Since the beginning of recorded history, humans have tried to foretell the end of the world. In the Bible, it was said that there would be an Apocalypse that would bring about the sudden and ultimate fate of life on Earth. In The Life and Death of Planet Earth, Ward and Brownlee chronicle the last episodes of life from modern mammals to basic bacteria to the fate of Earth itself. They do not aim to instill in the reader a sense of inevitable doom, but rather an appreciation of life as a wondrous machine that is sustained by countless factors in constant equilibrium with each other. They seek to show the consequences if one of those factors becomes unbalanced. They urge us to understand the fate of the world because it already has a terminal illness. We may not have caused the disease, but we are certainly making it worse, like an “old-age patient who smokes many packs of cigarettes per day – and we humans are the cigarettes” (47).
The complexity of life is a dynamic thing. It rises from primitive heat-loving bacteria to plant life to mammals, the most sophisticated product of evolution. But how does one know for certain that mammals will necessarily be the superlative life forms on Earth? Ward and Brownlee believe that biological complexity has already peaked. The young Earth was certainly unlike the present day Earth. Although the sun was much dimmer in the past, high levels of carbon dioxide facilitated a strong greenhouse effect that trapped sunlight and baked the Earth. During this time, colonies of prokaryotic cells called stromatolites were able to tolerate the intense sunlight and photosynthesize. Though stromatolites are rare in present day Earth, the authors foreshadow their return as Earth has already begun to degrade into the hot and humid state that once allowed thermophiles to thrive.
Human civilization has had the fortune of developing in a relatively warm period of about 12,000 years between glacial cycles that occur roughly once every 100,000 years. The Earth isn’t in dire straits yet, but it will “catch a huge cold” in the future (69). Ward and Brownlee comment on global warming at the present from a geological point of view. They take the effects of global warming as a “brief interlude” that will only delay the coming Ice Age by a few centuries, only a blink in time for our planet (73). Other scientists predict that global warming may disrupt atmospheric and oceanic circulation, which can actually speed up the coming of the Ice Ages.
The authors provide an interesting depiction of a future ice-covered city, describing a gray sky overlooking a frozen Seattle landscape. They tell us to look up at the ashen sky and wonder what life would be like during this time. Runoff from hills containing carbon dioxide has fallen to the bottom of the ocean, where it is trapped in a “reservoir” until tectonic plates push these areas above sea level, where weathering releases the carbon dioxide back in to the air in a beautiful geological cycle. Less carbon dioxide means fewer greenhouse gases, which in turn, means less heating and lower global temperatures. The world is also much drier, disrupting agriculture and food supply. The available food supply would only be able to sustain 1 out of every 23 people. This spells catastrophe for the future humans, who may resort to warfare to settle the scarcity of food and shelter. If we do survive the Ice Age, however, we may live to see the gradual shutdown of the carbon dioxide cycle, one of Earth’s primary life-sustaining systems.
Two hundred million years from now, the planet will be in steady decline. Ward and Brownlee take us to a sweltering era in which North and South America have collided with Europe and Africa to form a supercontinent while Australia and Antarctica have drifted northward. Humidity at mid to low latitudes is nearly 100 percent and the average temperature is over 38 degrees Celsius; it resembles the same Mesozoic landscape 250 million years ago. The rising temperatures are caused by the new position of the continents, which causes the formation of new volcanoes and mountain chains. The melting of the former ice sheets in Antarctica raise the ocean levels by 300 feet, disrupting ocean currents and possibly the carbon cycle as well. When carbon dioxide levels become low enough, terrestrial plants, which normally require 150 ppm of carbon dioxide to perform photosynthesis, will suffocate. Though masses of cyanobacteria and algae in the oceans will still thrive, productivity and biodiversity will decrease. Plummeting oxygen levels will strain evolution to its limits as animals must adapt to the increasingly hostile conditions of Earth.
