The major division on geologic time that came first is the Precambrian Supereon.

Here's why:

* Geologic Time Scale: The geologic time scale is a system used by geologists to represent Earth's history. It's divided into eons, eras, periods, and epochs.

* Precambrian: This supereon encompasses the vast majority of Earth's history, spanning from the formation of the planet about 4.5 billion years ago to the beginning of the Paleozoic Era, about 541 million years ago.

* Paleozoic, Mesozoic, and Cenozoic: The other three major divisions – the Paleozoic, Mesozoic, and Cenozoic Eras – all occur *after* the Precambrian.

So, the Precambrian Supereon is the earliest and longest division of geologic time.