Peter Lonsdale, a professor and researcher of marine geology at UC San Diego’s Scripps Institution of Oceanography, died May 10, 2026, at the age of 78. Over more than five decades at Scripps Oceanography, he contributed to foundational developments in understanding of deep-sea geology, including the discovery of seafloor hydrothermal venting. Lonsdale was born on the Isle of Wight in the United Kingdom.