The African humid period was not the first such phase; evidence for about 230 older such green Sahara/wet periods exist going back perhaps to the first appearance of the Sahara 7-8 million years ago, for example during Marine Isotope Stage 5 a and c. Earlier humid periods appear to have been more intense than the AHP of the Holocene, including the exceptionally intense Eemian humid period which provided the pathways for early humans to cross Arabia and Northern Africa and which, together with later moist periods, has been linked to expansions of the Aterian populations. Such humid periods are usually associated with interglacials, while glacial stages correlate to dry periods.