures are not as warm as they would be if the air was dry. This is why deserts are affected by extreme of heat during the day and extremes of cold at night. They lack water vapour in the air.

Of all known substances, only water exists in all three possible states in the temperature range that we find on Earth. Thus this substance is the only one that could drive weather systems and the hydrological cycle which provides the necessary conditions for organisms to live on Earth. If there is no water, there is no life. If water evaporated, but did not come back to earth as rain, we could not live. [see hydrological cycle]

Rocks

The surface rocks are solid at temperatures that we find on Earth. They consist of silicon and other minerals, many of which are very important for the metabolism (life processes) of living cells. What is more, some rocks are more easily eroded than others. The resulting soils are very important indeed for supporting living creatures, especially plants. It the rocks were not solid, there would be no platform to support life on land and no basins to contain the oceans. Some very important nutrients are found in rocks and sediments eroded from rocks.

Nitrogen cycle

Nitrogen gas is a very stable gas that does not react easily. If it did react easily, then the necessary amount of this gas in the atmosphere would be hard to maintain. There are just a few microbes in the soil that are able to fix nitrogen (get nitrogen to react chemically). Bacteria like Rhizobium and a few blue green algae are able to fix nitrogen. Some plants like clover and beans (legumes) and alder trees harbour bacteria like Rhizobium in their roots.  

Rhizobium and other nitrogen fixers convert nitrogen gas into nitrates which plants absorb through their roots. All organisms need nitrogen to form proteins and genetic material (DNA). Consuming organisms eat plants and use the N in their own metabolisms. Decomposers turn proteins and DNA back to nitrates or ammonia which plants take up again. In some waterlogged areas, denitrifying bacteria turn nitrates and ammonia back into nitrogen gas. Thus, there is a loss of nutrients to the system and this is why we need nitrogen fixing bacteria. Without living nitrogen fixing bacteria, there is at least lightning which causes some nitrogen gas to react with oxygen, producing a small amount of nitrates.  But the amount would be far too little to sustain life.

Phosphorus cycle

This mineral in the form of phosphates is extremely important for living cells. Without it, there is no chemical energy carrier in cells to keep the metabolism going. Phosphate however is available on Earth only in very short supply. The best option for plants is to obtain phosphates from the decay of previously living organisms or from animal droppings and sewage. There are very low levels available in rock, much of which came from organisms which lived in the past.

Since plants must cope with very low availability of phosphates, unusually high levels of this nutrient can lead to too much plant material (pollution) or too much plant material of the wrong sort. Lakes with no outside source of phosphates other than the rocks, tend to be nutrient poor and harbour low populations of fish and other creatures. Lakes with high outside sources of by products from organisms (sewage runoff for example) may exhibit high levels of unwanted algae and fish populations.  Between the two extremes, a happy medium condition is possible.

Water

Water is extremely important for life. We cannot say this too emphatically. If there is no water, there is no life.

Let us review the characteristics of water that make it so important. Firstly, water is unique in that it can exist as a solid, liquid or gas at the temperatures that exist at Earth’s surface. No other substance has this characteristic. As for the minerals that make up the rocks, and the gases in the atmosphere, they exist only in one form of matter. Secondly, water allows light to pass through it (is transparent to light), not only as a liquid, but also as a vapour and as a solid (ice). If liquid water or water vapour in the atmosphere absorbed light, then photosynthesis would not be possible.

Thirdly, water exhibits very unusually high melting and boiling points. This means that water has a dramatic influence on the climate. The energy required to evaporate water, means that there is a lot less energy available to heat up the atmosphere. This has a pleasant cooling effect in summer. In addition, the freezing of water releases a lot of energy which has a warming effect on cold temperatures. Bodies of water and clouds have a definite moderating effect on climate: cooler in summer and warmer in winter. What’s not to like? In addition, water is a very fluid liquid and it flows very readily. These features contribute to the hydrologic cycle of evaporation. Without the hydrologic cycle, the entire land surface of Earth would be a lifeless desert.

Hydrologic cycle

The volume of water in the biosphere stays basically the same although the amounts found in any one phase can vary. There may be more snow and ice in some areas, for example. One feature that contributes to a moister climate is the plants. Plant leaves open pores in their surfaces to take in carbon dioxide which is essential for photosynthesis. At the same time, water evaporates from the cells in the leaf and escapes into the air. This process consumes a lot of energy and contributes to a cooler atmosphere. Forests have a particularly strong effect on climate, but even grasslands have their impact. The results of evaporation from plants and from bodies of water all contribute to the load of water vapour in the air.

It is the Sun’s energy in the form of heat that drives the hydrologic cycle. As more water vapour builds up in the air, it condenses into clouds. Warming air currents move clouds along. Eventually clouds release their watery burden as rain which moistens the ground, providing water for plants. Excess water runs into rivers, lakes and the sea. From all of these the process of evaporation begins again.

Biosphere summary

We have seen that the biosphere is the platform within and upon which organisms carry out their life activities. The components of the biosphere: rocks, water and air are perfectly designed to be life supporting. Other compositions or characteristics of these components would not allow for life to exist. God made our world perfectly to support living creatures in all their variety.