“The principal energy sources of our present industrial civilization are the so-called fossil fuels. We burn wood and oil, coal and natural gas, and, in the process, release waste gases, principally CO2, into the air. Consequently, the carbon dioxide content… — Carl Sagan Copy Share Image
“To understand how the first tree appeared on Earth, we must look back more than 3 billion years to Earth’s cooling off and changing from a molten sphere to one that had a solid crust. As it cooled, a thin… — Richard M. Ketchum Copy Share Image
