Uranium
Uranium-238 is the most stable isotope of uranium, with a half-life of about 4.468 years, roughly the age of the Earth. Uranium-235 has a half-life of about 7.13 years, and uranium-234 has a half-life of about 2.48 years.
For natural uranium, about 49% of its alpha rays are emitted by each of U atom, and also 49% by U (since the latter is formed from the former) and about 2.0% of them by the U. When the Earth was young, probably about one-fifth of its uranium was uranium-235, but the percentage of U was probably much lower than this.
Nuclear isomer
The most stable nuclear isomer occurring in nature is  which is present in all tantalum samples at about 1 part in 8,300. Its half-life is at least 10 years, markedly longer than the age of the universe. The low excitation energy of the isomeric state causes both gamma de-excitation to the ground state (which itself is radioactive by beta decay, with a half-life of only 8 hours) and direct beta decay to hafnium or tungsten to be suppressed due to spin mismatches. The origin of this isomer is mysterious, though it is believed to have been formed in supernovae (as are most other heavy elements). Were it to relax to its ground state, it would release a photon with a photon energy of 75 keV.