And what we read in the Bible is confirmed by the observations we make in the world around us.
There is absolutely no way any scientist can know whether these two assumptions are correct, because the evidence only exists today in the present, and we can’t go back to test the past millions of years and check that the rates of radioactive decay were the same then as they are now. This notion is based on a complete misunderstanding of the nature of evidence.
In our three article series on radiometric dating, we discuss in depth the assumptions that scientists must make.
For example, it has to be assumed that all the daughter isotopes found in rocks today have been derived by radioactive decay of the parent isotopes.
If you did, you'd know about radiometric dating and how it is used as irrefutable proof that the Earth by itself is approximately four billion years old. Yes, we are well aware that there are different radioactive isotopes and that they can be used via the technique of radiometric dating to date materials from bone fragments to rocks. From the way you are using the word, it does not seem that you understand its meaning.
In a courtroom, the “proof” that is sought by the judge and the jury is corroborated testimonies from eyewitnesses who were present at the scene of the crime and who saw the accused perpetrate the crime.
He is not capricious but has put order and regularity into His creation, and He is a reliable eyewitness of what happened in the past as recorded in the Bible.