Roger Tsien, co-winner of the 2008 Nobel Prize in chemistry and professor of pharmacology, chemistry and biochemistry at University of California San Diego School of Medicine for 27 years, died Aug. 24, 2016 in Eugene, Ore. He was 64.

UCSD officials said Tsien died on a bike trail. The cause of his death hasn’t been determined.

With Osamu Shimomura, PhD, an emeritus professor at the Marine Biological Laboratory in Woods Hole, Mass. and Martin Chalfie, a professor of biological sciences at Columbia University, Tsien helped scientists peer within living cells and organisms as never before, earning not just the 2008 Nobel Prize but scores of subsequent awards and accolades.