Anyone want to do some quick math? Measure the amount of decay in the rotation speed of the Earth. Now measure the amount of decay in the magnetic field of the Earth. Now calculate back 1,000,000 years.
More?
Ok, measure the rate of supernovae... now count the supernovae remnants.. calculate backward.
Measure the amount of sediment at the mouth of the major rivers on the Earth. Calculate back.
Measure the rate at which topographical features such as mountains erode. Calculate back.
The age of the Earth isn't a certain thing.
Absolutely none of your proposed calculations is in any way practical or useful for deriving the age of the earth. As BW had mentioned the rotation speed of the earth actually can be tracked back quite a ways, but relating it to "the amount of decay in the earth's magnetic field" is completely nonsensical.
BW's done a good job discussing the ones involving geology. Now let's look at this one:
Ok, measure the rate of supernovae... now count the supernovae remnants.. calculate backward.
Biggest issue: how do you even correlate this to estimating the age of the earth?
Then, how do you go about actually counting supernova remnants? The expanding shells of debris of a SNR disperse back into the interstellar medium fairly quickly, within a million years. Just compare how much the Vela remnant has spread out (exploded ~11,000 years ago), with the Crab nebula (957 years ago), and SN1987A (24 years ago).
The dead stellar cores (neutron stars, pulsars, black holes) from a SNR do of course last much longer (essentially forever) but can be quite hard to detect. A solitary black hole or neutron star can be completely invisible, as can be a pulsar if its beam does not sweep past earth. You would need to take into account the relative number of remnants you can detect versus how many are out there that you cannot.
Finally, the idea has a major flaw in that
the rate of supernovae occurrence is not constant. It is a function of how many young, massive stars there are at the given moment, which is dependent upon the rate of star formation, which is not the same from one galaxy to another, or even in one galaxy over long periods of time. As a galaxy ages there is less gas available to form new stars (since the process of star death does not return 100% of the gas back to the medium).
Galaxy interactions can also affect the rate of star formation.The age of the Earth isn't a certain thing.
Depends what you call certain. It is
very well supported.