It's important to note that this is a broad range, and different species of Australopithecus existed at different times within this period. For example:

* Australopithecus afarensis (the species of "Lucy" the fossil) lived from about 3.9 to 2.9 million years ago.

* Australopithecus africanus lived from about 3.3 to 2.1 million years ago.

* Australopithecus sediba lived from about 2 million to 1.8 million years ago.

So, while the overall time frame is around 4.2 to 2 million years ago, specific species had more limited time ranges within that period.