Eventually, the Earth will no longer be fit for human existence. In approximately 5 to 6 billion years the sun will exhaust its hydrogen supply. In the next 10 million years a comet will likely strike Earth, or the planet will be doused in supernova radiation. Within the next 100 thousand to 1 million years an asteroid similar to the one that created the Chicxulub crater and caused a mass extinction event will likely collide with Earth.
Before these extraterrestrial events occur, though, more planetary threats endanger human survival.
From New Orleans to Iceland, Haiti to Indonesia, life on planet Earth suffers from the constant onslaught of extreme weather like hurricanes, tsunamis, and blizzards and geologic events like volcanic activity and Earthquakes.
With all these threats, it may seem like the human species is powerless to change the natural future of the planet. Today, however, we know that is not true. Anthropogenic climate change is having a significant effect on global systems, as indicated by the changing distribution and abundance of native plant and animal species as well as shifts in their phenology. Estimates on the number of species present in 2004 that will go extinct by 2050 as a direct result of climate change range from 15% to 37%, and some changes in biological and physical systems can be attributed directly to human activities, such as land use changes, demographic changes, and pollution. Humans have the ability to make drastic and lasting impacts on the planet, and if humans do not combat the environmental impact they have made so far by re-engineering a safer planet, they may have to look elsewhere for habitation.
With earthly resources rapidly depleting, massive environmental change, and limited space for a growing human population, the utilization of alternative home planets may move from the realm of science fiction to reality.
Terraforming is the process of engineering planets to make them habitable for terrestrial life. This idea was, in fact, born out of fiction. Olaf Stapledon, in his 1930 novel Last and First Men, first described a project undertaken to make Venus suitable for humans which began by placing photosynthetic plants on the surface to release oxygen. In 1942, Jack Williamson coined the term “terraforming” in his short story Collision Orbit. In 1961, Carl Sagan wrote the first academic paper on terraforming and published it in Science.
Traditional conceptions of terraforming include the idea that new habitats would replicate Earth. Because life has evolved alongside Earth, the traditional conception makes intuitive sense. But mankind’s inadvertent altering of the environment makes me believe that our current planet is no longer an ideal habitat for Homo sapiens sapiens.
As evidenced by the overwhelming evidence for anthropogenic climate change (greater than 90% probability), mankind has the power to alter planetary environments. We are currently in the process of reforming the biological environment of our planet, although we are likely making it less suitable for human life. Many contemporary efforts are focused on slowing and repairing the damage that has ensued since the industrial age. In addition, societal pressures to reduce carbon footprints have changed individual lifestyles and affected policy decisions, but these efforts alone will not reduce the greenhouse gas pollution in our atmosphere. In order to re-terraform Earth, we will need to engineer solutions that may eventually prove useful for terraforming other planets.
Naturally residing photosynthetic organisms have taken some of the burden of reducing carbon pollution. As carbon dioxide levels have increased, short-term responses in plants include increased photosynthesis and growth. However, it remains unclear whether natural photosynthetic systems will have a long term effect on the carbon equilibrium because organisms may acclimate to changes in carbon dioxide level.
In order to sequester more carbon annually, reforestation and afforestation (planting trees where they did not previously exist) projects have been proposed. However, natural limitations on the ability of organisms to fix carbon exist, such as a feedback mechanism that limits plant response to increased carbon dioxide and the efficiency of the rate-limiting Rubisco in the Calvin-Benson cycle. Attempts to engineer organisms to circumvent these restrictions have been taken in experimental science laboratories; for example, engineers have tried to create more efficient carbon fixation pathways. Also, bio-char, a biomass-derived charcoal, has been shown to sequester carbon and enrich soils, giving it applications in agriculture.
Earth was not always a Garden of Eden, teaming with life and diversity, though. More than 3.5 billion years ago, the likely microbial ancestor of all life on Earth arose in an environment dominated by carbon dioxide, water vapor, and some nitrogen. The evolution of cyanobacteria instigated Earth’s first mass pollution event more than 2 billion years ago. These microbes, also called blue-green algae, were able to store the carbon in the atmosphere as carbohydrates for an energy source via photosynthesis and released oxygen as a byproduct. This pollution of the atmosphere with oxygen was the first step towards the natural terraforming of Earth, not only because the chemical composition of the atmosphere changed, but also because the global temperature dropped as the greenhouse effect was reduced. Thus, life has had strong influence on Earth environment since its inception, and the environment and life have coevolved since.
The Gaia theory, developed by scientist James Lovelock, extends this coevolution concept and says that the Earth’s components all interact dynamically to produce a homeostasis that maintains an environment conducive to life. Essentially, Lovelock argues that the stability seen in oceanic salinity, surface temperature, and atmospheric composition arises not from statics, but because a global feedback system that includes the hydrosphere, the cryosphere, the lithosphere, and (perhaps most importantly) the biosphere actively sustains these conditions for life. Simulations in Daisyworld supported the Gaia theory. This computer model showed that, while temperature increases linearly with solar intensity in abiotic worlds, a world containing populations of black daisies, which absorb light and trap heat, and white daisies, which reflect light and have a cooling effect, will maintain a constant temperature suitable for daisy growth as solar intensity changes by modulating the proportions of black and white daisies.
Still, hypothesis may have biased the programmers of the Daisyworld simulations because examples which produced the desired results were selected. While some experimental and observational evidence exists to support the Gaia theory, the theory remains very controversial. The “Weak Gaia” theory, which supports coevolution and interaction between the biosphere and the environment, has wide support, but many find the stronger suggestion that the whole Earth is a self-regulating, self-organizing homeostatic system set to optimize conditions to support life an extreme, untestable hypothesis.
The Gaia theory employs the concept of homeostasis in the same way it is used to describe the regulation in organisms. In fact, Lovelock draws a picture of Earth itself as an organism, and names that organism Gaia. He envisions that, like a living organism, Gaia can reproduce by colonizing and terraforming new worlds.1
1The idea of Gaia as an organism is the most controversial topic in the Gaia theory, and Lovelock later modified his language to downplay this idea. Gaia theory supporter Lynn Margulis emphasized that Gaia is not an organism, but an emergent property. Margulis developed the initially controversial endosymbiotic theory, which, now widely accepted, says that eukaryotic cells arose when prokaryotic cells engulfed other prokaryotic cells and they coevolved. As one of Margulis’s students stated, "Gaia is just symbiosis as seen from space."
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