With the extinction of plant life, oxygen levels will fall drastically as skyrocketing carbon dioxide levels trap more radiation from the sun. Ward and Brownlee effectively integrate the explanation of rising temperatures and falling biodiversity with a delineation of a Cambrian beach in order to describe the conditions of the world half a billion years from now. Their dynamic writing style is helpful in visualizing this world as they simultaneously explain the scientific background of their descriptions. They explain that observing the past is useful for seeing into the future, much like how a cannonball rises, peaks, and falls. The rise of the cannonball from a barren, rocky world to an age of animals is inevitably followed by a descent back to the same barren, rocky world. As the Sun becomes brighter, global temperatures will increase. Life will revert back to its most basic origins and although human beings represent the height of biological complexity, stromatolites will make the last stand for life on Earth. When temperatures approach 45 degrees Celsius, the temperature at which mitochondria cease to function, the remaining organisms on land will be forced to migrate to the poles. At 50 to 60 degrees Celsius, mass extinction occurs and only microscopic life is left. At 70 degrees Celsius, only bacteria remain and the oceans begin to evaporate.
Temperatures will continue to rise as the surface of our world begins to cook and the oceans evaporate faster and faster. The rate at which the oceans evaporate will be very important in determining how long life can remain on the planet. If water vapor leaves too slowly, then there will be a deadly moist greenhouse effect: water vapor in the atmosphere will trap sunlight to raise temperatures high enough to melt the surface. If the oceans evaporate quickly enough, perhaps life can linger for another six billion years. If our planet had no atmosphere and thus, no greenhouse gases, temperatures would only rise about 30 degrees Celsius in temperature over the next six billion years. As the Sun depletes its fuel, it increases in diameter to become a red giant. The Sun will take up almost all of the daytime sky. Temperatures will eventually climb high enough to melt mountains; no life would exist at this point. Although current models show that the expanding Sun would eventually engulf the Earth, details are not clear enough to determine the true fate of our world. Since the Sun loses about half its mass during its expansion as a red giant, the Earth would move further away from the Sun due to lower gravitational pull, perhaps enough to narrowly escape the hungry Sun.
It would seem anticlimactic for the Earth to end in such a gradual demise. Humans just cannot comprehend the scope of time required for geological and astronomic processes to occur. As a result, we have dreamed up scenarios that may end the world in a split second. Nuclear bombs, asteroids, and gamma ray bursts are all possible endpoints for life on Earth. But just how likely are these scenarios to happen? There is abundant evidence that an asteroid wiped out the dinosaurs around 65 million years ago, and in 1995, a comet 40 kilometers in diameter crossed the orbit of Earth. Had it collided with our planet, a majority of life would have been wiped out. Eventually, the Earth will become uninhabitable for humans no matter what we do, forcing us to look for new planets and moons to inhabit. But where would we go? According to Ward and Brownlee, Mars, the most popular candidate, is too inhospitable for humans due to the lack of oxygen, its distance from Earth, and the difficulty of terraforming (altering atmosphere, temperature, and ecology to match those of Earth). Some have suggested that we use near-misses from comets to nudge the Earth further away from the Sun, to compensate for its increasing diameter. But this method may be more impractical than terraforming Mars. What about extrasolar planets? Ward and Brownlee say this is “totally beyond the ability of known technology” (207). Even if one could arrive at the nearest star within the human life span with scant amounts of food, water, and air, stopping near a target star would be extremely difficult.
We may not be able to travel to other stellar systems any time soon, but we should feel blessed for our luck so far. Our sun is large enough to give off sufficient energy to support living organisms and small enough that evolution has time to create sophisticated life forms. The world will inevitably end, as will the universe, but Ward and Brownlee are optimistic. They hope that we may learn to take better care of the atmosphere and oceans because they are all part of the biological cycles that run the planet. By spelling out the past and the future, the authors effectively point out just how precious the present really is. As for the future, there is one factor that Ward and Brownlee did not discuss in the text that could significantly affect the survival of mankind: technology. Although the authors dismiss the fantastic escapes from Earth as only science fiction, they admit that they do not have the foresight to predict humans’ ingenuity and intellectual persistence. They have a hunch that although limited in number, human beings may be the last animals on Earth to reach extinction. They hope that their book will encourage research on the long-term future of our species so that we may occupy more than just a tiny fraction of Earth’s timeline.
Book Review:
The Life and Death of Planet Earth
Peter D. Ward and Donald Brownlee
213 pages. Time Books, 2002.