There are both natural and man-made sources of nutrients.
The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources.
Urban Talents, which was the majority of them, drew down from man-made sources by preference, and power stations were the most common target.
Most scientists believe that emissions from automobiles, power plants and other man-made sources are warming the Earth's atmosphere.
Radiation can come from both natural and man-made sources.
Radiation in our environment comes from both natural and man-made sources.
Annual emissions from man-made sources have increased by between three and four times since 1950.
The bulk of the pollution, they say, is from man-made sources.
Do not forget that all of us are daily exposed to ionizing radiation from natural and man-made sources.
But the pollution was not due to any sudden, large increase in the man-made sources that must be present for its formation.
