Scientist: All other things being equal, the intensity of heat increases as the distance from the heat source decreases. Knowing this, most people conclude that the Earth`s seasons are caused by the Earth`s changing distance from the sun. In other words, winter occurs when the Earth is far from the sun, and summer occurs when the earth is close to the sun. However, we know that as North America experiences summer, South America experiences winter, even though the difference in the continents' distance to the sun is negligible. Therefore, the earth`s changing distance from the sun does not cause the seasons.
In the argument, the two portions in boldface play which of the following roles?
【选项】The first describes a common belief that the scientist later deems to be ill conceived; the second is evidence against this belief.