S13-THE GREAT IMPORTANCE OF PHOTOSYNTHESIS

 

By PragyanSharma Polavarapu

Scientists say that it might have taken earth a few hundred million years to cool–after its formation about 4500 million years ago (from a hot sphere of molten rock and molten metal) . Scientists say that as earth further cooled water till then held in kilometer-thick clouds rained continuously for centuries with occurrence of big dazzling lightning and the oceans formed. This was perhaps the situation about 3000 million to 4000 million years ago.

Scientists examined oldest rocks in western Australia and estimated their age with help of radioisotope technology and also identified some fossils which were billions of years old . They say that about 3000 million years ago the temperature of the oceans cooled to around 30 to 40 degrees centigrade and that there were many sulphur-spewing active volcanoes. Some bacteria managed to live feeding on the sulphur-based compounds and even in waters near hot springs . There was absolutely no oxygen in the air and there were no green grass meadows on the stony land .

THE CHANGING ATMOSPHERE

Scientists say that in the oldest atmosphere of earth 4500 billion years ago there were only helium and hydrogen just as at similar places and similar situations in the universe near stars. There was no oxygen in the air surrounding earth.This was the first atmosphere of earth .

The planet earth was extremely hot and in a molten state with even the rocks in a molten state.We should understand that the earth moved more than a hundred and fifty million kilometers away from the sun during the process of its formation and entered a solar orbit at that distance. The earth started to cool along with other planets and their satellites but the cooling process perhaps took a few hundred million years!

The earth and planets now entered an extremely cold space in the all pervading emptiness of cosmic space . In this extremely cold environment of perhaps “minus 150” or “minus 200” degrees centigrade temperature earth began to slowly solidify. Thousands of kilometers thick semi-solid stony plates of continent-size ( thousands of miles long and thousands of miles wide ) were forming around the hot metallic core of earth . Not just this. Above these huge soft semisolid stone plates a solid stone crust of 20 or 30 miles thickness formed. Scientists say that first rains fell about 3000 million years ago . Before that time the earth being very hot all water hung in kilometers- thick clouds and that the temperature was around 70 to 80 degrees. It might have rained for hundreds of years and the oceans were filled. There were thousands of volcanoes . Volatile gases evolved in unlimited quantities sending out pungent smelling vapours . The vapours contained billions of tons of H2O, CO2, CO,ammonia, nitrogen, sulphur oxides etc .This pungent and suffocating atmosphere—(suffocating for us humans)– is called second atmosphere. It can be said that that such atmosphere might have existed for about three billion years. There was no oxygen at all.

Scientists say that by about 2700 million years back— (after millions of years of rains and cooling of the stone layers of the earth and perhaps also due to the slow cooling in the liquid metallic deep interior of earth) — the temperatures on earth’s surface and in oceans cooled further down to 30 to 40 degrees . Everywhere there were volcanoes spewing sulphurous gases, carbon dioxide, water vapor and hydrocarbons and ammonia.

As already said, over hundreds of millions of years— due to temperature adjustment and due to formation of world’s oceans and the torrential rains —the weather cooled .Scientists say that single-celled organisms without any nucleus and any recognizable body shape and body parts might have appeared in the oceans and seas even in those far away “thousands of millions of years”. All those creatures lived only in water.

SOURCE OF WATER ON PLANET EARTH

Scientists have also studied the question—where from did the huge quantity of water that accumulated in oceans come? Some water might have come through the ices brought by thousands of meteors and comets coming from millions of miles and flying by very near to earth or crashing on earth. However from the large number of ancient volcanoes limitless quantities of water vapor might have come originating from the deep stony interior of earth. Scientists remind that there were limitless quantities of hydrogen in atmosphere existing since the start of time –from the time of formation of planets . Scientists say that in the gases surrounding the primordial molten earth, oxygen might also have been abundant.If there was abundant hydrogen and oxygen in air it may be possible lot of water might have formed in earth’s atmosphere in the presence of incessant electrical energy of the lightnings in the clouds . The temperature of ocean water at the time (when the first oceans formed) might have been high at 70 to 80 degrees centigrade and there was no free oxygen. In the atmosphere there were also abundant quantities of inert gas nitrogen ,carbon dioxide and carbon monoxide and some hydrocarbons. The average depth of ocean might have been 3.7 kilometers as per scientific opinion about such colossal quanties of H2O.

THE BLEAK WORLD

Now a most surprising fact may be mentioned here. Since in the beginning there was no free oxygen in atmosphere and oxygen was available only in a dissolved condition in water no creatures could live on land . All living beings lived only in water in the oceans. All living creatures were also microscopic in size and only lived in kilometers-long and kilometers-wide floating colonies on the surface of the oceans. The winds and storms and ocean currents carried them in every direction. The microscopic living creatures breathed only the oxygen dissolved in water.

The floating and living creatures were extremely small —of microscopic size or at most a millimeter size. They were all “single celled creatures”. There was no oxygen at all in the air. The plant kingdom was not yet born on earth at that time. There was no green plant ,no trees,no grass. All land was only lifeless stone where there was no greenery as we now know and there was not even one four-legged living creature !

The microscopic size or millimeter size living creature had no bones in body , no thinking mechanism, no nerve system in body to feel pain etc, no eyes, no ears etc. The little microscopic and millimeter size creatures only floated in the water. When hungry -they simply devoured the neighboring creature. They devoured each other .

In short ,to recollect again—there was no oxygen ,there were no green plants, no green grasses, no green trees, even no green mosses, no lions, no deer and rabbits and birds! The great reason is that there was no plant kingdom to manufacture the carbohydrate molecules in nature’s factories called “plant leaves”!

THE GREAT REVOLUTION CALLED PHOTOSYNTHESIS

There was soon a great change. We may call it a revolution . Some green bacteria (the cyanobacteria) existing in water 2.3 billion years ago started to produce carbohydrate in their bodies . The carbohydrates were tiny food material that could be consumed as food by other living beings. Till then all the microorganisms devoured each other when they were hungry. The cyanobacteria started the new “photosynthesis” reaction to produce carbohydrate, perhaps as tiny particulate food material in their bodies.

It is most interesting for modern school students to note— that the cyano-bacteria just used carbon dioxide gas and water vapor and sunlight to synthesize in their bodies the carbohydrate particles —which became the primary food of “universe”. Whether the carnivores or herbivores –all have to depend on the carbohydrate for their existence.

But most importantly— from the view point of all living creatures including humans which appeared only two billions years later—a wonderful thing also started to happen and continued for ever during all these billions of years. The green bacteria which perhaps lived in kilometers- long floating colonies in oceans enjoying sunlight released oxygen every second every day for two thousand million years and lo the entire air was filled with oxygen. In addition to the food particles called carbohydrate which became the basic food of the universe the life giving oxygen gas filled the air . Living beings till then living only in ocean waters spread also to the stony land and after hundreds of millions of years the green tree cover(billions and billions of small and big trees, the creepers,the greeses and mosses ) filled every inch of the earth as the cool skies rained water . Not only the giant forest trees but also the hundreds of billions of leaves of plants and the hundreds of billions of green blades of grass in the millions of acres of land took over the duty of photosynthesis from the tiny bacteria and lessened its burden. The planet earth entirely underwent a change.