Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
Some of the isotopes used for this purpose are uranium-238, uranium-235 and potassium-40, each of which has a half-life of more than a million years.
Unfortunately, these elements don't exist in dinosaur fossils themselves.
limestones), huge quantities of atmospheric carbon dioxide end up locked away for a very, very long time.
The process begins when CO (or carbonic acid - the old name for carbon dioxide was carbonic acid gas) Rainwater containing carbonic acid is able to react with most minerals at varying rates according to their chemical stability.
The compounds making up the vast majority of Earth's land surface - the minerals that make up rocks - are, by and large, very slow to react.
As a consequence, large-scale weathering is a process that takes place on a timescale of millions of years, over which periods it constitutes a critically important carbon-sink. Because, via weathering of rocks and reprecipitation of weathering products as carbonate sediments (e.g.
But this sediment doesn't typically include the necessary isotopes in measurable amounts.
Fossils can't form in the igneous rock that usually does contain the isotopes.
All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. This post delves into the long-term carbon cycle that involves the interactions of the atmosphere with rocks and oceans over many millions of years.