What is the purpose of having a four-chambered heart?

Compare and contrast region e in the illustration above with region d. describe the physical characteristics of each region.

At which location in earth’s interior does the top density continue to increase as thickness decreases?

How can a geological time scale best be reconstructed? a) comparing vestigial structures in living species b) comparing homologous structures in living species c) examining homologous structures in fossil remains d) examining the written records of scientists from past cultures