Trace the major processes in the evolution of the earth's ...

[iveyjurea]

Trace the major processes in the evolution of the earth's atmosphere from its beginning to the present.
 
  What will be an ideal response?

Question 2

The ________ were the first producers of substantial amounts of oxygen.
 
  Fill in the blank(s) with the appropriate word(s).

[at]

Answer to Question 1

Answer: The atmosphere has been greatly transformed since its early days rich in water vapor and carbon dioxide. The removal of the water vapor is easily explained: Upon cooling in the prehistoric atmosphere, it readily condensed and precipitated to the surface to form the oceans. Precipitation also contributed to the removal of carbon dioxide from the atmosphere. As raindrops fell through the CO2-rich atmosphere, some CO2 was dissolved in every drop. The transformation to an atmosphere high in oxygen depended on the advent of primitive, anaerobic bacteria (those that survive in the absence of oxygen) about 3.5 billion years ago. These primitive life-forms were the first in a long line of organisms that removed carbon dioxide from the air and replaced it with oxygen (these gases are exchanged freely between the oceans and the atmosphere). All of these processes gradually led to an increase in atmospheric oxygen at the expense of carbon dioxide. Although it constitutes a small portion of the material released by outgassing, nitrogen is removed from the atmosphere very slowly. As a result, its concentration has gradually increased to the point that it is now the main constituent of the atmosphere. Finally, argon, the third most abundant gas, is explained by slow seepage from the solid Earth of argon-40 with its 18 protons and 22 neutrons.

Answer to Question 2

Answer: anaerobic bacteria