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Environmentalism.

Levels of air pollution rose during the Industrial Revolution, sparking the first modern environmental laws to be passed in the mid-19th century.

Environmentalism.

John Muir also known as "John of the Mountains" and "Father of the National Parks", was a Scottish-born American naturalist, author, environmental philosopher, botanist, zoologist, glaciologist, and early advocate for the preservation of wilderness in the United States.

Environmentalism.

Photos of the Earth from outer space provided both new insights and new reasons for concern over Earth's seemingly small and unique place in the universe (composite images of Earth generated by NASA in 2001 (left) and 2002 (right)).