Wednesday, September 26, 2007

Ah Yes, The Origin Of Life

Life as we know it is great, isn't it? I mean, we pay $1.75 for lunch everyday, we get hot chocolates in between periods 1 and 2, and we get do have.....well.....we get to engage in some controversial acts of impurity during AP Bio. But how did humans, and all animals for that matter come to be as they are today? We know evolution by Natural Selection has influenced the inhabitants of the world immensely, but where did these "common ancestors" that we talk about every day come from? How did cells come to be as they are today? And why does Sean fall asleep everyday in first period? All of these questions will be answered in this post.

What is Life?
Before we discuss how life came to be, we should first understand what life is.

Living things will always:
1) be comprised of cells
2) respond to stimuli (though not always to the same stimuli, nor in the same way)
3) maintain homeostasis
4) use energy to grow
5) change and mature
6) reproduce

So every living thing we know of obeys all of the "rules of life" as listed above, right?


As we learned today, viruses are made of protein, and use animals to reproduce. These six rules of life apply to most animals. And for those planning to use number 6 as an excuse to "hop on the good foot and do the bad thing", living things only have to have the ability to reproduce. Those who dont "get busy" are still deemed alive!

So, how did life come to be?

How Life Came To Be
There is no proven theory about how life began, but there are several hypotheses.

One hypothesis is one which is supported mainly by the Bible and believers in God.

Special Creation suggests that life began simply when God made it.

This hypothesis is NOT TESTABLE, and we can never be sure if this hypothesis is correct. This is obviously not the only hypothesis.

Extraterrestrial Origin suggests that organic materials came from comets and meteorites striking the Earth.

The important thing to remember about this theory is that it does not suggest that we descended from this guy....

It merely suggests that organic molecules arrived on Earth in comets and meteors that struck the Earth.

Spontaneous Abiotic Origin, which is the theory that suggests that the Big Bang occurred, states that life spontaneously evolved from inorganic molecules.

To see a video (only the first 40 seconds or so are really relevant) about the big bang, go here:
(sorry I couldn't embed it!)


The Condition Of Earth In It's Early Stages
When the Earth was first..."boomed" into existence, the atmosphere was completely unfit for humans and organisms like us.

Oceans were boiling...

.....Free oxygen was missing from the atmosphere....

....And lightning, UV radiation, and Volcanoes were the sources of energy.

So which Hypothesis Of The Origins Of Life is most likely???

Well, scientists Miller and Urey (with an "assist" by scientists Oparin and Haldane) modeled the conditions of early life as described above, and concluded that Spontaneous Abiotic Origin was possible. This is also the theory that is most widely accepted in the science community.

Origin Of Genetics
RNA stands for Ribonucleic Acid. RNA is like DNA, only without the sugars.
RNA is believed to be the first genetic material, as it encodes information, is able to replicate itself, supports evolution and inheritance, and has enzyme functions.
Some scientists opposed this idea by suggesting that the first genetic materials were proteins (enzymes). They argue that RNA, or anything for that matter, could not reproduce without enzymes.

BUT THE PROTEIN THEORY, as it has come to be known as, IS NOT BELIEVED TO BE CORRECT! So don't let that confuse you.

Key Events In The Origin Of Life
First off, the Earth....

...into existence 3.5-4 BILLION YEARS AGO!!!
Prokaryotes were great in number on Earth between 3.5 to 2 billion years ago.

The image on the left is what we should focus on here. It is an image of a 3.5 billion year old fossil of bacteria.
Free Oxygen was finally found on Earth 2.7 billion years ago. Photosynthetic bacteria probably produced this oxygen. This oxygen made aerobic respiration possible, which in turn made us and other animals possible.
The first Eukaryotes, who evolved from Prokaryotes, were then present on Earth. Essentially, Eukaryotes were organisms that had cells which contained a nucleus and other cell structures.
The first appearance of an organelle was that of Endoplasmic Reticulum.

Endoplasmic Reticulum is said to have formed when the plasma membrane of early cells folded into itself, and created the passageways which are now found in cells.
Similarly, cells did not originally have a source of energy. Cells were said to have engulfed a photosynthetic bacterium, which would, if not eaten, provide the cell with energy. In return, the cell provided protection and food for the bacterium. Eventually, the bacteria became mitochondria in cells. This is believed because the mitochondria resembles bacteria. The relationship between the cell and the bacterium is called endosymbiosis.
Endosymbiosis is the process of having an internal, mutual relationship with another organism.
Another important event in the developing world was the Cambrian explosion, which was a period of 10-20 million years in which most of the major phyla of animals appeared in the fossil record. This happened 543 million years ago, and heavily supports the theory of punctuated equilibrum, but that's a different story!!!
Other events include the Permian mass extinction, and the Cretaceous mass extinction, which was when all of the dinosaurs were wiped out.

Evolution of early mammals FINALLY began 125 million years ago, and became dominant and most abundant on the Earth.
The last thing we discussed in class today was how scientists classify life. Basically, there are currently 3 domain systems, into which all organisms are organized and sorted. In the domain Eukarya, there are 4 divisions: Fungi, Plantae, Animalia, and Protista.
This was a long class!!! But worth it! Living things are found all around us, and it is important to know where they came from, how they evolved, and how we organize and study them.
I'll leave you off with a quote:
"If God put me in your plans or not, I'm trippin', this drink got me sayin' alot, But I know that God put you in front of me." Kanye West (Stronger)
So what hypothesis of life does Kanye believe???
Thankyou for reading. I hope it was informative enough!

1 comment:

艾光 said...

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