If “liberal Christianity” means Christianity that reflects the cosmology and worldview of a particular era, then the earliest Christianity is liberal Christianity. It is only later, as cosmologies and worldviews changed, that some insisted on clinging to the views of an earlier era, because those happened to be part of the worldview of previous generations of Christians, including the Bible’s authors. That is why “conservative” Christianity ends up being a very radical departure from earliest Christianity, even in the process of fighting to try to keep the same worldview as they had to the minimal extent that that is even possible. By making the assumptions of prior generations into articles of faith, they stand against and not with the approach of the earliest Christians, even while claiming to defend their specific beliefs.
If liberal Christianity means one that elevates orthopraxis over orthodoxy, then we can see that in our earliest sources too.
And so the irony is that conservatives berate liberals for departing from the “historic truth,” and yet liberals are closest in their approach to Christianity in its earliest known form.