It is often said that the greatest deceit of the devil is convincing people he doesn't exist. However, as great a deceit as that is, the actual greatest deceit the devil has ever pulled off is convincing people that regardless of whether he exists or not, God is not to be trusted.
For thousands of years, he has been pulling this same trick, but he often uses different methods. Most famously, he deceived Eve, twisting God's words, before telling her they're not true. The result? The first ever sin, which brought death into the world. Since then, he has remained our enemy, deceiving human beings, whether they believe in the Lord or not.
In the modern world, this deceit takes many forms. False religions and philosophies, empty pleasures, unfounded fears, these are all weapons the devil expertly wields to draw people away from God. Even when he fails to draw us away from God, he will do what he can to trip us up in our walk with Him.
Twisting God's word and casting doubt upon it is, as it has always been, his go-to, and one way in which he does this, strangely enough, is by exaggerating the age of the heavens and the earth. While it is an apparently small issue, it turns out to be as trivial as the difference between "You shall not eat of every tree of the garden" and "Of every tree of the garden you may freely eat; but of the tree of the knowledge of good and evil you shall not eat".
This one little issue carries many implications, starting with the very authority of God's word. See, although the Bible never says "the Earth is 6,000 years old", it does give us a number of ways to determine roughly how old it is. It does not do this so precisely as to tell us the hour, the day, or even the year, but with reasonable accuracy, we can determine the age of the Earth.
To do this, we first need to ask, when the Bible says "In the beginning God created the heavens and the earth" (Genesis 1:1), when was this? Of course, I don't mean it's as simple as the very next verse saying "this happened in 4004 B.C." That would be useful, but also silly. What's even sillier, however, is the so-called "gap theory".
Gap theory, as the name suggests, is the theory that there is a gap somewhere in Genesis 1 that allows us to fit the millions of years required for things like Evolution to have taken place. In particular, it posits the idea that the single space between Genesis 1:1 and Genesis 1:2 is where the gap exists. Some particularly pious compromisers even suggest that Genesis 1:2 should be rendered "The earth became without form, and void", rather than "The earth was without form, and void..." (emphasis added) as it appears in every reputable English translation. There is simply no justification within the text to render it as "became", nor indeed to believe there is any kind of gap between Genesis 1:1 and 1:2.
The most obvious interpretation of verse 2 is that, being the beginning of creation, the Earth was without form and void because it was as yet in an unformed and unfilled state, rather than that, as some speculate, there was a huge expanse of time between the initial creation, and then some chaotic event (such as Satan's rebellion) that required it to be repaired.
This interpretation is further backed by the fact that after telling us this, God proceeds to create literally everything else, first forming everything on days 1-3, then filling them on days 4-6. Of particular note is that this includes, of all things, the sun. Having formed the light on day 1, God then created the sun and moon to serve as signs, and give light to the earth. No sane person is going to posit the idea that there were dinosaurs living millions of years ago, but they were running around in utter darkness, with no sun to heat the world or feed the plants they would need to sustain their eco-system.
Unless you desperately want to extend the age of the Earth, there is no gap in Genesis. There is simply a span of 6 days between God's initial act of creation and the ultimate cessation of His creative acts. The culmination of those acts? "So God created man in His own image; in the image of God He created him; male and female He created them. (...) Then God saw everything that He had made, and indeed it was very good. So the evening and the morning were the sixth day." (Genesis 1:27, 31).
On the 6th day of history, God created human beings. And not, as some suggest, a great many of them, only for Him to choose Adam out of them, plop him in a garden with his wife, then one day, they bear Cain, and after killing his brother, he heads off and finds a bunch of other people in some city somewhere. No, Genesis 2 zooms in on day 6, and details just how the creation of Adam and Eve went down.
These truths are actually quite foundational to later Biblical doctrines. Both the doctrine of the Sabbath, and the doctrine of marriage, find their origins and foundations in the creation account. Exodus 20:9-11 tells us "Six days you shall labor and do all your work, but the seventh day is the Sabbath of the Lord your God. In it you shall do no work: you, nor your son, nor your daughter, nor your male servant, nor your female servant, nor your cattle, nor your stranger who is within your gates. For in six days the Lord made the heavens and the earth, the sea, and all that is in them, and rested the seventh day. Therefore the Lord blessed the Sabbath day and hallowed it."
You see, then, that one of the famous 10 commandments depends entirely on the creation account being a real, historical, literal event. It wasn't some silly diss track on the pagans (although it certainly offers a powerful rebuke to those "who exchanged the truth of God for the lie, and worshiped and served the creature rather than the Creator, who is blessed forever. Amen." (Romans 1:25)). It isn't some allegory whose true sense has been lost to time. It isn't a poem, lost in translation. Put simply, if the Old Earthers are right, we lose the Sabbath.
