unpolluted

"We argue that at low metallicity -- galaxy environments that are relatively unpolluted -- there is a 10-million-year delay in the start of strong superwinds, which, in turn, results in higher star formation."

But in between the galaxies at that time were large amounts of fresh, unpolluted gas, streaming down to the galaxies faster than the stars can keep up.

Without them, we cannot ensure stable global food systems and economies, let alone provide clean air and unpolluted water for the eight billion people who inhabit this planet.

The dump is a repository of both polluted and unpolluted sediment that has been dredged from a series of rivers and canals that connect Lake Michigan to the Mississippi River.

Even the wide expanse of stars normally visible in the unpolluted winter sky was hidden behind rain clouds on that gloomy day.