The concept of "geologic time" doesn't really have a specific beginning point. It's more of a continuous process that started with the formation of the Earth itself.

Here's why:

* Earth's formation: The Earth formed around 4.54 billion years ago from the accretion of dust and gas in a protoplanetary disk. This is often considered the "start" of Earth's history.

* No clear "beginning": Geological processes like plate tectonics, erosion, sedimentation, and the evolution of life have been happening since the Earth's formation. There isn't a single moment where "geologic time" suddenly begins.

* Eons and eras: The geologic timescale is divided into eons, eras, periods, and epochs, but these divisions are based on significant changes in Earth's history, like the appearance of new life forms, mass extinction events, or major geological changes.

So, while we can say that Earth formed around 4.54 billion years ago, the concept of geologic time itself is ongoing and doesn't have a definitive starting point. It's a continuous process of change and evolution.