Read the following excerpt from ted chiang's "exhalation":
i was a proponent of the competing school of thought, which held that our memories were stored in some medium in which the process of erasure was no more difficult than recording: perhaps in the rotation of gears, or the positions of a series of switches. this theory implied that everything we had forgotten was indeed lost, and our brains contained no histories older than those found in our libraries. one advantage of this theory was that it better explained why, when lungs are installed in those who have died from lack of air, the revived have no memories and are all but mindless: somehow the shock of death had reset all the gears or switches. the inscriptionists claimed the shock had merely misaligned the foil sheets, but no one was willing to kill a living person, even an imbecile, in order to resolve the debate. i had envisioned an experiment which might allow me to determine the truth conclusively, but it was a risky one, and deserved careful consideration before it was undertaken. i remained undecided for the longest time, until i heard more news about the clock anomaly. .

we are not really consuming air at all. the amount of air that i draw from each day's new pair of lungs is exactly as much as seeps out through the joints of my limbs and the seams of my casing, exactly as much as i am adding to the atmosphere around me; all i am doing is converting air at high pressure to air at low. with every movement of my body, i contribute to the equalization of pressure in our universe. with every thought that i have, i hasten the arrival of that fatal equilibrium.

identify two themes conveyed in this excerpt. how do these themes develop over the course of the story? be sure to refer to examples from the excerpt or story to support your analysis.