Geologic time is divided into units based upon types of a. sedimentary rocks c. organisms b. climatic changes d. igneous rocks

The correct answer is C. Geologic time is divided into units based upon the types of organism present. There are four main eras when time is divided this way - the Hadean (which comes before the presence of life), the Archean (the era before eukaryotes), the Proterozoic (the time before more complicated, multicellular life forms), and the Phanerozoic which is the subsequent era since.