Koos Verstraten obtained his PhD with Prof. Pim Jungerius at the University of Amsterdam in 1978 for his thesis titled 'Water-rock interactions in (very) low-grade metamorphic shales: a case study in a catchment in the Oesling, Luxembourg'. He remained connected to the University of Amsterdam ever since. First in 1979 as lecturer of physical geography, soil chemistry and soil physics, and subsequently from 1980 until his retirement in 2008 as full professor of the Chair with the same title.

Koos developed into an authority in the field of soil science in general and soil chemistry in particular. He had a keen interest in unravelling the biogeochemical cycles of carbon and nitrogen, and their connection with soil formation and landscape evolution. He was a member of the last generation who could calculate the results of complex mineral weathering reactions and soil chemical parameters by hand. He always strongly committed himself to the chemical laboratory, embracing advanced new analytical procedures and equipment, and stimulated their application via the (young) scientists he supervised. He served as a strong coach and mentor for his PhD students and postdocs, and went out of his way to protect them from the administrative intricacies of the university, so that they could focus on their research. Also in general he served as a strong leader who competently defended the interest of his group, but also sought collaborations and synergy with others to advance the common interest of the earth sciences at the UvA in its broadest sense. He functioned among others as director of the graduate school ICG and as dean of the faculty of spatial science. Moreover, he played an important role in the transfer of the earth sciences to the new natural sciences institute IBED upon its establishment in 2000.

In addition to working hard, Koos recognized that there is more to life than work alone, and strived to combine duty with enjoyment. For instance, at the end of the working day he could often be found informally discussing science over a good glass of wine, but also played basketball at a high level. Nevertheless, he always remained involved in science also after his retirement. For instance, in 2018 he contributed to a scientific book on the Luxembourg Gutland, and in 2021 he helped design new mineral weathering experiments aimed to combat soil acidification in Dutch nature reserves.

With Koos Verstraten, we lose a very engaged physical geographer and a unique person. Our thoughts are with his family.