Brown University researchers have discovered that North Africa remained relatively wet even during a period of global climate change – a finding that challenges the link between drying and the paving of humanity.
Surprising new evidence suggests that North Africa was wetter than previously thought, at a critical time in human evolution.
The study challenges the widely held belief that North Africa became arid about 3 million years ago – a period when the first hominins appear in the fossil record.
The study, led by researchers at Brown University, found that rainfall patterns in North Africa remained nearly stable between 3.5 and 2.5 million years ago, a period when Earth experienced dramatic climate changes, including cooling in the Northern Hemisphere and permanent ice cover in Greenland.
The research findings, published in the journal Science Advances, challenge the notion that the climate in North Africa became drier during this period. This notion linked the desiccation to the emergence of the first Homo species, and led to speculation that the continental climate contributed to the acceleration of human evolution.
A closer look at ancient rainfall
The new study used a more direct indicator of precipitation – an analysis of leaf waxes produced by land plants.
"Plants produce these waxes during the summer growing season, so they provide a clear signal of rainfall during that time," said Bryce Mitsuvanaga, who led the study as a doctoral student in the Department of Earth and Environmental Sciences at Brown University and is now a postdoctoral fellow at Harvard. "We found that precipitation patterns remained virtually unchanged, even as global temperature changes and glaciers increased."
Early evidence for aridity in North Africa was based on dust in marine sediments off the coast of West Africa. Initial explanations suggested that increased terrestrial dust reflected desertification as a result of a weakening of the summer monsoon.
The new study analyzed leaf waxes from those sediment cores—these waxes retain the hydrogen signature of water absorbed by plants. Water containing light hydrogen indicates prolonged or more frequent rainfall.
Stability in rainfall patterns
The analysis revealed that there was no significant aridity during the transition from the Pliocene to the Pleistocene. Summer precipitation patterns remained stable on both sides of the chronological boundary, indicating that the African climate was not significantly affected by the global changes of the period – the decrease in temperature and the increase in glacier cover.
The researchers believe that the large amount of dust identified in previous studies was due to changes in winds and not a decrease in precipitation.
Implications for the past and future
Because carbon dioxide levels about 2.5 million years ago were similar to those of today (but then they decreased and today they are increasing), we can learn from the past to predict a possible future in a region that already suffers from water shortages.
Professor Jim Russell, a senior researcher on the study, said the results raise new questions about Africa's climatic history and its impact on human evolution. It was previously thought that environmental desiccation encouraged upright walking and savannah life, but now the story is becoming more complex.
"The findings call for new research into when and why the African environment changed and became a continent, and for the development of new theories about human origins," Russell concluded.
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It seems that even then the residents fled to Europe…
The theory presented in the book "Scars of Evolution" is the most convincing and logical theory, and as here - the evidence supports it.
Apes evolved in a wet environment. Standing upright in a dry environment is not advantageous, and breath control is necessary in water but not on land.