The young-earth concept – that the earth is less than 10,000 years old – is totally out of synch with modern science due to a misunderstanding of the single Hebrew word yō·wm, which is translated 'day' in English translations of the Bible.
In most instances, yō·wm means a 24-hour day simply because that's what's meant most of the time it's used. But yō·wm is a flexible word so that, when the conversation was about an indefinite time, the word is understood from the context to refer to a longer time.
Yō·wm was used in the Hebrew language the same way we use 'day' in our English language.
'Day' to us usually means 24 hours, but sometimes we say things like, 'In the day of sailing ships ...' or 'In his day ...' or 'This is the day of social media ...' or 'At the end of the day ...' The reader knows from the context what we mean.
For example, here's how yō·wm is used in another passage in the Old Testament:
Tap HERE to see the Hebrew>English Interlinear Bible showing the word usage in Genesis 1. Tap HERE to see the Hebrew>English Interlinear Bible showing the word usage in Micah 7. The same original Hebrew word yō·wm is used in both passages, so therefore that word in scripture does not always mean 24 hours.
So the question is: Why do some Christians say that yō·wm as used elsewhere, as in Micah 7, can mean a long indefinite time but cannot have that meaning in Genesis 1? There is no reasonable answer except long tradition.
A rule of translation is that if a word or phrase can have two or more meanings, select the one that best fits the context of the surrounding passages.
The context within the creation story itself gives many clues that 'day' means longer than 24 hours. For example:
Another clue is Genesis 3:6 in the creation story, referring to Eve: 'She also gave some to her husband, who was with her, and he ate it. Then the eyes of both of them were opened and they realized that they were naked ...' We know from the context that they were not blind and that the phrase 'eyes were opened' means that they received new spiritual understanding.
The Apostle Peter acknowledges that 'day' can be used as a time variable: 'But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day' (2 Peter 3:8).
The Bible is its own best interpreter. To read the Bible objectively – to distinguish what the Bible actually says from what tradition says – it's important to read related passages together from several different translations of the original Hebrew or Greek text.
Fortunately, today's Internet gives everyone instant access to a vast library of Bible documents without registration or cost. For depth of study, you can read the Bible from interlinear versions from Hebrew-to-English or Greek-to-English, and for the breadth of study, you can read the Bible in parallel from dozens of English side-by-side versions.
This makes it possible for people today to read and understand the Bible themselves rather than just accept what others say about it.
Generally, ancient languages did not have huge vocabularies and were not as precise and nuanced as modern languages. Word meanings were often defined by the context in which they were used.
See these resources for deeper research into the meaning of yō·wm:
Centuries ago, the young-earth concept became a part of church creeds. For example, the Westminister Confession (written 1647 but still extensively used) states that the earth was created 'in the space of six days.'
Whenever a concept becomes embedded in the formal doctrine of church denominations and seminaries, it becomes heresy within that group to even question it, even in light of new knowledge, and the doctrine is defended based on tradition rather than what the Bible actually says.
Today we can understand the Bible better than at any other time in history because we now have a massive amount of scholarly information from historical manuscripts, linguistics, archaeology, and cosmology not available to early church fathers.
Except for the correct but misleading way the word yō·wm is translated 'day' in modern English, there is nothing in the Bible or science to even suggest that each of God's six major creative processes was a time equal to 24 hours in our modern calendar.