A brief historical account is presented of the progress made during th
e second half of the 20th century in the field of studies on formation
of heavy elements in nature. Results from the latest calculations on
the amounts of Pu-244 fission xenon in carbonaceous chondrites and in
lunar fines indicate that the generally accepted view that the solar s
ystem formed about 4,500 to 4,600 million years ago is in error.