Baron Gerard Jacob De Geer ForMemRS[1] (20 November 1858 – 24 July 1943) was a Swedish geologist who made significant contributions to Quaternary geology, particularly geomorphology and geochronology.

[3] Baron Gerard Jacob De Geer comes from a well-known Swedish aristocratic family of Brabant origin, who had emigrated to Sweden in the early seventeenth century.

[8] In 1882, on the recommendation of Otto Martin Torell, de Geer participated in the Swedish expedition to Spitsbergen as part of the first International Polar Year as a staff geologist.

[10] The pinnacle of de Geer's scientific career can be considered the receipt of the presidency of the X International Geological Congress, held in Stockholm in 1910.

In addition, before the start of the Congress, De Geer conducted an excursion for 65 delegates from 14 countries, within the framework of which he examined the Dicksonfjorden on Spitsbergen.

De Geer called these annual sedimentary layers varves and throughout the 1880s further developed his theory, publishing a brief outline of his discovery in 1882, which he followed with a presentation to the Swedish Geological Society in 1884.

With the help of numerous students from both Stockholm and Uppsala, De Geer began to piece together short, but overlapping, varve sequences in south east Sweden to create a longer year-by-year chronology of glacial retreat for the Lateglacial period.

Estuarine sediments exposed along the valley of the Angermanalven River, allowed De Geer to further extend the chronology into the early Holocene.

This first attempt at long-distance correlation marked the start of two decades travelling around the world by De Geer and his colleagues, searching out varve sequences for potential teleconnections.

De Geer felt his position was being caricatured and intentionally misunderstood by Antevs, but did little scientifically to rebuff the criticisms levelled at him.

Almost immediately after the publication of Geochronologia Suecica Principles De Geer's Swedish Time Scale underwent the first of many revisions, as other geologists became involved in the study of varves and more sites were examined.

[13] The Swedish Antarctic Expedition (1901–1904) named a glacier on South Georgia Island in the southern Atlantic Ocean after De Geer.

[14] De Geer's most significant contribution to Quaternary science was unquestionably the identification of varves, and his recognition of their potential in establishing annual chronologies of past climatic and environmental change.