Alfred Harker (1859-1939) was born on 19 February 1859 at Kingston-upon-Hull. Harkers father was the Yorkshire corn merchant Portas Hewart Harker, his mother was Ellen Mary Harker. He attended Hull and East Riding College, and the private Clewar House School (Windsor).

He enrolled as an undergraduate at St. John's College (Cambridge) from where he graduated with an M.A. in 18 January 1882, after which he lectured in Physics at Newnham College. In 1884 he held the post of Demonstrator in the Geology Department under Thomas McKenny Hughes (whom he regarded his mentor), as College lecturer in Physics at St Johns in 1892, University Lecturer in 1904, and as Reader in Petrology in 1918.

His duties included teaching Mineralogy and Petrology to students. Harker was elected as a College Fellow of St. Johns in 1885. A geological tour of Western Europe in 1887 introduced him to the metamorphic rocks of the Ardennes which proved to be an influential experience to his continuing research.

Harker accompanied Professor Thomas McKenny-Hughes to the United States in 1891 where they attended the 5th International Geological Congress. This was the first time the event had been held outside of Europe. Harkers two geological notebooks/travel diaries from this time are held in the Sedgwick archive and contain many sketched observations of the people and places he encountered on the excursion.

In 1895, Harker commenced employment with the Geological Survey of Great Britain on a part-time basis. Professor McKenny-Hughes had also worked with the Survey, but Harkers invitation came from the then Director General, Archibald Geikie. This was to assist in the mapping and determination of the igneous rocks of the Isle of Skye and the small Isles. This association lasted some 10 years or so. At this time, he also became a Member of the Scottish Mountaineering Club, photographs of which are in the collection.

Harkers active fieldwork programme also saw him collaborating with Professor J. E. Marr of the Department of Geology on the volcanic rocks of the Lake District in 1889. The Sedgwick Memorial Museum opened in 1904 and three years later, Harker published research on material he had prepared petrological rock slices of. He named the petrological samples brought back by Charles Darwin as the Beagle Collection of Rocks. He and other British geologists pioneered the use of thin sections and the petrographic microscope in interpretive petrology.

Harker became a member of the Geological Society of London and served as President of that organization between 1916-1918. The Society awarded him the Murchison Medal in 1907 and their highest honour, the Wollaston Medal in 1922.

In 1935 he was awarded the Royal Medal of the Royal Society (Fellow since 1902).

The University of Edinburgh awarded him with an honorary doctoral degree in law in 1919, as did McGill University. Harker Glacier on South Georgia Island, Mount Harker in Antarctica, and Dorsa Harker, a feature on the Moon, are named after him. The mineral harkerite, first found on the Isle of Skye, is also named after him. Ternary composition plots used in classifying igneous rocks are commonly referred to as Harker Diagrams.

Harker retired in 1931 and was made Honorary Curator of the Cambridge Petrological Museum, and their extensive rock collection bears his name. St. Johns College made him a Life Fellow soon after his retirement. Alfred Harker died in 1939.

A book illustrating the geology and landscapes of the Western Isles of Scotland was published post-humously. Many of the illustrations in this work were based on drawings he made in his numerous field notebooks.