In 1972, scientists in Gabon determined that 2 billion years ago a nuclear chain reaction had occured at the ancient Oklo uranium mine and Nuclear Power Plant. The reactions created plutonium byproduct and were artificially moderated using water.
Scientists declare themselves to be strict uniformitarians, that is, until ancient atomic reactors are mentioned and then uniformitarianism gets flushed down the toilet.
Corliss, W.R., Oklo: An Unprecedented Cosmic Phenomenon, Science Frontiers, Number 121, Jan-Feb 1999
Don't worry that the Oklo phenomenon might occur today on the earth's surface. The concentration of fissionable U-235 has fallen considerably in the last 2 billion years due to its radioactive decay.In other words, uniformitarianism is only valid when it supports mythology but when uniformitarianism contradicts mythology then it is invalid.