Both petroleum and coal are made up of complex carbon-based molecules, and both originated with living creatures of some kind. both are vital sources of energy for the modern world and both were formed by geologic processes over millions of years. however, petroleum was mainly formed from the remains of ocean-dwelling microorganisms. coal, on the other hand, originated from decayed vegetation in ancient swamps and bogs. in any case, it took millions of years for both coal and oil to be produced. this is the case because it took that much time for overlying sediments to produce the unimaginable heat and pressure that would one day allow us to harvest these energy resources.
this passage uses a combination of comparison and contrast and

This passage uses a combination of comparison and contrast and development.

This part uses comparison between petroleum and coal (it highlights the common aspects):


"Both petroleum and coal are made up of complex carbon-based molecules, and both originated with living creatures of some kind. Both are vital sources of energy for the modern world and both were formed by geologic processes over millions of years"

This part uses contrast (it highlights the differences):

 
"However, petroleum was mainly formed from the remains of ocean-dwelling microorganisms. Coal, on the other hand, originated from decayed vegetation in ancient swamps and bogs."


This part also uses comparison:


"In any case, it took millions of years for both coal and oil to be produced"

And this last sentence is the use of development:

"This is the case because it took that much time for overlying sediments to produce the unimaginable heat and pressure that would one day allow us to harvest these energy resources"

Because the writer deepens into some aspects,explaining some characteristics of the fenomena or supporting the idea.

The comma attempts to set apart an essential element.

Argumentare apartenenta poeziei pelerinaj sentimental la genul liric