The Birth of the Earth
About 4.5 billion years ago, the earth was formed from the left over debris of our solar system collapsing under gravity as a hot molten fire ball. As the collapse of its own mass increased due to gravity, the friction in the pack of its mass produced tremendous heat and pressure in the middle of its crust. Both gravity and intense pressure in the centre of the earth came to equilibrium shaping the new born planet as nearly as a spherical ball. Millions of degrees of surface temperature gradually radiated into the vast cold dark space and the sphere solidified forming uneven surfaces like mountains, valleys and other land structures due to volcanic activity. Due to its mass , the gravity is enough to hold the atmosphere around the planet up to 10,000 KM from its surface. Fortunately , the atmosphere contained basic elements like C, H, O, S, N, P due to eruptions of volcanic activity and out of which the building blocks of life were formed. Its distance from the Sun, 93 million miles, was just right far enough for process of cooling and condensation and yet close enough to prevent the gasses from freezing. After gradual cooling for half a billion years, the steam in the atmosphere condensed, rains fell for thousands of years and water gathered to form beautiful oceans. During this long and gradual cooling, Carbon formed enormous variety of compounds with Hydrogen, Oxygen, Nitrogen, Phosphorous and Sulphur which are abundantly found in every life form on this earth. Finally, the conditions on the earth were favourable for the birth of life !
The Design of life on the Earth
One of the important feature of life is that it changes rapidly. Every living creature is born, grows, becomes old and eventually dies. From birth to death , many changes takes place both internal and external for an organism. Any physical system can change with time only when it is not in equilibrium with its surroundings. So every life form is essentially embedded in a non-equilibrium system. Because life exists in non-equilibrium state with its surroundings , it interacts and exchange some of its energy or matter in to its surroundings and take some of the essentials from the surroundings. This way life constantly changes , adopts in the environment and even changes the environment surrounding it. The whole process of exchange and interaction is bi-directional and the concept of evolution , formerly viewed as Natural Selection , is to be expanded and the concept of co-evolution is to be highlighted in understanding the system of life on the earth. The non-equilibrium state is essential for life to evolve and grow and that ‘non-equilibrium’ conditions are constantly maintained around the earth mainly by the Sun. Sun emits light and heat through out solar system and the earth with its life on the surface and the atmosphere around it constantly interacts by absorption and emission of light, heat and matter with other parts of our solar system. In this process, every living creature also interacts with its local surroundings and indirectly with whole solar system itself. This way, the machine of life runs until the internal mechanism cooperates for thorough interaction and finally dies. Hence there is a feedback connection between external world and every creature and also among its various organs. This interaction is not a mere process but a process involved with material and energy transfer. Every creature takes air, food from this nature and by combustion, energy is liberated in each cell of the living organism. With this energy every creature again reacts with the nature performing various life activities and leaving out waste products. Thus there is an exchange of matter and energy from each cell of the body in the process of interaction. Hence the interactions of the living creature with the nature are accompanied in non-equilibrium environmental conditions with properly connected feedback system. Further, this feedback is positive but not negative, because in nature only systems involving positive feed back interactions move far from equilibrium states with a sign of growth or drastic changes which are also the predominant characteristics of life and evolution of living creatures on this earth. But if we observe, growth in every creature is accompanied in this interaction process by its own. That is every creature is self making, an auto-poetic system, it can make its own components of the body through interactions involving exchange of matter and energy with nature. Every creature is duplicating its first cell by its own and again these cells are divided and group of cells thus formed are becoming tissues, and various tissues are developing into organs and various organs into whole body with inherent defensive mechanisms and excellent adaptability features to minute disturbances in the nature. Further, the interactions by living creature with the nature are of non linear type. That is, there is no definite possible reaction for a definite action. We cannot predict the reaction in living creatures. For example if we kick a ball with a certain force we can predict its motion with definiteness as per physics laws framing linear equations but if we kick a dog with some force, we are not definite about its reaction, it may run or it may even bite us. The non predictability is one of the important characteristic of non linear interactions and the same is also observed in living beings also. Another remarkable feature is that each cell of a living creature exchanges its matter with surroundings but still it never looses its structure. Such structures are called dissipative structures. They will have definite form and exist with a boundary separating its environment and to your surprise its boundary is also made by its own components by itself! The same is the case with every living cell, organ and the whole creature. Hence, the living creature can be modelled as an auto-poetic system having continuous positive feedback nonlinear interactive process with its environment and among its components, involving the exchange of matter and energy under non equilibrium environmental conditions with dissipative structural mechanism; and life is the emergent property of such a system.
The Origin of Life on the Earth
About 3.5 billion years ago, the first forms of life started on the earth. The variety of carbon compounds, with the property of chemical affinity, combined together and formed loop like structures. These loops again combined rapidly to cyclic and hyper- cyclic formations through catalytic reactions and soon formed dissipative structures. These structures contained complex catalytic webs with a strong capability of self organisation and even self-replication. This is the pre biotic stage of the evolution. These dissipative structures formed boundaries with their local surroundings due to variation of concentration matter in local regions and these boundaries were later formed as membranes. Perhaps, many dissipative structures might have evolved for a while and then disappeared before first cells are formed. Lynn Margulis, an American Biologist, speculated that ‘ Many dissipative structures , long chains of different chemical reactions, must have evolved , reacted, and broken down before the elegant double helix of our ultimate ancestor formed and replicated with high fidelity.’ In such conditions, the first auto-poetic bacterial cells were born and evolution of life began.
