Why so earth scientists use 2 different ways of classifying earths layers ?

Ecologist: the scottish highlands were once the site of extensive forests, but these forests have mostly disappeared and been replaced by peat bogs. the common view is that the highlands’ deforestation was caused by human activity, especially agriculture. however, [agriculture began in the highlands less than 2,000 years ago]. peat bogs, which consist of compressed decayed vegetable matter, build up by only about one footper 1,000 years and, [throughout the highlands, remains of trees in peat bogs are almost all at depths great than four feet]. since climate changes that occurred between 7,000 and 4,000 years ago favored the development of peat bogs rather than the survival of forests, the deforestation was more likely the result of natural processes than of human activity.in the ecologist’s argument the two portions in [parenthesis] play which of the following roles? a. the first is evidence that has been used in support of a position that the ecologist rejects; the second is a finding that the ecologist uses to counter that evidence.b. the first is evidence that, in light of the evidence provided in the second, serves as grounds for the ecologist’s rejection of a certain position.c. the first is a position that the ecologist rejects; the second is evidence that has been used in support of that position.d. the first is a position that the ecologist rejects; the second provides evidence in support of that rejection.e. the first is a position for which the ecologist argues; the second provides evidence to support that position.