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.
Ruthenium
Fifteen other radioisotopes have been characterized with atomic weights ranging from 89.93 u (Ru) to 114.928 u (Ru). Most of these have half-lives that are less than five minutes except Ru (half-life: 1.643 hours) and Ru (half-life: 4.44 hours).