I meant, they sink and get buried in sediments. I thought drowning means also that. But, “drown” means also “die through submersion in and inhalation of water”. I didn’t mean that for example bones die.
That is not the meaning of the word "drowned". Not all sediments are marine or even lacustrine. Some of them are aeolian. Flood believers have no explanation for that. Their beliefs are also refuted by salt deposits in the middle of a "flood". Layers with millions of years of annual deposits that leave layers very similar to the rings on a tree. Chalk. And countless other examples. You cannot refute that which you do not understand.
That they make assumptions is said even in here:
“Previously, when applying the alternative Pb–Pb isochron diagram, the 238U/235U isotope ratios were assumed to be invariant among meteoritic material.”
Lead–lead dating - Wikipedia
LOL! No, you got that 100% wrong. They used to have to assume that. The next few lines explain a work around. And you need to understand that scientists often use a different definition of "assume" than you are. If a scientists says "assuming this" they need to be able to justify that assumption. In your sense of using it to attack an idea they are not "assuming".
"To accommodate this, U-corrected Pb–Pb dating analysis is used to generate ages for the oldest solid material in the solar system using a revised 238U/235U value of 137.786 ± 0.013 to represent the mean 238U/235U isotope ratio bulk inner solar system materials.
[4]
The result of U-corrected Pb–Pb dating has produced ages of 4567.35 ± 0.28 My for CAIs (A) and chondrules with ages between 4567.32 ± 0.42 and 4564.71 ± 0.30 My (B and C) (see figure). This supports the idea that CAIs crystallization and chondrule formation occurred around the same time during the formation of the solar system. However, chondrules continued to form for approximately 3 My after CAIs. Hence the best age for the original formation of the solar system is 4567.7 My. This date also represents the time of initiation of
planetary accretion. Successive collisions between accreted bodies led to the formation of larger and larger planetesimals, finally forming the Earth–Moon system in a giant impact event"
If I have understood correctly, the idea of that is, radioactive isotope decays in certain rate and by checking how much radioactive isotope there is left and how much non-radioactive isotope there is, we would calculate the age of the sample. Now, that assumes that there was not originally any non-radioactive isotope in the sample. However, it is possible that there were originally also non-radioactive isotopes, which is why the method can’t be trusted.
No, that is never the assumption. Now in some cases it is a reasonable conclusion. For example when dating zircons it is reasonable to assume that there was no significant lead in the crystal to start with. Do you know why? It is not an assumption in the sense that you are using the word.
