Which gas forms 21% of earth's atmosphere?
a.-argon
b.-carbon dioxide
c.-nitrogen
d.-oxygen

Plants can have a positive and negative effect on the rate of weathering

In the following diagram, four different index fossils are labeled: which of the labeled fossils comes from the oldest organism? a b c d

Which statements describe characteristics of mdcs? higher standard of living increased agricultural focus more access to health care more access to transportation and communication more industry reduced educational opportunities shorter life expectancy