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=Where did the first cells come from?= To answer that question we must first understand what cells are made of. All cells on planet Earth are made up of four organic macromolecules; carbohydrates (sugar, starch), lipids (fats, oils, waxes), proteins (amino acid chains), and nucleic acids (DNA, RNA). Proteins are the building blocks of all cells and make up the majority of the mass in all living things.

We must also understand how organic compounds, the building blocks of life, arrived on Earth. Unfortunately, time travel is not yet possible and we cannot say with any certainty where, when or how they got here. Currently, there are two hypotheses worthy of consideration.

Hypothesis 1:
The extreme conditions on early Earth allowed for the spontaneous formation of various organic molecules including amino acids. Earth's early atmosphere included water but also hydrogen, methane and ammonia which spewed from volcanoes covering its' surface. Intense lightning storms and solar radiation triggered reactions between the gases in the atmosphere, forming organic molecules. Stanley Miller's and Harold Urey's experiment showed that the spontaneous generation of organic molecules can occur under similar conditions. http://upload.wikimedia.org/wikipedia/commons/5/59/MUexperiment.png

Hypothesis 2:
Recent discoveries in astrobiology suggest that organic molecules originated in space. NASA has confirmed that amino acids are present in the debris of comets. The early solar system was a violent place, in which Earth was under constant bombardment by comets and meteorites. It is plausible that the majority of Earth's water and the first organic compounds were brought here by comets.

[[image:comet_1294349c.jpg width="404" height="258"]]
http://i.telegraph.co.uk/telegraph/multimedia/archive/01294/comet_1294349c.jpg

In the space below, discuss which hypothesis seems most plausible to you.
i think the 2nd hypothesis is most plausible.i think this because you can not really determine what formed the first molecules of life. you can think of what happened but you can not really determine it. so that is why i think the second one is most plausible because it doesnt try and determine what made them.it just tells us what they think happened and it tells us facts of what happend back in the day with the commets always smashing into the earth, and with the building block of life forming the commets and meteorites and when they bombarded our planet it is very possible that that was how the first life forms came into play on our planet earth

-rebecca cavezza