It is a sign from fossil land snail shells as located in ancient soils on the subtropical Eastern Canary Islands that the Spanish archipelago located off the North-Western African coast has become progressively drier over the last 50,000 years.

(Credit: Image courtesy of Southern Methodist University)

Certain isotopic measurements carried out on fossil land snail shells, have yielded oxygen isotope ratios indicating that the relative humidity on the islands was at a higher level 50,000 years ago, before undergoing a long-term decrease to the time of maximum global cooling and glaciations, some fifteen thousand to twenty thousand years ago. Such research was headed by Yurena Yates, a post-doctoral researcher, and geochemistry professor Crayton J. Yapp; based at the Roy M. Huffington Department of Earth Sciences of Southern Methodist University in Dallas, Texas.

The finding suggests that, relative humidity has truly oscillated somewhat in the midst of subsequent post-glacial climactic fluctuations; but it would end up decreasing even further to modern values. This is what has caused an overall dryness in the eastern Canary Islands over the last 50,000 years – according to Yanes. The low-altitude areas are marked by low annual rainfall rates and a landscape consisting of short grasses and shrubs. The research itself is an advancement of the understanding of the worldwide paleoclimate, at an important time in the history of human evolution: when hunting and gathering shifted to agriculture (originally in the Middle East, before spreading elsewhere).

This isotopic evidence is indicative of changing atmospheric and oceanic circulation in connection with the waxing, waning and disappearance of vast ice sheets during the last 50,000 year period, at mid-to-high latitudes along the continents of the Northern hemisphere. Furthermore, this research shows consistency with the observed decline in diversity of the very moisture-sensitive land snails.

About the land snail shells: they are abundant and sensitive to changes in the environment; and they are well-preserved as fossils. It is a fact that measuring the variations in fossil shells’ oxygen isotope ratios is capable of yielding information to do with changes in ancient-time climactic conditions. The shells are composed of calcium, oxygen and carbon, which together form the mineral aragonite.