Dr Lal's special interest in recent years has been in studying isotopic changes induced by cosmic rays on the earth and in extraterrestrial objects. He has extensively developed this broad area, which encompasses several fields in earth sciences and astrophysics. Utilizing sensitive low-level radiation counting techniques, radioisotopes produced by cosmic radiation in the earth's atmosphere were detected and used as tracers for studies in meteorology, hydrology and oceanography. He has been responsible for setting up two laboratories at the Tata Institute of Fundamental Research as national facilities, one for archaeological studies based on cosmic ray produced radiocarbon and the other for hydrological studies using natural and artificial tritium activity. He has shown that the results of studies of cosmic ray produced radioactivities in meteorites were indicative of the fact that cosmic ray intensity during the last few million years has been the same as it is today.