Question

the gaia theory was first proposed by james lovelock a british research scientist. the theory holds that the planet earth is self - regulating, much like the human body.
to understand this idea, it helps to think of how the human immune system helps us to fight off illness and maintain a constant body temperature (roughly 98.6 degrees fahrenheit). the gaia theory suggests that the earth has a similar mechanism - like the immune system - which helps it maintain planetary stability and health.
lovelock formulated the gaia theory in the 1960s while he was working for nasa. at the time, he was trying to explain several conditions that puzzled him. among these conditions were:

• the sun provides more energy than it used to, and yet global surface temperatures have not increased in the same proportion.
• the chemical composition of the atmosphere around us, which is composed of 79% nitrogen, 20.7% oxygen, and 0.03% carbon dioxide, has changed very little over time.
• the levels of salt in the ocean have not changed.

to lovelock, the above facts demonstrated that our
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what is paragraph 2 mostly about?
a. a discussion of why the earth is unstable most of the time
b. a method for determining the temperature of the human body
c. an argument that the human immune system is ineffective
d. a way of understanding the earths regulatory mechanism

Explanation:

The second paragraph starts with "To understand this idea, it helps to think of how the human immune system helps us to fight off illness and maintain a constant body temperature (roughly 98.6 degrees Fahrenheit)". It then goes on to say "The Gaia theory suggests that the Earth has a similar mechanism—like the immune system—which helps it maintain planetary stability and health". So it's presenting a way (by comparing to the human body's regulatory mechanism - the immune system) to understand the Earth's regulatory mechanism.

Answer:

D. a way of understanding the Earth’s regulatory mechanism