Which sphere allows the human breathe oxygen from the air to the lungs that involves matter starting and ending ?

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.

"does stress during a woman's first trimester of a pregnancy affect the infant's birth weight? " is a

Ts assignment - snow day assignment genetic variation and natural selection natural selection relies on genetic variation. in any population of beetles, there are alleles for brown or green color. what happens to the genotype and the phenotype of the beetle population when there are distinct advantages and disadvantages due to color? order the steps that take place during natural selection in this beetle population.