How do scientists know dinosaurs lived on Earth?

Like all science, you start with a thought and then add evidence until either your thought is proved wrong or as the evidence increases it is supposed to be right.

In the case of the extinction of the dinosaurs there are various things which pointed to this as an end of the dinosaurs. All around the earth in the earths crust there is a layer of 'dust'. This layer can only have got everywhere by being thrown into the atmosphere by a collision of such huge proportions as to have to be an asteroid (or indeed a comet).

A six-mile-wide (ten-kilometer-wide) asteroid is thought to have carved out the Chicxulub crater off Mexico's Yucatán Peninsula, triggering worldwide climate changes that led to the mass extinction.

More recently, there has been a second larger crater found on the Indian ocean floor. one or both of these would have been enough to wipe out the dinosaurs (