We define The Primordial Thesis of Cancer, relating the nature and origin of cancer to the early history of the earth and the first appearance of life and noting that the initial absence of oxygen in the earth's atmosphere resulted in anaerobic microorganisms whose gene structure partly persists in present-day mammalian cells. Under various conditions a mammalian cell will transform from a respiratory state, requiring oxygen, to a glycolytic or cancerous state (primordial) not requiring oxygen, for the purpose of survival. Implicit in this thesis are useful therapeutic modalities, universal cancer screening potentials and new approaches to understanding the multiple 'causes' of cancer.