The oldest comes first, and subsequent events follow on the relative dating line. Well, as the techniques and technology that geologists have used have become more sophisticated, they've been able to pinpoint dates more exactly. In fact, absolute dating assigns specific dates to rock formations and geologic events. You live in the Phanerozoic Eon. It's something geologists made up.
Deep time is the billions of years that cover the Earth's history.
Eons are the biggest. Think of them as years. As mentioned, we live in the Phanerozoic Eon, which started 570 million years ago. So, we can divide the Phanerozoic Eon into eras, periods, and epochs. In addition to the Phanerozoic Eon, there are three eons that account for most of the Earth's existence.