A daily input of water, food, and energy of various kinds is matched by an output of sewage, solid waste, air pollutants, energy, and materials that have been transformed in some way.
Because of her efforts, dozens of toxic sites across the country have been cleaned up, and one chemical industry spokesperson calls her "a top gun for the environmental movement".
But, unlike the cores of the inner planets, the Moon's core contains little or no iron, while the typical planet-forming materials were quite rich in iron.
Such ice cores trap gases, bits of dust, and other chemicals that were present in the snow that fell over Greenland for thousands of years and then became compressed into ice.