Geophysical History of Socotra While it may never be described as a paradise by anyone who has actually visited it, Socotra is certainly home to a large number of exotic plants. Separated from the continent during the Tertiary period, the island hosts no indigenous mammals whatsoever, but its floral endemism rate is estimated at roughly 30 percent, making it one of the most bio diverse islands in the world. Included among some 815 vascular Explorations: An Undergraduate Research Journal 2005 Grainne Grant 122 plant species recorded on the island are at least seven species of Socotran Frankincense. Originally part of the coastal shelf of Africa, Socotra was separated from the larger landmass along with other continental fragments when the crust along the Gulf of Aden fractured some 15 million years ago. Following the violent tectonic events that divided Arabia from the Horn of Africa, the phenomenological evolution of the island has been comparatively quite slow, more or less limited to that caused by fluctuating ocean levels, as the tropical climate contributes little to erosive processes. The island lacks evidence of volcanic activity since the Paleozoic era, and geologists believe that there have been no substantial changes in either the form or composition of the Socotran landscape in the last 30,000 years. 9 Although stable for millennia, Socotra’s topography is nevertheless quite dramatic. Only 83 miles long and 26 miles across at its widest point, the surface of the island varies in altitude from the coastal marine terraces at 16-23 feet above sea- level to the Haggier Mountain range, the highest peak of which is 5,000 feet. The combination of this varied terrain with the unique local climate allows distinctive flora to flourish on Socotra. Situated at the convergence of the Northern Tropical and Sub-Equatorial climatic belts, Socotra is subject to annual monsoons from two directions. From late October to April, the winter monsoon blows northeast from the Arabian Sea, and from May to October the summer monsoon blows southwest from the Indian Ocean. Socotran “seasons” seem to be defined by the direction in which the winds are blowing. Average air temperatures vary less than 40° Fahrenheit between winter and summer, and evaporation capacity exceeds 78 inches year- round. Tropical cyclones raised by overlapping air currents lash the coast of the island in April and June, and occasionally in November and December as well. Although the island will never be described as wet, these storms ensure that annual precipitation is significantly higher on Socotra than on the continental landmasses that frame it, with rainfall over twelve inches annually in the Haggier range. 10 Layers of porous limestone overlie the plateaus at the base of the mountains, and the tiny pockets in this soft stone collect water beneath the soil rather than shedding it. The island’s many rift basins and valleys also contribute to water retention, with the result that there are natural springs near the mountains year-round. The mists surrounding the mountain peaks and a curtain of heavy fog at 492 feet above sea level also help to maintain consistent moisture levels. Runoff down the Haggier slopes keeps the mountainsides damp above 650 feet; between 650 and 1640 feet the arid light forests, which contain trees that produce frankincense, are found. In ancient times these small groves alone made Socotra worth settling in spite of the geographical and climatological hardships. In addition to spiritual and medical applications, frankincense had many social uses in the ancient world. Although the ancients lacked sophisticated distillation technology, 90% of some 200 chemical constituents of frankincense are soluble in alcohol, and frankincense was enjoyed as a relaxing additive to wine. 40 Additionally, the solvent extracts of frankincense are remarkably fixative, taking roughly six hours to evaporate. This made the resin particularly suited to perfumes and unguents, the former made with alcohol and the latter with animal fat or other viscous bases. Frankincense was even chewed as a breath-freshener, and used to make hair oil and “rejuvenating” facial creams. No external part of the human body was exempt from beauty treatments made with frankincense, just as no internal part was spared medically. Fourth-century Athens, a rather wealthy society, was home to professional perfumers and unguent boilers with their own specialized stalls in the agora, and apparently business was brisk.