It is said that 99 percent of all species that ever lived have gone extinct. Earth, it seems, is a tough place to call home. Our planet has gone through Ice Ages and global warming trends, it has been hit by comets and asteroids (leading, in one case, to a mass extinction that felled the mighty dinosaurs), and the amount of oxygen in the atmosphere has risen and fallen over time. Our planet is always in a state of flux, and life must adapt to these changes or die.
It is a known geological fact that CO2 released into the atmosphere is primarily caused by tectonic activity. According to Sasselov, Earth's mass helps keeps tectonics in action. The more massive a planet, the hotter its interior. Tectonic plates slide on a layer of molten rock beneath the crust called the mantle. Convective currents within the mantle push the plates around. For smaller planets like Mars, the interior is not hot enough to drive tectonics.
Continents bang together, forming mountains, only to be later torn apart. Islands grow from underwater volcanoes, and elements are liberated from rocks when they are melted beneath the crust.
While all this geologic activity makes us literally stand on shaky ground, scientists have come to believe that tectonics is one of the key features of our planet which makes life possible. If not for tectonics, carbon needed by life would stay locked within rocks.
The fear today is that too much carbon dioxide in the atmosphere will lead to global warming. Yet too little carbon dioxide in the atmosphere would make Earth a much colder place, and the photosynthetic plants and algae that rely on CO2 would perish. The demise of these oxygen-producing organisms would leave us all gasping for breath.
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