Which of the following sentence is a result of natural erosion? a. desert sands b. lost seed germination c. widened valleys d. all of the above

Which of the following is not a place where hydrogen can be found on earth? a. natural gas well b. atmosphere c. water d. mine

Some gamma ray bursts are hypothesized to come from mergers of neutron stars or black holes. if this hypothesis is correct, what else should we in principle be able to detect from such mergers? a. gravitiational waves b. x-ray bursts c. significant disruption of gas thousands of light-years away in the surrounding galaxy d. an "afterglow" of bright visible light, lasting for weeks

Which of the following can scientists estimate geologic time? a.observing rock sequences b.radiometric dating c.comparing fossils d.all of these