“Rare Earth” is a classic read, a book to begin with before exploring other publications on astrobiology. Astrobiology, the study of life in the universe, is a relatively new field and one that has experienced rapid acceleration in the last few decades- much like what occurred in the field of Genetics after the discovery of DNA in the mid 1900s.
The authors define the Rare Earth Hypothesis “the paradox that life may be nearly everywhere but complex life almost nowhere” as one that cannot be tested since it would require space travel to distant stars. Although, by their own admission, they cannot test their hypothesis, the authors go on to cite the following conditions for complex life to exist on Earth:
The Sun needs to produce a stable, consistent level of energy output.
The planet needs to sustain a sufficient level of oxygen for complex life to survive (it is estimated that it took 2 billion years to do this).
The planet needs to be of a specific size, chemical composition, and be positioned a certain distance from the Sun.
Earth needs to have a very low asteroid impact rate (otherwise life would be wiped out).
Earth needs to have a moon of considerable size compared to its own to stabilize its tilt.
Earth needs to have a plate tectonics feature- a key requirement for life. Plate tectonics are a global thermostat and are needed to produce the magnetic field and promote biodiversity on the planet (Earth the only planet in our solar system to have such a feature).
Our solar system’s position and movement in the Milky Way galaxy need to be designed in a way to keep the solar system out of a region with a high comet influx rate.
The solar system needs to be positioned in a region where its movement is mainly within the plane of the galaxy (as opposed to its spiral arms).
The mass of the Milky Way galaxy our solar system lies within is just right- enough to have sufficient metal content to support the existence of complex life.
The planet needs to be shielded from exploding stars- supernovae. Our planet is protected from supernovae by the very fact that there aren’t very many stars in our vicinity. An exploding star has the capacity to exterminate life within a one light-year radius (6 trillion miles).
The authors argue that because simple forms of life can exist in very hostile environments, such as in deep-sea rifts where temperatures can reach 200 degrees Fahrenheit, then simple life can probably exist elsewhere in the universe. They assert that the existence of extremophiles that are adapted to extremely high or extremely low temperatures, or highly acidic, basic, or saline environments, is strong evidence for this notion. The authors also state that “life can exist well above and below the temperature range (32 – 212°F) that allows for the existence of liquid water at a pressure of 1 atmosphere, the conditions found in what has been called the habitable zone.” Thus, they assert, the original concept of what constitutes a zone habitable for life is now obsolete.
There are multiple points in the book where the reader can marvel at the intricacy of the creation of our planet, such as the provision of just the right amount of carbon to sustain life. If our earth happened to be carbon-rich for example, it would likely have a crust comprised of graphite and an interior made of diamond and silicon carbide. The presence of these compounds would not allow for volcanic eruptions or even weathering processes to occur.
The authors go to great lengths to describe the origin of life on the planet referring to a model that asserts that the “cradle of life was clay or pyrite crystals”. They demonstrate why they believe that life may have originated on Earth or that our planet may have been “infected” with life “from elsewhere”. They then attempt to use evolutionary history theories as a basis to model the formation of life forms on other planets.
It was obvious that the authors were not free from the influence of Darwinian ideology when tracing the origin of life, but somehow they achieved their ultimate However, the authors’ premise that the existence of life as we know it was down to the mere involvement of “material, time, and chance events” left me puzzled. What surprised me was that although the authors’ research is teeming with evidence against the earth and solar system existing by mere ‘chance’, the authors do not clearly acknowledge the presence of an All-Wise Creator. They argue that “if some god-like being could be given an opportunity to plan a sequence of events with the express goal of duplicating our “Garden of Eden”, that power would face a formidable task”- outright undermining the power and intelligence of the First Cause. Then again, in their own words, the authors are “like 2-year- olds, just beginning to comprehend the immensity, wonder, and hazards of the wide world.” Unlike 2-year-olds however, the lens through which they see the world might be a little blurry.
In summary, this book is filled with examples of why conditions on our planet need to be just right for complex life to exist. It makes you appreciate the incredible odds of existing as a human being at this point in space and time. In the words of Lewis Thomas,
“Statistically, the probability of any one of us being here is so small that you’d think the mere fact of existing would keep us all in a contented dazzlement of surprise”.
The odds of life emerging purely out of chance and so-called natural forces is not small. It is literally impossible. Indeed, such a claim is an insult to the Creator of life just as it would be to the great engineers and scientists who worked on the International Space Station(ISS) if we claimed that “there is a small chance that we might get a structure like ISS purely out of random collusion of its raw materials.” Any reasonable person would intuitively reject such a claim. Thus, our mere existence in a palace like Planet Earth is something that could never be possible without The Infinite Power to whom we should be eternally grateful.