Use the drop-down menus to answer each question about rock formation.
Which type of rock is formed from molten materials?
Which type of rock needs weathering or erosion to form?

How does the molecular clock work? a. it analyzes the brain functionality of two different species.b. it examines and compares the physical characteristics of two different species.c. it illustrates relationships between two different species.d. it compares the number of mutations that exist in the dna of two different species.

Which of the following statements about archaea and bacteria is true? a. neither is single-celled. b. they both have nuclear membranes. c. neither reproduces by binary fission. d. they both lack a nuclear membrane.

Why are scientists concerned about the depletion of the ozone levels in the stratosphere?