Radioactive decay dating rocks
Both carbon-12 and carbon-13 are stable, but carbon-14 is unstable, which means that there are too many neutrons in the nucleus. As a result, carbon-14 decays by changing one proton into a neutron and becoming a different element, nitrogen-14 (with 7 protons and 7 neutrons in the nucleus).
The isotope originating from the decay (nitrogen-14 in the case of radiocarbon) is called the daughter, while the original radioactive isotope (like carbon-14) is called the parent.
The biggest assumption is that, to first order, the number of asteroids and comets hitting the Earth and the Moon was the same as for Mercury, Venus, and Mars. The bottom line is that the more craters one sees, the older the surface is.
This can be interpreted in two ways: why it is important to know the age of a planet or how is age dating important in determining the age of a planet?
Once the half life of an isotope and its decay path are known, it is possible to use the radioactive decay for dating the substance (rock) it belongs to, by measuring the amount of parent and daughter contained in the sample.
An important point is that we must have an idea of how much of the daughter isotope was in the sample before the decay started.
This is also a way to get at the abundance of the various isotopes of carbon.
Based on our study of meteorites and rocks from the Moon, as well as modeling the formation of planets, it is believed (pretty much well-established) that all of the objects in the Solar System formed very quickly about 4.56 billion years ago.
When we age date a planet, we are actually just dating the age of the surface, not the whole planet.
This may simply have to do with what the media is talking about.
When there is a scientific discussion about the age of, say a meteorite or the Earth, the media just talks about the large numbers and not about the dating technique (e.g. On the other hand, when the media talk about "more recent events," ages that are more comprehendible, such as when early Man built a fire or even how old a painting is (or some ancient parchment), then we bring up the dating technique in order to better validate the findings.