Complex sentence: The lack of air and moisture allowed for the objects to remain underground with little to no deterioration, which meant that, once excavated, the site had a wealth of sources and evidence for analysis, giving detail into the lives of the Pompeiians.
Split into simpler sentences: The lack of air and moisture let objects remain underground with little to no deterioration. Once excavated, the site provided a wealth of source material and evidence for analysis, giving detail into the lives of the Pompeiians.