With forest resources--"the lungs of the Earth"-- under attack in many regions, some have raised concerns about the planet's oxygen supply.
Oxygen is the most abundant chemical element, by mass, in our biosphere, air, sea and land. Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium, but mainly in combination with something else. The stuff is all around us but we don’t see it. Chemically joined with other elements it accounts for more than a quarter of Earth’s total weight and almost half the mass of the crust. Free or dissolved molecular oxygen, however, represents only 0.01 percent of the total crust, hydrosphere, atmosphere, and biosphere taken together. Only seven of every billion atoms takes the form of molecular oxygen (O2), plus a neglible quantity as atomic or singlet O and ozone (O3). If the atmosphere contained much more oxygen, it would be inflammable. Remove oxygen and only anaerobic bacteria could survive.
How did plants come to alter the atmosphere? The key is the way in which plants create their own food. They employ photosynthesis, in which they use light energy to synthesize food sugars from carbon dioxide and water. The process releases a waste gas, oxygen. Those of us in the animal kingdom rely on oxygen to metabolize our food, and we in turn exhale carbon dioxide as a waste gas. The plant use this carbon dioxide for more photosynthesis, and so on, in a continuing system.
Oxygenic photosynthesis (synthesis by light) is by far the largest and most familiar source of O2. Upon its introduction at precariously trivial and fluctuating levels perhaps 2.8 aeons ago, oxygen began to play a role in the evolution of life and earth’s surface processes. After that, if not earlier, photosynthetic O2 and perhaps plate tectonism joined sunlight, gravity, and water as lead players on the evolutionary stage. Yet, for another 6 to 8 geocenturies it remained at vanishing low levels as a result of reactions with a variety of reduced substances.
Nor was oxygen-evolving photosynthesis the only source of oxygen. Physical splitting of H2O by photolysis was probably the prevailing initial process. Photolysis of CO2, as well as the release of oxygen from the metallic oxides as a result of microbial processes and chemical weathering, are potential but poorly understood sources.
On reaching present levels, perhaps 4 geocenturies ago, oxygen was still consumed by new reduced volcanic gases, erosionally exhumed carbon, and reduced matter in the hydrosphere right up to the present. Levels fluctuate with rates of erosion volcanism, and deforestation. The indefinite continuity of oxygen is not guaranteed.
Forests, a major source of oxygen to our atmosphere, are very important to the world’s climate because they help in rain formation and absorb carbon dioxide (CO2) from the air. As the forests disappear, the weather will change, and some places will dry up.
There are many benefits that we get from our forests. Some of these include cleaner drinking water, a home for plants and animals, economic growth, clean air, recreational opportunities. Another most important benefit we get from trees is called oxygen. If there were no trees to give us oxygen to breath, we would not be able to live. Trees are known as the oxygen supplier to our planet.
As vast forests such as the Amazon are denuded of their beauty and natural resources, our atmosphere is also seriously altered. The forests are stripped faster than they can be replanted, and when severely depleted, photosynthesis is greatly reduced. No photosynthesis, no oxygen. No oxygen, no life. But deforestation continues at a break neck speed in many areas of the world.
Earlier in Jharkhand forest played major role in balancing the temperature difference. But now forest cover is rapidly depleting. Even one of the biggest forest of Asia popularly known as Saranda Forest is also decreasing many fold due to rampant iron ore mining in Jharkhand State. Today the remaining forest areas are unevenly distributed. Bokaro has only 4.4% of area under forest. Similarly Sahebganj has only 2.31%, Dhanbad 12.72%, Deoghar 9.5% and Ranchi only 23.37% of area under vegetation.
At the Survey and Settlement (1902-1910) the area under forests in the Ranchi districts approximated to about 2,281 square miles, i.e. about 32 percent of the total land area of the district. At the Revisional Survey and Settlement (1927-1935) this area shrank to about 1,956 square mils, i.e. 27 percent of the total land area. Thus during a period of 25 years, 325 square miles of forests had disappeared. When the forests were notified under the Bihar Private Forests Act,1946 and demarcation was done only about 1,065 square miles were found under forests in this district. Adding 213 square miles of reserve forests to this, the total area under forest in this district came to 1,278 square miles. Thus in course of a decade over 600 square miles of forests disappeared. Now it has reached up to 23 percent and gradually decreasing further.
Regarding percentage of oxygen present in the atmosphere in the geological past, it was revealed that air bubbles trapped in fossilized amber had been analyzed and found to contain oxygen levels of 38%. Yet today it is well known that the average content of the oxygen in air is only 19% to 21%. If we believe on the report of oxygen level in the fossilized amber, it appears that since the early history of our earth there has been a stunning decrease of 50% in the average oxygen content of the air we breathe. According to other report, analysis of the air in various parts of the world today reveals the frightening fact that the oxygen content continues to decline. In fact in some of the larger and therefore more polluted cities the oxygen levels have been measured at a disturbing level of 12 to 15%. Scientists claim that anything under 7% oxygen content in the air is too low to support human life, even for short periods.
Historical trends, as explained in Atmospheric Oxygen, Giant Paleozoic Insects and the Evolution of Aerial Locomotor Performance by R. Dudley, JExB, show a high of about 35% just before the beginning of the Permian, with a rapid decline to a low of about 13-14% near the beginning of the Triassic, then a small spike at about 17% in mid Triassic, another drop to about 14-15% early in the Jurassic, a sudden climb to about 21% by mid-Jurassic, then a gentle climb to about 26% early in the Tertiary, and a rather constant, steady decline to the present "20.9%."
Our planet’s future is under threat as cutting back tropical forests we put our supply of oxygen gas at risk.
There is difference in opinion about oxygen depletion. Some scientists believe that our atmosphere is endowed with such an enormous reserve of this gas that even if we were to burn all our fossil reserves, all our trees, and all the organic matter stored in soils, we would use up only a few percent of the available oxygen. No matter how foolishly we treat our environment heritage, we simply don’t have the capacity to put more than a small dent in our oxygen supply.
But we can’t take any risk. If forest or plants provide oxygen, cutting or burning trees is definitely going to affect the oxygen balance of our atmosphere.
Cloud,P. 1988. Oasis in space, earth history from the beginning. W.W. Norton & Company, New York.