An examination of the Hebrew word for “day” and the context in which it appears in Genesis will lead to the conclusion that “day” means a literal, 24-hour period of time.
The Hebrew word yom translated into the English “day” can mean more than one thing. It can refer to the 24-hour period of time that it takes for the earth to rotate on its axis (e.g., “there are 24 hours in a day”). It can refer to the period of daylight between dawn and dusk. And it can refer to an unspecified period of time. It is used to refer to a 24-hour period in Genesis.
“And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day?” Genesis 1:5
It is used to refer to the period of daylight between dawn and dusk in “And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.” Genesis 1:16
And it is used to refer to an unspecified period of time in Genesis 2 “These are the generations of the heavens and of the earth when they were created, in the day that the Lord God made the earth and the heavens.” Genesis 2:4
Yom in Genesis 1:5–2:4 is used in conjunction with ordinal numbers i.e., the first day, the second day, the third day, the fourth day, the fifth day, the sixth day, and the seventh day.
We can determine how yom should be interpreted in Genesis 1:5–2:4 by comparing the context to the word’s usage elsewhere in Scripture. The Hebrew word yom is used 2,301 times in the Old Testament. Outside of Genesis 1, yom plus a number is used 410 times, almost always indicating an ordinary day, i.e., a 24-hour period.
There are a few instances where yom and a number do not imply a literal, 24-hour day. The words evening and morning together appear (38 times) most often indicating an ordinary day. The exact construction of evening, then morning, along with yom is only seen outside of Genesis 1 in one verse.
“And the vision of the evening and the morning which was told is true: wherefore shut thou up the vision; for it shall be for many days.” Daniel 8:26 This indicates a long period of time.
The context in which the word yom is used describing each day as “the evening and the morning,” suggest that the author of Genesis meant 24-hour periods. This was the standard interpretation of the days of Genesis 1:5–2:4 for most of Christian history.
In the 1800s, a paradigm shift occurred within the scientific community. This was mostly driven by hostility to religion and an effort to re-interpret observations in ways contrary to the Bible. This caused a rift in the scientific community. One side claimed that only atheism, as well as specific ideas such as an old earth and naturalistic evolution, was compatible with science. The other side, in response, attempted to denounce atheism and any possible old-earth interpretations.
The truth is that both young-earth and old-earth interpretations rely upon certain assumptions. Sincere believers debate the meaning of yom in the creation account because a case can be made on both sides. This does not diminish the importance of what Genesis teaches, regardless of whether or not a person accepts young-earth creationism.
According to Exodus 20:9–11, God used the six creation days of Genesis as a model for man’s workweek: work six days, rest one. God had man in mind even before He made us (on the sixth day) and wanted to provide an example for us to follow. God could have used six discrete 24-hour days, and He could have created everything using a process of long time periods. Based on literal biblical interpretation, the six literal days is the most accurate interpretation of the Genesis account.