By taking them to dinner of course! 'Ba-dum-tss' (Sorry couldn't help it!)
Jokes aside, one of the most common questions we get about fossils is:
“How do we know how old this is?”
Short answer: it's not usually by dating the fossil itself, but by dating rocks around it.
The simplest method is known as relative dating. Rock layers build up over time, so lower layers are typically older, and layers above are younger. Find a fossil in a certain layer, and you know roughly its place in the timeline. It's simple, but effective, so long as you know the layer you're looking at.
Some other fossils are especially useful here. Creatures that lived for a short time geologically speaking, but spread widely around the world, (like ammonites and graptolites) act as index fossils, helping scientists match rock layers across different locations and dig sites.
For more precise ages, scientists use radiometric dating, which means measuring the natural decay of certain radioactive elements in igneous rock layers, often volcanic ash, above or below a fossil. This gives us actual numbers, often down to millions of years.
Put together, these methods let us build an incredibly detailed timeline of life, without needing to find a dinosaurs diary or alarm clock!
Fun fact: One of the most famous dates in fossil history is 66 million years ago, when the non-avian dinosaurs went extinct, and is known from dating a thin layer of ash and debris found all over the world. This layer also contained high amounts of iridium, rare on earth but common in asteroids, which helped determine the asteroid impact theory.
