| Abstrakt: |
RECENTLY published age determinations1,2together with other figures3from British Guiana can be used to give more information about the Pre-Cambrian atmosphere. Rutten4has suggested that a tentative age of 1,000 million years for the oldest geological ‘red beds’ indicates a provisional minimum age for the present oxygenic atmosphere. He further suggests that the transition between the latter and an earlier anoxygenic atmosphere occurred between 2,000 and 1,000 m.y. ago. Older ‘red beds’ occur in British Guiana and it is postulated here that the above transition was probably between 3,000 and 2,500 m.y. ago. |
