_Light and Life_ by Michael Gross is a brief overview of a variety of instances in which light - from the Sun and other sources - and life on Earth have interacted. A rather short book - not counting the suggestions for further reading it, is 149 pages - I found it an enjoyable, quick read. Though at times it got a bit technical, for the most part it was accessible and interesting.
After a brief preface describing some very general observations as to why light is important in understanding life on Earth and as to why the author decided to explore this topic, the author divided the book into six chapters, each with a different focus.
The first chapter really dealt with astronomy rather than with biology. In this section Gross explored the Big Bang, the origins of stars, the formation of the solar system, and the structure and functioning of the Sun. I found this chapter pretty general, mostly things I had read before, though a good overview. I did find his discussion of the left over radiation from the early universe, the cosmic microwave background, or CMB, interesting. Though its existence was predicted in 1948 by physicist George Gamow, it was only discovered 17 years later by accident, when Arno Penzias and Robert Wilson at Bell Laboratories were trying to determine the source of the excessive background radiation picked up by a microwave antenna that they had designed to receive satellite transmissions. A two-page discussion on neutrinos, while a bit off-topic, was also quite interesting, where the reader will learn about the massive devices built underground in attempts to observe these elusive and extremely difficult to detect particles that come from our Sun and other stars.
The second chapter was much more in line with the book's title, dealing with photosynthesis, including its evolution, the effects it has had on the geology, climate, and evolution of life on this planet, and how it is accomplished at the chemical level (this latter subject did get a bit technical but there were some helpful diagrams). Also discussed is the ozone layer, its formation, its importance to life, and the threats posed to it by pollution (with some discussion as to why certain pollutants interact with ozone).
Chapter three was quite interesting, veering away from the Sun and Sun-related topics, focusing instead on the world of bioluminescent organisms. One interesting point he made, when discussing ecosystems that form around hydrothermal vents, seemingly independent of the Sun, is that ultimately they still benefit from photosynthesis due to their reliance on oxygen, which is present in usable quantities thanks to the activities of photosynthetic organisms.
Gross made many interesting observations about bioluminescence. It is found in a rather diverse group of organisms with little apparent rhyme or reason. It is fairly common in the ocean, virtually absent in freshwater. Various groups of worms and insects can glow, but no spiders. Among vertebrates, only fish use it. There appears to be 30 non-related bioluminescent systems in nature, possibly meaning 30 separate incidents of independent evolution. Gross discussed the idea put forth by William D. McElroy and H. H. Seliger that originally the first such system did not evolve to produce light but rather to detoxify the oxygen that was introduced into the atmosphere by cyanobacteria (as most bioluminescent systems use oxygen). Later on, mitochondria were able to use and dispose of the oxygen much more effectively.
The book explored how light is produced in organisms and its many possible uses, including seeing, sexual signaling, alarm signals, bait, to deceive predators, and, what was interesting to me, "no use." Sometimes light appears to be an unwanted byproduct or at least produced for little understood reasons, such as is the case with luminescent fungi.
The many uses of bioluminescence by humans were explored. One interesting use related to detecting landmines; all landmines leak small quantities of TNT; researchers have developed a strain of bacteria (one that naturally feeds on this chemical) so that it would glow under a UV lamp.
Chapter four explored biological clocks and movement guided by light, including photokinesis (light causing increased activity), phototaxis (light being an attractive signal to which an organism will run towards, phototaxis affecting both orientation and displacement of an organism), and phototropism (as when a plant grows or bends towards light). Also discussed in this chapter was the importance of sunlight to human health physically and psychologically. Interesting was a discussion as why peoples native to the tropics have darker skin; it has nothing to do with skin cancer, which only develops late in life, well beyond their reproductive age. Rather, it has to do with vitamin D synthesis (dark skin and low light would make for problems) and the destruction of folic acid (less often damaged in dark skinned people).
Chapter five was quite interesting, dealing with the evolution and structure of eyes in the animal kingdom, though largely focusing on the human eye. I learned many things I did not know, including about why cataracts form, color blindness (first systematically analyzed by an individual who suffered from it, John Dalton, more famous for the modern concept of the atom), saccades and trans-saccadic memory (saccades are rapid eye movements performed unaware to us up to three times a second, and the trans-saccadic memory creates continuity between images before and after a saccade, though studies have shown very interestingly that this memory is more schematic than detail-oriented; fascinating reading), and binocular rivalry (what happens when the eyes are presented with two separate, incompatible images, resulting not in a blending of the images or two images but rather an alteration of two competing images at apparently random time intervals, though this is to some extent influenced by conscious thought).
The final chapter was one of the briefest, providing some highlights of Sun worship through the ages and past thinking about light and vision. We've come a long way from the ancient Greek philosopher Empedocles' idea of "vision rays."
