What do climatologist study about fossil seashells in rock sediments to learn about climate? the shapes of the shells
the ratio of magnesium to calcium in the shells
the strontium content
the chemical traces of alkenones

Which were the most important issues during the presidential election of 2008? a.economic downturn and environmental protection b.two overseas wars and economic downturn c.two overseas wars and campaign spending d.environmental protection and campaign spending