How old is the Earth?

“In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move.” (Douglas Adams The Restaurant at the end of the Universe)

The question “How old is the Earth?” has provided us with some pretty interesting, often rancorous and even divisive debates over the last few hundred years.  For some the debate remains unresolved.  The science of dating things has progressed hugely over the last century and we can now provide, with significant confidence both relative age (A is older than B) and quantitative ages (radiometric dating) for all manner of physical objects.  Age dating of earth materials is not just an interesting academic exercise; it has provided us with the tools to help evaluate energy and mineral resources, to assess the risks from natural hazards, and to study past geological events as they may relate to our future well-being.

So where do we begin?  Perhaps at the beginning.  Present estimates for the Big Bang and the formation of the Universe are about 13.8 billion years ago. We now know that our own Solar System began to form about 4.6 billion years ago which means there is an hiatus of 9 billion years. What happened during that great ‘interregnum’ is another story (how many other Solar Systems?).  Our tale begins 4.6 billion years ago because that is closest to home.  In this post we will be focusing on the bottom end of the time-line shown below. Continue reading →