We also lose marriage. Twice in the New Testament, once in Matthew 19 and once in Mark 10, Jesus is questioned regarding the legitimacy of divorce. To defend His answer, He not only refers back to the creation accounts, but also links them, saying, in Matthew 19:4-5 "“Have you not read that He who made them at the beginning ‘made them male and female,’ (Genesis 1:27) and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh’? (Genesis 2:24)."
We are seeing the fruits of this compromise in our own culture. Having got rid of Genesis, we have quickly become Satan's playground. We now live in a world where God did not make man male and female, but "cisgender" male, "cisgender" female, transgender, cake gender, and umpteen other made up genders, all depending on how one happens to feel at a given time.
And who says marriage has to be when a man leaves his father and mother and bonds with his wife to become one flesh? Heck, we are now approaching the days when one doesn't have to be considered old enough to leave their parents before engaging in marital acts. Not that we didn't already have a problem with that anyway, what with teenage pregnancy and the like, but we've always seen that as a problem, not an act to be celebrated.
Of course, not every old Earth position denies the historicity of Adam and Eve. In fact, the age of the Earth doesn't make any direct impact on these accounts. It could have happened 7,000, 8,000, 10,000, even 100,000 years ago, and as long as it all went down the exact same way, you would have exactly the same foundations.
If it weren't for those meddling genealogies...
See, the way we know the age of the Earth is that the Bible does tell us. Using Adam, who is only 6 days younger than the Earth, as a benchmark, if we can figure out how old he is, we can figure out how old the Earth is. And we can figure out how old Adam is, since the Bible gives us his genealogical history in painstaking detail.
Beginning in Genesis 5, Adam is noted to have lived 130 years before having a son, named Seth. That means Seth is 130 years younger than the Earth. After this, Seth has a son of his own, Enosh, when he is 105. Now, we measure our age in years, even up until the very day of the next. Thus, it's possible Seth was born a day before Adam's 131st birthday. It's equally possible he was born a day after Adam's 130th. The same principle applies with Seth and Enosh. Thus, each successive generation increases the margin of error by 364 days. However, there are nowhere near enough of these generations to give us an age for the Earth much greater than 6,000 years.
Of course, Genesis 5 doesn't give us a complete record of Adam's descendants. It only goes up to Noah, who has his three sons at around 500 years old. But then Genesis 11 picks up on Shem's genealogy, going from his son, Arphaxad, whom he begot at age 100. This leads us to Abram, who would go on to become Abraham. And of course, Genesis continues to follow him, his son Isaac, his son Jacob, his 12 sons, concluding with them in Egypt. And if you don't know how to follow the history from there, you really need to pick up your Bible more often.
So with all of this combined, we can trace Adam's lineage all the way up to Jesus, who of course was born roughly 2,000 years ago. Skipping over the math, which most of us tend to do anyway, we get a rough age of 6,000 years for Adam. And of course, if today was Adam's 6,000th birthday, then the Earth would be exactly 6,000 years and 6 days old.
This is quite comprehensive. You can't get around this age without seriously fiddling with the text in unholy ways. In fact, doing so makes it clear that you are committed not to learning from Scripture, but forcing a conclusion into it. At that point, you can do anything with it. You see, then, how if you lose the age of the Earth, you lose a whole lot more.
By far the greatest implication for the age of the earth is the origin of death. The Bible tells us plainly that this is sin. When Adam sinned, he brought death into the world. Even ignoring every piece of evidence we have looked at today, even if we genuinely did not know how or when God created the heavens and the earth, we must emphatically reject the existence of death before sin.
Yet, if there truly was some kind of gap in Creation allowing millions of years, there was plenty of death before sin, including 5 mass extinctions. Adam himself would have been descended from billions of dead things, dead humanoid things (for only humans produce humans). We even find fossils of thorns, which are quite explicitly said to be a part of the curse following The Fall.
The logic just doesn't fit. You either have man before sin, as the Bible says, or death before sin, negating the need for a savior. Thus, if we add millions of years before Adam, we lose the last Adam! Jesus, who took the fullness of the curse upon Himself in the Garden of Gethsemane, would have had no need to do so if death was just the natural, and I'll add "very good" course of things.
Let no man deceive you: The age of the Earth is a very important issue. Without it, the clarity, and even the authority of God's word gets called into question. And just as the first human couple rebelled against God, bringing death into the world, when this was done for them, it will wreak havoc on your spiritual life, this world, and maybe even your own soul, if it is done for you.