When did the dinosaurs live?

Most people know that dinosaurs lived a long time ago but they're usually not sure when exactly. Well, dinosaurs live during a time called the Mesozoic Era. Mesozoic means "middle life". Given the name because is lies between the Paleozoic ("ancient life") and Cenozoic ("new life") Eras. These eras lie in the Phanerozoic Eon. This period of time makes up part of what is know as the Geologic Time Scale.  Before the Phanerozoic Eon was the Precambrian Eon. The Precambrian Era starts at the earth's creation and goes to a time where hard-shelled animals were first forming.

Since we are concerning ourselves with dinosaurs, we will concentrate mainly with the Mesozoic. The Mesozoic was further broken down into three periods. These were, from oldest to youngest, the Triassic, Jurassic, and Cretaceous. The Triassic and Jurassic were further broken down into Early, Middle and Late Epochs. The Cretaceous was broken down into Early and Late Epochs. These were all broken down even further by their unique rock formations. These were categorized as  Upper, Middle, and Lower.

The Mesozoic lasted approximately 180 million years. The Triassic from 248-213 million years ago (mya). The Jurassic from 213-144 mya. The Cretaceous from 144-65 mya. So, add that all up and you can see that dinosaurs had survived for around 180 million years. To get an idea of how long that is, Homo sapiens (modern man) has been around for around 200,000 years. Recorded history, around 10,000. These estimate tend to change with each new discovery, and they depend on different criteria for "modern man".

So, you can see that dinosaurs may be gone, but they were around a lot longer than we have been so far. That's why I wonder why so many people say dinosaurs were failures and anything old or antiquated is always called a "dinosaur". They were a very successful group who's course had run out. Some scientist say they were declining towards the end of the Cretaceous and without the help of a possible catastrophic meteor or volcanic activity, they would have died shortly after the Cretaceous, anyway.

Some say dinosaurs are still around today in the form of birds. A once controversial topic, it is becoming more widely accepted all the time. We will get into the dinosaur-bird theory as well as what might have ended their long reign in other topics.