theory of continental drift, the world was made up of a single continent through most of geologic time. ... According to the generally acceptedplate-tectonics theory<span>, scientists believe that Earth's surface is broken into a number of shifting slabs or </span>plates<span>, which average about 50 miles in thickness....</span>
During the second trimester, energy needs of pregnant women are 340 more kcalories per day than those of nonpregnant women.
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