How far back do you define as 'primitive?'

There was a lot more Carbon Dioxide (from volcanic eruptions and bacteria)
The plants produced oxygen which supported animals.

Now go and write 8 pages on those two sentences.

Google.com

A few suggestions:

Primitive Atmosphere
Atmoshperical change (Although you'll probably just get global warming stuff)
DoMyHomeworkForMe.com

Early in Earth's life, it was composed of hydrogen cyanide, CO2, carbon monoxide, nitrogen, hydrogen sulfide, water (because since the Earth was so hot, all the water was evaporated) and ammonia. About 3 billion years ago, the earth was finally cool enough for water to fall, and basically the water just fell onto Earth. The ground back then was rich with iron and so it just floated on the early ocean's surface for a long time (the color of the ocean was brown). The sky was also a brilliant red since the compounds that make up the atmosphere today are very different from back then. While this was going on, water vapors that were dispersed onto the Earth contained amino acids and other organic compounds that were identified in Miller and Urey's Experiment. Later, these organic compounds produced proteinoid microspheres. These microsphere's largely resembled bacteria. Then, all of a sudden, photosynthetic bacteria appeared, there environment was rich in CO2, so they produced a large amount of oxygen into the air, which resulted in the iron crust on seas to sink to the bottom (which to this day is the world's main source of iron). A mass extinction took place, since most organisms could not adapt to this environment. The one's that could however, became oxygen dependent which resulted in us!

One of the biggest factors: Dinosaur flatulence was 98.6% pure oxygen.

Swedish Chemist Shop

"I want to buy a deodorant please"

"Ball or Aerosol?"

"Neither, I want it for my armpits!"

Courtesy of "Not the nine O'clock news"

Yeah. Teachers love when people take initiative like that. If you get any grief about it, I've got your back.

Posted By: Simmy

How does the earths primitive atmosphere differ from our present atmoshoere? What brought about this change in atmospheric composition and how is it thought to have led to the development of more complex life forms on earth?

First things first: In the primitive (the word you need is PRIMORDIAL) atmosphere, there was next to no oxygen, a much larger percentage of carbon dioxide, a monstrous amount of hydrogen and helium and it contained: sulpher dioxide, ferrous oxide, and relatively high amounts (2%+ of each) of methane and chlorine. This means - the atmosphere itself was highly caustic and toxic to what we would consider life. Were you dropped into that atmosphere, you would disappear within seconds. Further, this atmosphere would be incredibly hot (700-1000 degrees F+). In the later part of this period, volcanic activity was incessant.

Over time (approximately 2.5 billion years), the heat oxidized many of the chemicals into less caustic compounds, solutions of the various chemicals were made (these solutions being less caustic as well), and general density of components of the atmosphere increased, due to a heat-loss of much of the hydrogen and helium. The temperature of the atmosphere also declined significantly. Volcanic activity, while still relatively high, decreased significantly during this phase of earth's formation and the crust was nearly entirely formed. It is surmised that during this time frame, magnetic poles formed and in fact changed places (that is reversed polarity) about once per 75,000-100,000 years. Also during this time, the ozone layer was formed and lighter gases no longer escaped from our atmosphere due to high temperatures.

In the next 500,000 years, volcanism nearly stopped, the geothermal activity slowed incredibly, and worldwide temperatures reached a point similar (+/-20 degrees F) to what they are today. The content of the gaseous atmosphere reached levels very similar to what they are today, with perhaps a higher occurrence of carbon dioxide and a lower occurrence of oxygen. The magnetic poles stabilized to the position they are in today. Single cellular organisms began to form in this period of time (Approx. 850Million - 1 Billion years ago), the majority of which used photosynthesis to generate their own food. This process (over the next 250 Million years or so) created the balance of oxygen/carbon dioxide found in our current atmosphere.

In the past 100 years, however, a shift in the volume of carbon dioxide to oxygen has occurred unlike any seen in the past c 500 Million years. This can be directly attributed to one of two factors:
1- Normal biochemical shifts in the content of the atmosphere (although no evidence of such a drastic change can be found in geochemical science, again, in over 500 million years, when there was significant volcanism and the beginning formation of what is our current atmosphere).
2 - Human influence on the content of the atmosphere (all likely evidence points to this as the main factor).

Posted By: legatissimo

-- Under its current composition, it would be impossible for flight to evolve. The denser atmosphere of yesteryear made gliding significantly easier, which evolutionary biologists see as one of the crucial stepping stones towards flight.

So I can't grow my wings? But I wanted to be the first guy to fly solo over the Atlantic without the aid of a machine

trance i invented something for you, here's the prototype:

nice meeting you.

If we could find some workable pterodactyl DNA, a scientist friend of mine might consider trying to grow some and graft them. Getting your brain to use them, however, might be difficult. How attached are you to having arms?

Posted By: Trance

Posted By: Udoboy

How attached are you to having arms?

Is that some sort of a sick joke? You know for a fact my parents were each 1/2 spider each. I have 8 legs but no arms.

Good call on the pun. I had forgotten your arachnitudinousness, though. See my post in the apology thread.