The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) trap energy from the sun. Normal warming is mostly caused by natural gases.
The correct answer is - silver.
The Appalachian Mountain range, located in the eastern part of the United States, in close proximity to the Atlantic coastline, are rich in multiple natural resources. Some of the most common resources being the coal, petroleum and natural gas, iron, as well as lumber from multiple types of high quality trees. The silver, on the other hand, is not one of the natural resources that are abundant in this region of the country, thus can not be included into the riches of the Appalachians.
It is a product of the Old World.
