In Jain cosmology, the six aras of the current Avasarpiṇī kāl are usually described like this:

1. Susham-Susham Ara — life span is 3 palyopam
2. Susham Ara — life span is 2 palyopam
3. Susham-Dusham Ara — life span is 1 palyopam
4. Dusham-Susham Ara — life span starts very long and gradually decreases; in the common human-age scale it is said to range around 84,000 years
5. Dusham Ara — life span is much shorter, traditionally around 21,000 years
6. Dusham-Dusham Ara — life span is the shortest; traditionally around 1,000 years or less, depending on the scriptural explanation

A simple way to remember it is:

• First 3 aras: measured in palyopam
• Last 3 aras: measured in years, with life span steadily decreasing

If you want, I can also give you the duration of each ara and the exact Jain traditional classification in a neat table.