Why it is Not Un-Christian to Believe in an Old Earth

When bringing up morality when debating with leftists and particularly secular leftists, pointing out the obvious fact that by believing morality to be subjective they believe moral relativism to be an absolute and by believing moral relativism to be an absolute they contradict their own moral relativism, sometimes I will get "But the Bible can't be absolute because it contains a creation narrative out of touch with the geological record."

In order to answer this objection we first need to ask the question "Who wrote that narrative?" The answer, according to Old Testament scholars, is Moses, given that it is categorized by Orthodox Jews as being one of his five books. Yes, Moses definitely had God's help, but at the same time, Moses was not God. In the New Testament, the Pharisees tried to challenge Jesus on divorce based on another book of Moses, and this was His response:

—begin quote—
“Why then,” they asked, “did Moses command that a man give his wife a certificate of divorce and send her away?”  Jesus replied, “Moses permitted you to divorce your wives because your hearts were hard. But it was not this way from the beginning.  I tell you that anyone who divorces his wife, except for sexual immorality, and marries another woman commits adultery.”
Matthew 19:7‭-‬9
—end quote—

Note the boldfaced portion of this quote. If the Israelite people's hearts were so hard that they needed a watered-down version of divine morality in order to be able to accept it without throwing a fit, then wouldn't it go without saying that they were also so dim-witted that they needed a watered-down version of the creation narrative in order to be able to understand it at all?

That seems to be profoundly the case. When people were confronted with facts that contradicted their predeterminations in the ancient world, they always threw fits. If these people had a predetermination that the Earth was young and were capable of getting triggered like SJWs if they were presented with something contradicting this predetermination, then why this creation narrative would get truncated from its original form by Moses suddenly begins to make all the sense in the world. If a fact falls on a hard heart, then it will also fall on deaf ears. So Moses, not God, is the one who presented a truncated, watered down version of the narrative: not to be accurate, but to appease the hard-hearted Israelites who would have cried foul at the idea of the earth being older than their predetermined notion of it. When Augustine challenged that predetermined idea centuries later, he was vehemently attacked for it — during Moses' time, it would have been even more difficult to convey.

With this in mind, if you stretch Genesis 1 out, then it matches exactly. First there was no matter, space, or time at all (Genesis 1:1-2), then there was light, then, about 10 billion years later, there was an Earth with water on it (Genesis 1:6-8), then continents began to peak out from an Earth that was initially 100% ocean (Genesis 1:9-10), then photosynthetic life appeared in order to add oxygen to the atmosphere (Genesis 1:11-13), then the thick Venus-like atmosphere thinned to the point where the sun and moon were both visible from Earth's surface for the first time (Genesis 1:14-19), then Cambrian aquatic life appeared (Genesis 1:20a), then dinosaurs with feathers roamed the Earth (Genesis 1:20b), and, finally, at the very end, human beings are created. There are creation narratives all over the place, but the Biblical narrative is the only one that places all of these events in this exact order.