The rate at which hydrogen is supplied to the Earthby the solar wind, and the rate at which hydrogen escapes from the Earthby diffusion into space are compared 011 the basis of recent estimates. Itis found that the hydrogen supplied by the solar wind is roughly comparableto or may even be larger than present hydrogen losses. The Earthmay have lost most of its hydrogen at an early stage when, according toUrey and Miller (1959), Pox (1960) and others, the Earth had a reducing,instead of an

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... ng atmosphere. However, no sufficient evidence isyet available to determine whether the Earth is still losing more hydrogenthan it receives. The common notion that the Earth is still in the processof losing its hydrogen is therefore in question.