A806.3 ng sample of an unknown radioactive substance was placed in storage and its mass measured periodically. after 47 days the amount of radioactive substance had decreased to 100.8 ng. how many half-lives of the unknown radioactive substance have occurred?

Skills of homo sapiens were found an excavation. the skulls were preserved because the bodies were frozen. so, these fossils are (blank) fossils.the image shows the evolution of skulls beginning 2 to 3 million years ago. based on the image, modern human skulls(blank) ape skulls.