The Equations of Life by Charles S. Cockell

The Equations of Life by Charles S. Cockell

Author:Charles S. Cockell
Language: eng
Format: epub
Publisher: Basic Books
Published: 2018-06-19T04:00:00+00:00

where e is a mathematical constant, Ea is the activation energy, R is the universal gas constant, and T is the temperature of interest. The more unusual factor, A, is a constant for each chemical reaction; it defines the frequency of collisions having the correct orientation.

What does this exponential relationship between temperature and the reaction rate mean for life?

Consider a reaction with an activation energy of 50,000 joules, which is the energy needed to get the reaction going. Drop the temperature of the environment from 100°C to 0°C, and the reaction rate decreases by just over 350 times. However, drop the temperature by another hundred degrees, from 0°C to −100°C, and the reaction rate decreases by a staggering 350,000 times! At the temperature of liquid nitrogen (about −195°C), the rates of reaction are 1023 (100,000 billion billion) times less!

The optimistic might immediately hit back with the rejoinder that catalysts could accelerate reaction rates, but even the best enzymes and chemical catalysts increase reaction rates by only a few orders of magnitude. This exponential relationship may not be a problem: life can merely operate at these slower rates, maybe replicating many times less frequently than typical Earth life. However, in most planetary environments, life is subjected to constant damage that must be repaired. One source of this damage is background radiation.

Thus, life is confronted by a problem. It must be able to repair radiation damage to prevent the damage from accumulating to fatal levels. In the deep subsurface of Earth, where there is little energy available to grow and reproduce, microbes might divide very infrequently. And yet even here, they must get enough energy to repair damage from radiation. In the Earth’s rocks, natural background radiation would kill the most radiation-resistant microbes known after about forty million years if they remained dormant. On Mars, as the atmosphere is thinner than Earth’s, the surface has the additional problem of higher levels of cosmic radiation. Here, even a radiation-resistant dormant microbe, if such a thing ever existed there or is accidently dropped there by human or robotic explorers, would be killed within thousands of years, or much less.

If the chemical reaction rates in the cold-temperature life form are many thousands, millions, or trillions times less than those in the life we are familiar with, it is likely that this cold life form will accumulate a great deal of damage and be unable to repair itself sufficiently fast to remain alive.

There may, however, be some more optimistic news for the low-temperature life form. Some challenges it faces depend on temperature. The formation of reactive oxygen species, the decay of amino acids, and the thermally caused decay of DNA base pairs depend on temperature: the lower the temperature, the slower the damage occurs. Although the low-temperature life form may well incur damage, some of this degeneration will be correspondingly slow, partly making up for the slow rate at which it can repair itself. However, direct damage to molecules caused by radiation can be essentially independent of temperature.



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