Yes, the Earth is “work’d over and over with sour dead”, but the earth is the symbol of renewal, so why should they poison it? The earth and its environs are incorruptible. Like a body, the Earth can renew itself, but unlike a body, it can heal from any injury or poison. When “normal” plants first evolved, they took over the earth and corrupted its atmosphere with their toxic breaths. The Earth embraced this change and it and all its life adapted to these changes giving rise to our everyday world. Humans have become the plants poisoning the air, water, and soil without realizing that it is not the earth they are killing but themselves. The Earth can survive everything from nuclear war to asteroid impacts; however, those whom live on its surface are vulnerable to being brushed away like a proverbial insect.
The Earth purifies the poisons put into it, and it is capable of still putting forth the “grasses of spring,” but this is not an endless cycle. Eventually, the Earth will be corrupted by the poisons thrust into it, but the Earth will recover. If only after the sources have destroyed themselves.