Washington, October 28 (ANI): In a new research, fossil land snail shells found in ancient soils on the subtropical eastern Canary Islands have shown that the Spanish archipelago off the northwest coast of Africa were wetter 50,000 years ago, and since then, have become progressively drier.
The research was done by Yurena Yanes, a post-doctoral researcher, and Crayton J. Yapp, a geochemistry professor, both in the Roy M. Huffington Department of Earth Sciences at Southern Methodist University in Dallas, Texas.
According to the researchers, isotopic measurements performed on fossil land snail shells resulted in oxygen isotope ratios that suggest the relative humidity on the islands was higher 50,000 years ago, then experienced a long-term decrease to the time of maximum global cooling and glaciation about 15,000 to 20,000 years ago.
With subsequent post-glacial climatic fluctuations, relative humidity seems to have oscillated somewhat, but finally decreased even further to modern values.
Consequently the eastern Canary Islands experienced an overall increase in dryness during the last 50,000 years, eventually yielding the current semiarid conditions.
"Today the low-altitude eastern islands are characterized by low annual rainfall and a landscape of short grasses and shrubs," said Yanes.
The research advances understanding of the global paleoclimate during an important time in human evolution, when the transition from gathering and hunting to agriculture first occurred in the fertile Middle East and subsequently spread to Asia, North Africa and Europe.
"In the Canary Archipelago, land snails are one of the rare 'continuous' records of paleoclimatic conditions over the last 50,000 years," Yanes said.
"The results of this study are of great relevance to biologists and paleontologists investigating the evolution of plants and animals linked to climatic fluctuation in the islands," Yanes added.
The researchers' isotopic evidence reflects changing atmospheric and oceanic circulation associated with the waxing, waning and subsequent disappearance over the past 50,000 years of vast ice sheets at mid- to high latitudes on the continents of the Northern Hemisphere.
The research is also consistent with the observed decline in diversity of the highly moisture-sensitive land snails. (ANI)