The first cells faced harsh sun light, meteoritic impacts, floods etc. and in each crisis patches of life on the planet would have disappeared in facing these hostile natural forces. But , the ability to self replicate faithfully and with extreme speed, the bacteria again and again faced the challenges and gradually adopted different strategies and finally expanded first in waters and then on the surfaces of sediments, rocks and soil. The most important task that bacteria evolved for its survival is invention of variety of metabolic pathways foe extracting food and energy from environment. One of such process is Fermentation – the break down of sugars and conversion into ATP molecules , the energy carriers that fuel all cellular process and produced Carbon dioxide and methane as waste products. Another important process is Photosynthesis (different from present day plant photosynthesis)- they used hydrogen sulphide in the atmosphere ( erupted from volcanic activity on the earth ) as source of Hydrogen ( the bonds in water are strong than in Hydrogen sulphide and hence the early bacteria chosen the later for Hydrogen ) combined with sunlight and Carbon dioxide from the air to form organic compounds , and never produced oxygen. Further, to escape burning from the ultra violet radiation from the sun light , numerous sensing systems and movements were evolved in the course of time. Some bacteria migrated into deep water, some developed pigments to absorb the harmful rays. In addition to these protective filtering, they developed inherently repairing techniques to the radiation damaged DNA and evolving special enzymes for that purpose. Instead of using their own DNA, bacteria adopted technique of borrowing DNA fragments from their neighbours, This technique gradually evolved into gene trading am0ong bacteria. Large assemblies of such bacterial teams cooperated each other and performed tasks that non of them can do individually. Thus by the first billion years after emergence of life, the earth was filled with bacteria. In fact, many of the bacteria living in early age of the birth of life on the earth have survived essentially unchanged to this day ! The step towards higher forms of life was achieved by forming nucleated cells and highly specialised cell structures through symbiosis. A new concept called Symbiosis is found to be giving promising account for the vast biodiversity. Symbiosis means two living minute creatures jointly depending upon each other for sufficiently longer periods to perform their various functions effectively resulting in a new living structure. The best example is that the mitochondria, the power house of the living cell, is once an independent bacterial type living creature. It joined with primitive living cell long back in evolution and turned into important organelle of the cell, thus resulting in a new cellular structure. Thus the reason for the vast biodiversity is not the competition among species, as Darwin suggested but it is cooperation a t minute levels of life resulted in variety species on this earth. Thus the modern concepts of evolution centred on ‘cooperation’ but not on ‘competition’. The evolution of plants and animals kingdoms proceeded through a succession of symbioses with specialized techniques of cell division basing on the reproductive strategies and genetic material exchange for better survival. Finally, the web of life was unfolded and made the planet earth , a special place in this universe.
The Crisis and the Escape
In the above discussion, one of the interesting and new thought is the shift in understanding the concept of evolution from ‘competition’ centred to ‘cooperation’ centred. The constant interaction with the Nature not only changed the organism but also changed the Nature in which it lives. A new theory called GAIA theory was developed and is named after the Greek goddess Gaia, in the 1970s.
Gaia hypotheses suggest that organisms co-evolve with their environment: that is, they “influence their abiotic environment, and that environment in turn influences the biota by Darwinian Process”.
This concept answered many questions regarding the crisis faced by organisms during the evolution and how their adaptability is achieved by effecting the environment around them. Some of these important and crisis and escapes passed during the evolution are discussed below.
During the early ages of bacteria , due to photosynthesis, the continues absorption of carbon dioxide would have depleted the entire carbon dioxide from the atmosphere and due lack of this green house gas in the atmosphere, and the sun was less luminous than now, temperatures would have fallen making the bacteria frozen to death. However, the depletion of carbon dioxide in the atmosphere was compensated by the process of fermentation adopted by the bacteria in which carbon dioxide and methane were produced. In this way both Photosynthesis and Fermentation became two mutually balancing processes of early GAIA system.
Similarly, in the early ages of bacteria, as Iron and other chemical elements react with water, hydrogen gas was released and rose up through the atmosphere and broke down into hydrogen atoms. Since these atoms are too light to be held by gravity, all the hydrogen would have escaped and billion years later the oceans on the earth would have disappeared. But, fortunately some life forms were evolved at later stage, adopted photosynthesis and emitted free oxygen into the atmosphere. This free oxygen combined with rising hydrogen gas and formed water molecules in the atmosphere, thus keeping the planet moist and prevent its oceans from evaporation.
As the bacteria web expanded rapidly on the earth, bacteria like blue-green algae produced free oxygen into the atmosphere by extracting hydrogen from water by using sunlight. They took the Hydrogen from water for building sugars and other carbohydrates and emitted free oxygen into the atmosphere through ‘oxygenic photosynthesis’. As the algae expanded on the earth, free oxygen levels in the atmosphere were increased. But free oxygen is toxic and extremely reactive with other atmospheric gasses. There were enough metals like iron and sulphur compounds from volcanic activity and these metals observed the oxygen in the atmosphere. But, soon they were saturated and oxygen pollution in the atmosphere resulted in wiping out many forms of bacteria. At this stage, the oxygen crisis was checked by blue-green algae by developing spectacular invention called respiration. The generation of free oxygen in the atmosphere was compensated by its absorption through respiration. The process of respiration happened to be very successful adaptive strategy by the living organisms to maintain the balanced proportion of oxygen in the atmosphere, eventually stabilised at twenty one per cent. If it dropped to below fifteen per cent, nothing would burn and organisms could not breathe . If the oxygen is above twenty five per cent, every thing would burn spontaneously on this planet. Gaia has kept the right levels of oxygen in the atmosphere which is comfortable for all plants and animals for millions of years.
With the oxygen in the atmosphere, ozone layer gradually built up and protected the Earth from the Sun’s harsh ultra violet radiation. Eventually, the evolution progressed and larger forms of life like fungi, plants and animals etc. came into existence on this planet.
This is how life began on this beautiful Earth !!!