The image displayed below is a geological column. This is the standard means by which geologists display geological time. This column is reduced to show only the geological era called the Mesozoic. Columns with all the geological periods can be found in the recommended texts in the reference section.
The column below lists the oldest geological period, the Triassic at the bottom and the youngest, the Cretaceous at the top. The numbers alongside the column are millions of years before now. Each of the geological periods is divided up further which is what the 'Upper', 'Middle' and 'Lower' part of the column means. The short sentences on the right of the diagram give you an idea of some of the important geological and biological events that happened in that period.
If you come across a mention of period of time in one of the other pages that you want to relate to the other time periods come back to this page, or keep it open all the time, using a split screen.