German biologist, explorer, and founder of micropaleontology. At the request of his father, who intended him for the church, Christian Gottfried Ehrenberg studied theology at Leipzig, near the town of Delitzsch where he was raised, before switching to medicine and natural sciences. At the University of Berlin, where he completed his medical degree, he was introduced to microscopy by Karl Rudolphi and Heinrich Link. For his doctorate, he described 250 species of fungi from the Berlin district (including 62 new species) to prove, against the current wisdom, that fungi develop from spores and show constancy of species. His subsequent research, published in 1819 and 1821, continued to refute the theory of spontaneous generation, by demonstrating that sexual reproduction occurs in molds and fungi. As a student in Berlin, he also met and befriended fellow naturalist Wilhelm Hemprich, who shared his interest in scientific exploration. The two friends made plans for an expedition to Madagascar, which they had to cancel when Ehrenberg accepted a temporary position at Königsberg. As an alternative, they convinced the Berlin Academy to sponsor them as naturalists on an archaeological expedition to Egypt, which was being led by the Prussian General von Minutoli.

The expedition was a total failure. After its disorderly first journey across the Lybian desert, it collapsed in Alexandria. There an outbreak of typhus killed several members of the expedition, prompting Ehrenberg and Hemprich to set out on their own, towards the Nubian province of Dongola. Ehrenberg was already sick with fever when they left the city in March 1821 to travel upriver, but in the dry air of the desert Hemprich was able to nurse him back to health. They explored the natural history of the upper Nile until their funds were exhausted two years later. Returning in 1823 to Alexandria with their collections and hoping to raise money to continue their travels, they eventually persuaded the Austrian consul to fund a second journey. This time they travelled eastward to the Sinai Peninsula. After sailing down the Gulf of Suez, they made their base at El Tur, on the southwest coast of the Sinai Peninsula, where they remained for nine months. While Hemprich took the material they had collected to Alexandria, Ehrenberg stayed behind to study the corals and medusae of the Red Sea. They then pressed onward through Syria to Lebanon, returning to Egypt in August 1824 with some of their richest plant collections. In November they headed for Massawa (now in Eritrea), intending to explore the interior of Abyssinia. On their southward journey they called at several ports along the coast of the Red Sea, visited the Dahlak archipelago and the Farasan Islands, and made an excursion from Djedda to Mecca. But the long journey took its toll on Hemprich's health. He was suffering from exhaustion by the time they landed at the port of Massawa, and died there of fever; Ehrenberg headed back to Europe, without seeing Abyssinia, the last survivor of von Minutoli's expedition.

During their five years in Africa and Arabia, Ehrenberg and Hemprich accumulated an enormous natural history collection: 114 crates were needed to pack up their zoological, botanical and mineralogical specimens, their archaeological and ethnographic artefacts (including six manuscripts of ancient Arab physicians), and their many maps and sketches. Only a fraction of the collection reached Berlin in a usable state. Some of the crates were damaged in quarantine, their contents destroyed or so disarranged as to prove indescribable when viewed later; labels and sketches were lost; living plants were killed by frost on the voyage; and some of the collection went missing in unauthorized sales. Among the specimens that survived were 1035 plants from Egypt and 700 plants from Saudi Arabia and Ethiopia. Ehrenberg eventually published two volumes of their discoveries, Symbolae Physic (1828-1834), under both their names, and an account of their travels, but never fulfilled his plan for a comprehensive work on the collection. Instead the majority of the discoveries from the collection were made by others, especially his colleagues in the Berlin Academy of Sciences; Alexander von Humboldt, Heinrich Lichtenstein, Heinrich Link, Karl Rudophi, and Christian Weiss, all reported on individual findings of the expedition, which included many new species.

Neither did Ehrenberg publish any notes on his plant collections from his eight-month journey across eastern Russia (1829) with the mineralogist Gustav Rose under the leadership of Alexander von Humboldt. Instead, after this expedition, he dedicated himself to the study of microscopic organisms. Over the next 30 years he discovered hundreds of new genera and thousands of new species in samples of water, soil, sediment, and rock. He was the first to describe coccoliths in limestone and chalk and the first to explain that phosphorence in the sea was caused by bioluminescent marine organisms. He produced nearly 400 publications, mostly concerned with diatoms, although he also studied other protists, particularly radiolarians. His monumental works, Die Infusorienthierchen als volkommene Organisme and Mikrogeologie, were foundational texts for a new branch of science, micropaleontology.

Ehrenberg was appointed professor of medicine at Berlin University in 1827, serving four periods as Dean and elected Vice-Chancellor in 1855. He was a foreign member of the Royal Society of London from 1837 and elected to the French Academy of Sciences in 1841. The Royal Geological Society awarded him their Wollaston Medal in 1839. He received the first ever Leeuwenhoek Medal in 1877.

Sources:
C.C. Gillespie (ed.), Dictionary of Scientific Biography, IV: 288-292
W.A.S. Sarjeant, 1978, "Hundredth year memorium: Christian Gottfried Ehrenberg 1795-1877", Palynology, 2: 209-211.