Astudent writes in a laboratory notebook: i placed a piece of iron in a beaker of water and the iron sank to the bottom of the beaker. -- what the student wrote in the laboratory notebook is an example of a(n) *
1. observation
2. prediction
3. inference
hypothesis

Which of the following must be true for a fossil organism to be useful as an index fossil? a. the fossil organism must be widespread geographically. b. the fossil organism must be abundant. c. the fossil organism must be limited to a short span of geologic time. d. all of the above.