It is refreshing to read a book about our planet by an author who does not allow facts to be (i)__________ by politics: well aware of the political disputes about the effects of human activities on climate and biodiversity, this author does not permit them to (ii)__________ his comprehensive description of what we know about our biosphere. He emphasizes the enormous gaps in our knowledge, the sparseness of our observations, and the (iii)__________, calling attention to the many aspects of planetary evolution that must be better understood before we can accurately diagnose the condition of our planet..