If there were ever a case to be made for space exploration, the very real possibility of mass extinction is certainly reasonable. Our planet won’t be around forever. Whether this is a result of our sun dying or some other cataclysmic event (natural or man-made), humanity must find a way to survive beyond our own planet. Let’s consider mass extinctions further as a justification for continued space exploration.
Mass Extinctions Examined
The normal course of evolution sees the eventual rise of new species and the dying off, or extinction, of other species. During relatively quiet periods of earth’s vast history, there is a natural appearance and disappearance of species as some adapt to changing environments and others fail to do so. It should be noted that extinction is just as final as it sounds: Every individual of the species dies off and no descendants are left behind.
That definition is even more striking when applied to mass extinctions. These major events go way beyond the normal ebb and flow of background extinctions. For instance, approximately 250 million years ago a mass extinction event wiped out at least 90 percent of all species of the time. Such a thorough scrubbing out of life can be hard to imagine. What could conceivably trigger it? There are a handful of possible causes of mass extinctions: atmospheric changes, the changing landscape as whole continents move about the planet’s surface, and extraterrestrial object impacts with the earth.
Atmospheric change seems to lack the visceral punch that other cataclysmic events invoke in the imagination. There is no cinematic earth shaking involved. But in a world not yet populated with legs, tails, and teeth, shifts in the atmosphere’s recipe can make sweeping changes. Prokaryotes, simple versions of single-celled life, thrived on primitive earth 3.5 to 2 billion years ago, initially making a good living without oxygen in the atmosphere at levels we are used to today.
Photosynthesis, the ability to convert sunlight into food, then slowly but surely came on the scene. Its increasing use, primarily by cyanobacteria, gradually pumped more and more free oxygen into the oceans. Over time the oxygen then made its way into the atmosphere about 2.7 to 2.2 billion years ago. Oxygen levels shot up and started making a mess of things for other life of the time. It tends to break chemical bonds and thus interfere with enzymes and cell activity. This resulted in the extinction of many of the simple prokaryotic life forms around at that time, making room for the life forms that could adapt to the change. Additionally, the rising levels of oxygen may have sparked global climate change, chilling and glaciating the earth.
Fast-forward through time by a couple billion years and multi-cellular life has finally arrived. Plants, fungi and animals 500 million years ago were, of course, still primitive, but they came a long way from simple aquatic prokaryotes. This advanced life still faced massive challenges to survival, such as the treacherous, moving land itself.
Much of marine life, both now and then, populates shallow waters. About 250 million years ago all of the continents crammed together into one land mass called Pangaea, erasing much of the shallow water habitats and the marine life in them. Extreme volcanic activity of the time also played a role in extinctions. The atmosphere was choked with ash, and carbon dioxide warmed the climate, evening out temperatures around the globe. This could have then stalled the ocean currents since there was little to no water temperature differences to fuel them. As a result, oxygen wasn’t as readily mixed into the water and aquatic life suffered the consequences.
Adding to the troubles, previously separated similar species now shared the same turf on Pangaea, leading to competition and possible extinction of some species. All of these circumstances together may have contributed to the most significant extermination in all of earth’s history: the Permian mass extinction. It impacted marine life especially hard, with 90 to 95 percent of all such life vanishing.
Investigation of another massive species wipeout, called the Cretaceous mass extinction, reveals yet another possible cause: an asteroid or comet colliding with the earth. Evidence dating to about 65 million years ago indicates that an extraterrestrial object slammed into the earth near the Yucatan Peninsula in what is today southeastern Mexico. There were multiple resulting events branching from the initial impact, ranging from tsunamis and earthquakes that blasted relatively local geography in the hours following touchdown to a curtain of dust and toxic vapors that literally stretched worldwide and blocked out the sun for months.
As was the case in other mass extinction causes, the impact could have also caused a substantial climate change. The general public recognizes the Cretaceous mass extinction because dinosaurs were wiped out, but a wide variety of plant and animal life took a hit too, with roughly 75 percent of all the planet’s species dying. When sunlight was blocked for an extended time, photosynthetic plants died off, including 90 percent of plankton in the oceans. With this vital first link in the food chain decimated, a domino effect tore through other species.
The causes of mass extinctions discussed here don’t quite cover all the possibilities being researched today. It can be argued that right now human activity is causing a mass extinction as habitats are destroyed and yet another global climate change is gearing up. There also could have been multiple extinction-causing extraterrestrial body impacts with the earth, or even near misses. Fortunately, even the most cataclysmic of events haven’t managed to wipe the earth’s slate completely clean. Surviving species found a way to diversify and fill in the abandoned niches.
What do you think? Is the possibility of mass extinction justification for continued space exploration?
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