The introduction to this chapter, which describes the sequencing of 4000-year-old DNA, emphasizes DNA’s extreme stability. What aspects of DNA’s structure contribute to the stability of the molecule? Why is RNA less stable than DNA?

DNA is more stable than RNA due to the absence of a hydroxyl group in the 2' position of the deoxyribose sugar.

Explanation:

Each RNA or ribonucleic acid molecule is composed of a pentose sugar called Ribose, a  phosphate group and a nitrogenous base.A RNA chain is made up of a ribose phosphate backbone linked by phosphodiester bonds.The Ribose sugar has a hydroxyl group in the 2' position.This hydroxyl group is susceptible to hydrolysis in presence of alkaline condition.This hydrolysis causes the breakdown of the phosphodiester linkage between the phosphate group and the ribose sugar, causing the disruption of the entire RNA structure.Each DNA or deoxyribonucleic acid is composed of a pentose sugar called Deoxyribose, a phosphate group and a nitrogenous base.A DNA chain is made up of a deoxyribose  phosphate backbone linked by phosphodiester bonds.In the Deoxyribose sugar, the 2' hydroxyl group is absent and hence it is no longer susceptible to hydrolysis under alkaline conditions.Hence, DNA is more stable than RNA.