How Did Life Begin?
01/12/2010 § 1 Comment
In class, we’ve started a new unit right after our Molecular Genetics unit. This time, the unit is Evolution and how life began and evolved into the complex organisms they are today. The first chapter of this unit was “How did life begin?” which talks about the earth’s age based on scientists’ measurements of rock ages and how long they’ve been on earth. The chapter also talked about the beginning of molecules and the more complex organic molecules that became “the building blocks of the first cells”.
As of now, I’m a little unclear as to what the unit’s essay question will be but looking at the online course schedule’s collection of possible essay questions, (How did eukaryotic cells originate?, What are the main points of the theory of evolution?, and How are new species formed?) I can guess that our essay question this unit has to go along the lines of evolution’s importance or literally how life began.
In class and in the textbook, we learned of radiometric dating, which is the estimation of the age of an object by measuring its content of radioactive isotopes, also known as radioisotopes. When these unstable isotopes break down and ‘decay’, other smaller and stabler isotopes are formed. From this, a half-life is the time it takes for half of a given amount of a radioisotope to decay. Through half-lives, scientists can calculate how many millions or billions of years have passed since the rock formed, therefore they can find the age of the Earth as well.
We were also introduced to two main theories as to how the basic chemicals of life formed on Earth. The first—and unstable—theory came from the Russian scientistA. I. Oparin and the English scientist J. B. S. Haldane. They proposed that the early earth’s waters were filled with many different organic molecules; similarly to how soup has so many vegetables in it. They called it the Primordial Soup. This theory wasn’t the most accurate—and they knew it—because back when the Earth was very young, there was no ozone layer to rays like ultraviolet rays from the sun which can damage the molecules Oparin and Haldane said were in their Primordial Soup. Back then, without the ozone layer, the more complex molecules (ex. ammonia/methane) wouldn’t be on earth due to the ultraviolet rays from the sun and such sources of energy. However, the whole ordeal is still unknown.
Another scientist, Louis Lerman suggested that the formation of chemicals took place in bubbles underwater. Firstly, the gases (like ammonia and methane) were trapped in underwater bubbles that came from underwater volcanoes. Inside the protective bubbles, chemical reactions happened faster and were protected. When the bubbles rose to the surface and popped, the gases were released into the air, to be carried by winds and exposed to more chemical reactions like lightning. By the time they fall back to sea, they’ve become more complex and the whole cycle starts again but with more complex gases which probably started the formation of more complex molecules.
In class, we also learned that since RNA molecules can act like enzymes, because they can act as catalysts and since some RNA (like messenger RNA) can store information, scientists concluded that RNA was among the first of molecules to be the first self-replicating information-storing molecules. RNA can also join together to become a polymer (a repeating chain of subunits—like nucleotides, in this case). The polymer RNA eventually mutated to make protein that would help it evolve and make DNA from RNA.
We started talking about the importance of membranes for a cell in class as well, but as far as my understanding of the textbook information, this is what I know.