The age of the Earth has been determined through the decay of isotopes and has been found to be about 4.5 billion years old.
Doesn’t this assume that the atoms from which the age is determined originated when the solar system was born. If our Sun was a third generation star then clouds of gas from which our solar system formed were rich in heavy metals formed in the cores of preceding stars.
If the elements had been formed much earlier, wouldn’t the Earth been a heck of a lot younger.
I am not a creationist and do not doubt the Earth is that old, I just want an explanation.
There are actually 4 or 5 seperate lines of evidence that all point towards the same time period, and it isn’t reliant on one single source. If no one else can elaborate more on that, I will try to look up more info.
This is a good start. Mostly geared towards debunking young earth creationism.
The assumption is that the rocks being dated have remained unchanged since they were laid down as part of the Earth. The dating compares the amount of, say, Uranium to Lead in a sample. If you can make assumption about the original composition and assume that no Uranium or Lead were added or removed, then you get a date. Very old dating is often done with crystalline structures that would be impervious to water.
Carbon dating works nicely because it appears that the levels of C-14 produced in the atmosphere are approximately constant throughout history, thus we can presume to know the original ratios as laid down in a particular point in time, such as the point when wood was grown by a living tree. Obviously, carbon dating is worthless for dating the age of the Earth, but it’s a good example because it’s obvious where we get our knowledge about the original ratios.
Different kinds of materials tend to be segregated somewhat within the Earth. So, for instance, when the Earth formed, it already had some lead and some uranium, but they probably wouldn’t have been mixed together very much. So if you find some uranium ore right now, and it’s got lead in it too, that lead was probably formed by the decay of the uranium, not primordial lead.
I never thought of that but:
How do they know that they probably would not be mixed together very much?
The minerals you use for dating don’t incorporate any of the daughter isotope into their crystal structure, so you know that any of these isotopes which are present were the result of post-crystallization radioactive decay. For example, in the U-Pb dating that is used to date really old rocks, they usually use zircon which incorporates uranium but not lead.
It’s the ratio of isotopes within particular rock samples that provide the dates, not the ratio of isotopes within the Earth at as a whole.
Once a particular rock solidifies out of molten magma, the amount of uranium (for example) within it is fixed. It doesn’t matter that the uranium itself may have been formed billions of years earlier in a star; all that matters is the amount within the rock when the rock formed.
The age of the rock is determined by how much of the uranium contained in it initially has decayed into lead. (Whether the lead is primordial or derived from radioactive decay can be told from its isotope number; Lead 204 is primordial; Lead 206, 207, and 208 are the products of decay of other elements.) If there is a lot of uranium relative to its lead decay products, the rock is young; if most uranium has changed to lead the rock is old.