Approximately how long have homo sapiens been on earth, according to the fossil record?

Environmental differences within ecosystems are generally caused by

Approximately what wavelength of light is best absorbed by chlorophyll a

Which of the following is an advantage of using embryonic stem cells in medical research? a. the use of embryonic stem cells is much less expensive than the use of adult stem cells. o b. no living tissue is damaged when scientists use embryonic stem cells. o c. embryonic stem cells are able to differentiate into a wider range of cells than adult stem cells. d. there is no controversy surrounding the use of embryonic stem cells.