Pages

Saturday, December 1, 2012

56. Energy is the Real Engine That Drives Evolution



By definition, dynamical systems are those that change or evolve with time. Biological evolution is only a subset of dynamical evolution. If a dynamical system does not receive an input of energy, it decays towards a state of equilibrium, and then stops evolving. Energy is the engine that drives all evolution.
   
The planet we live on is a spaceship, which has been receiving an input of negative-entropy solar energy throughout its existence. Influx of this energy is mainly responsible for keeping our planet in a state away from equilibrium, which is the reason for the ever-rising levels of its complexity. All life-forms on Earth owe their existence and sustenance to this input of energy from the Sun. And the entire ecosphere can be regarded as one single, highly complex, system: SYSTEM EARTH.


In a notable book (Energy: Engine of Evolution), Niele (2005) presented the Earth's historical energy-staircase of increasing complexity. As becomes clear on a perusal of Niele's book, an energy-based evolutionary approach to the history of the Earth provides major insights into our current affairs.

Our energy-emitting Sun came into being ~4.6 billion years ago. The energy it emits in all directions comes from the thermonuclear fusion reactions taking place in it. Some of the energy emitted by the Sun is intercepted by our Earth, and most of it is then emitted back into outer space in due course in a highly degraded form.

Energy has the capacity and tendency to cause change. For the change to occur, the energy has to transform to another quality. According to the second law of thermodynamics, such change entails an overall state of higher disorder or entropy. This dissipation can occur only if there are dissipative paths available. As we shall see presently, such paths are indeed there for the energy available on Earth.

Most of the solar energy received by the atmosphere surrounding the Earth escapes from it ultimately. If this were not so, the average temperature of the Earth would go on rising. What we have instead is a fairly constant average temperature.

The tiny fraction of low-entropy (or high-quality) solar energy retained by the Earth drives processes such as photosynthesis. Some other sources of energy on the Earth are: geothermal energy; cosmic microwave radiation; and the energy released by natural and artificial radioactivity. The energy flow in and around the Earth is influenced by the energy flows in the universe. A delicate balance exists among gravitation, nuclear reactions, and radiation, which moderates this flow of energy.

As analyzed by Niele (2005), there have been FIVE ENERGY REVOLUTIONS since the origin of life on Earth:

1. The photo-energy revolution (emergence of photosynthesis). This occurred ~3.8 billion years ago.

2. The oxo-energy revolution (aerobic respiration). This occurred ~2.1 billion years ago.

3. The pyro-energy revolution (domestication of fire by humankind). This occurred ~0.5 million years ago.

4. The agro-energy revolution. This occurred ~12,000 years ago.

5. The carbo-energy revolution. This occurred ~400 years ago.

Each energy revolution heralded a new dominant ENERGY REGIME: Exposure to a new energy source can herald a new dominant-energy regime, provided a new path for energy dissipation is available.


Shown above is Niele's 'historical energy staircase' for the system Earth, with near-constant influx of low-entropy energy (mainly solar energy). Plotted on the x-axis is time (not to scale). The y-axis depicts schematically the generally increasing degree of (terrestrial) complexity. Niele has identified the various energy revolutions (at times marked t1, t2, etc.), each such revolution heralding the onset of a specific energy regime. For example, the Photoenergy Revolution, which occurred at time t1, marked the emergence of the Phototrophic Energy Regime.

t1 = ~3.8 billion years ago;
t2 = ~2.1 billion years ago;
t3 = ~0.5 million years ago;
t4 = ~12000 years ago; and
t5 = ~400 years ago.

The time t6 is when the next energy revolution will occur, and is a question mark at present. We can only speculate about it. One possible scenario is that t6 will mark the emergence of a Nucleocultural Energy Regime, heralded by a Nuclear-Energy Revolution, but, as I shall discuss in future posts, there are other possibilities also.

Six ecologically dominant energy regimes have been identified by Niele in the history of the Earth. These are:

(i) Thermophilic regime. The corresponding energy period is called the thermion period.

(ii) Phototrophic regime (photian period).

(iii) Aerobic regime (oxian period).

(iv) Pyrocultural regime (pyrian period).

(v) Agrocultural regime (agrian period).

(vi) Carbocultural regime (carbian period).

After human beings appeared on the evolutionary scene, each energy revolution was influenced by a 'cultural trigger' or signal:

For the pyro-energy revolution the trigger was the origin of the human species.

The agro-energy revolution was triggered by the ‘Symbolisational Signal’.

The current carbo-energy revolution was triggered by the ‘Quantificational Signal’.

The next energy revolution of the future may be triggered by the ‘Macroscopical Signal’.

These terms will be explained in future posts, as we take a brief look at each of the energy regimes. Let us begin with the thermophilic energy regime here.

As mentioned in Part 53, life appeared on Earth during the thermophilic regime. It originated through the emergence of heat-loving or thermophile organisms. They were the ecologically dominant organisms in that period; hence the term ‘thermophilic energy regime’ for the energy regime engendered by them. They have been called ‘hyperthermophiles’ because they were ‘hard-nosed heat lovers’.


This energy regime also saw the emergence and establishment of a metabolism mechanism for the supply of energy, with ATP as the principal cellular energy currency (Smil1999). The hyperthermophiles used nucleotides for synthesizing DNA, and amino acids for synthesizing proteins. During this energy regime there was practically no oxygen in the atmosphere of the Earth, although there was plenty of carbon dioxide.


For higher and higher complexity to emerge, there must be an energy gradient from a local energy source to an energy sink, and there must be a energy-dissipating pathway. For the thermophilic energy regime:

Energy source: Primordial heat from the accretion events during the formation of the planet Earth.

Energy sink: The cold atmosphere above the seas.

Energy-dissipating pathways: Chemical evolution, autocatalytic processes/metabolism.

Chief drivers: The hyperthermophiles.