Something very old and something really old.

First appearing over 3 billion years ago, stromatolites are the oldest known fossils. They were colonial structures built by photosynthesising blue-green algae, and were responsible for the creation of earth's oxygen atmosphere. These organisms thrived in warm aquatic environments, building reefs much as corals do today.
The photograph is a slice through a relatively young, 120 million year old, stromatolite from the Mendip hills.
Sitting on top of the stromatolite is a fossilised piece of dinosaur bone from what is now Wyoming in North America. Dinosaurs went extinct about 65 million years ago (at the end of the Cretaceous Period), after living on Earth for a mere165 million years.