Thursday, October 16, 2014

Hypotheses of Life's Origin

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Hypothesis of Life’s Origin
Kelly Nienburg, AP Biology P.4
October 16, 2014


Today we'll be talking about several popular hypotheses of how life on earth came
to be. I hope y'all learn something. :)

The earth was first predicted, in 1897, to be between 20 and 40 million years old. But even 40 million years was not enough time for the level of evolution that the earth has.

It was determined in 1956 by radiometric dating on meteorites that the earth is approximately 4.5 billion years old. The earth was also unsuitable for life for the first half a billion years it was formed because it was essentially a molten ball of lava and toxic gasses.

It took half a million years for the earth to cool down enough and produce water. But how did life come along? Well, there are many hypotheses about how life on Earth came to be. 

One of the most famous is the “Organic Soup Model,” which shows how with water with only nutrients and gases that were thought to cover early Earth, organic compounds were formed. These compounds are the basics of genetic material that all life contains.














Another popular hypothesis is that a meteor brought organic compounds and amino acids to earth.  What makes this possible is that in Australia, an asteroid rich in organic compounds and containing 70 amino acids and nucleotide bases was discovered.


These organic molecules combines with Earth’s inorganic precursors could have, in both cases, synthesized with all the free energy available and became monomers. The absence of a large amount of oxygen helped also.

These monomers then joined and formed into more complex molecules called polymers, including nucleotides and amino acids. These new polymers had the ability to reproduce, store and transfer information, like ones in current organisms’ cells.


Soon enough, these polymers were packaged into probionts, which were what could be called the first cell-like things, as they had fatty membranes. These probionts then formed into liposomes, which contained the first lipid bilayers when added to water. This membrane was semi-permeable.

The RNA World Hypothesis proposes that RNA may have been the planet’s earliest genetic material, as it essentially runs protein synthesis and even has enzyme-like functions. RNA later on provides the foundation for DNA.



The oldest fossils knows were made of many layers of bacteria and sediment. They are called Stomatolites. These bacteria were autotrophic and some photosynthetic. These prokaryotes were the only known life form on earth for about 1.5 bya. These photosynthetic bacteria created a ton of oxygen, which caused many species of prokaryotes to become extinct. One of these kinds of bacteria are the LCA, or last known common ancestor to all life.



The first eukaryotic cells came into existence around 2.1-2.7 bya. They were a sort of chimera of an aerobic heterotroph and a host cell. The ancestors to what we know today as Mitochondria and Chloroplasts entered the cell. Plastids came about to be inside the cell later on. These allowed the new cells to metabolize energy.

Next came multicellular prokaryotes, around 1.5 bya after the first eukaryotes were formed. After these first formed, these cells began to evolve into eukaryotic animals, known as the Cambrian period. Autotrophic bacteria evolved, forming a waterproof wax coating to prevent desiccation, roots, spores to protect them from radiation, a vascular system to transfer water and nutrients through the plant from the roots and tough cells for support(stems); all of these allowed for the colonization of land by plants. Animals soon evolved their own mutations and were able to populate the land soon after the plants.

And that's how life most likely came to be! :)








Citations:
http://resources0.news.com.au/images/2011/08/10/1226112/560528-meteorite-dna.jpg
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh66GOEK2oAi-H3IU-WRWlxvAvBNPs7jC67DS7CJlGpby5TZ2PFYlmtlZLOknJqqCLznmVapkGj6mhADTa4b4WOe7fw6-9i2Wn8-Nt9L6qQnTHXU_FtBMqN15pJVCpx77oRe0esnrTxm-M/s1600-h/Miller-Urey_experiment_svg.png
http://media-2.web.britannica.com/eb-media/01/123001-004-2FC93D97.jpg
http://www.rsc.org/images/wochner1HR_410_tcm18-200601.jpg
http://whyevolutionistrue.files.wordpress.com/2011/08/fossil-stromatolite.jpeg
http://upload.wikimedia.org/wikipedia/commons/e/e8/Frangula_alnus_with_magnesium_deficiency.jpg
http://www.mlhi.org/science/period2/Period2_files/image007.gif







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