Is it possible that the Australian aboriginals were not the first humans here?

We already have good scientific evidence that the Australian Aboriginals where the first people ANYWHERE, outside of Africa.

It doesn't leave much time for humans to have left Africa, and arrived in Australia, before the first Aboriginals got here. So, who would be expecting to have lived here first, BEFORE the Aboriginals?

Unless you want to go back to the Multiregion hypothesis, and argue that Homo erectus evolved into Homo sapiens here in Australia (or possibly in Indonesia). The Out-of-Africa vs Multiregion dispute is still unresolved, but by far the majority opinion today has swung behind the Out-of-Africa hypothesis.

It's notoriously difficult to prove that an unproven thesis is impossible (compared to proving that it is possible). But unless some kind of substantive evidence turns up - from genetics, fossils etc - then there is no reason to support the idea Aboriginals were not the first humans in Australia.

Hope it helps.

By "here" I take it you mean "in Australlia"? Hard to say... I don't think it would be exactly Earth-shattering to learn that the peoples we now call Aboriginals followed some earlier population...

its possible. no implications. nobody cares about aboriginals, equally nobody would care about pre-aboriginals.