Jennie Talbot shares her musings following the class discussion last week in Biogeography (Biol 275).
In class we discussed the idea that niches are places that supply a particular organism with all of the resources required for it to thrive. The discussion led to questions regarding how much the niche impacted the species and, in turn, how much the species impacted the niche. For example, a plant species may thrive on the side of a mountain because it is here that the plant can find soil with good nutrients, adequate sun light, and reasonable temperatures. However, as more and more plants colonize the side of the mountain, transpiration will occur at a higher rate, which will produce more moisture in the air and, ultimately cause more rain to fall. The plant’s root system will hold the nutrient-rich soil despite all of the rain. Animals may come and feed on the well-nourished plants and, in turn defecate onto the soil, adding more nutrients for the plants to use. As more and more plants grow in this favorable environment, it is likely that the side of the mountain will get more rain then it did before the plants migrated to this location. Likewise, the side of the mountain may have better soil because of the wildlife that eat the plants. In fact, the wildlife may migrate to this newly colonized region on the mountainside because of the resources available. Therefore, the cycle will continue with more rain, better soil nutrients, healthier plants, and new wildlife. In this way, the side of the mountain, which may at one point have been completely void of life, has become a bustling habitat for multiple species.
So then I have to ask the question, “Was earth created for life or did life mold the earth into what it is today?” Of course, people may say, “Yes, the earth was created for life.” Well, Harold C. Urey submits that the earliest atmosphere of earth was composed mostly of hydrogen, methane, and nitrogen with only trace amounts of other elements such as carbon and oxygen. Over time a bunch of chemical reactions occurred (if you want to know all of the reactions, read Urey’s paper) and the earth’s atmosphere changed from being predominantly hydrogen and methane based to being highly oxidized with a lot of free energy created from oxidation reactions. The available free energy made it possible for a few primitive organisms to thrive. From here on out, those small organisms began to colonize earth. Current literature suggests that heterotrophic cells evolved 3.5 billion years ago followed by autotrophic cells (somewhere around 2.7 billion years ago), eukaryotes (2 billion years ago) and then multicellular organisms (Kardong, 2005). Because of the newly formed organisms on the planet, compounds that the earth had not seen yet (like isotopes of sulfur) were made and the compounds that were available already could be molded into something that could be used by another organism (Urey, 1952; Kasting, 1993).
So what does all of that mean? It seems to me that when the earth was created, it was completely uninhabitable. Which may mean the earth was not created for life and it is because of life, that the earth is habitable now. When the earth first came to be, there were atmospheric elements that began to interact with one another. From this energy was released, organic molecules were formed and the genesis of life began. At this point in the story, organisms have done nothing to alter the earth. However, with the birth of the first autotrophic cells (and the use of photosynthesis), living organisms began to transform the earth into something that could sustain life. Since then life has molded the planet into what it is today. Of course, it is likely that life has not molded the entire planet (as in, I am not sure that living organisms have any impact on the core of the planet itself…but this is science, so you never know, something could be discovered ☺) and who knows about our impact on the entire solar system. Nevertheless, in terms of niches within our range of exploration on the surface of the earth, it seems that living organisms can have a drastic, sometimes detrimental, impact on their habitats. Image what the world would look like if there was no deforestation or animal poaching. Imagine if the mosquitoes that bite us incessantly were not provided with stagnant water supplies in the rims of old tires and so could not reproduce in new habitats and spread deadly diseases to the inhabitants of those places. What if plumes of dinoflagellates did not blanket the ocean and poison thousands of fish each year. What if asparagus seeds did not float on water? What if fungus did not decompose leaf litter on the forest floor? What would the world look like without millions of species changing the world into a place called home?
Okay, so the end of that paragraph was a little cheesy. But truly, without life shaping the planet what would the planet look like? From these thoughts, I believe, at least for now, that living organisms have morphed the earth into what we know today. Without life on this planet, the earth would look completely different.
Sources
Kardong, Kenneth V. 2007. An Introduction to Biological Evolution. 2nd ed. Boston: McGraw-Hill Companies, Inc., 49-54.
J. Kasting (1993). Earth's early atmosphere Science, 259 (5097), 920-926 DOI: 10.1126/science.11536547
Harold C. Urey (1952). On the Early Chemical History of the Earth and the Origin of Life Proceedings of the National Academy of Sciences, 38 (4), 351-363
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