Many people believe the earth is billions of years old; the Bible tells us that God created it in six days. Some Christians try to reconcile these two beliefs by saying that the days of creation aren’t literal days but simply long periods of time.
The word “day” can mean an indefinite time period and it is used that way in the creation account.
These are the generations
of the heavens and the earth when they were created,
in the day that the LORD God made the earth and the heavens.
Here the entire time of creation is called a day. But what about the days in the first chapter? Here is a description of the first day.
And God said, “Let there be light,” and there was light. And God saw that the light was good. And God separated the light from the darkness. God called the light Day, and the darkness he called Night. And there was evening and there was morning, the first day.
Each day included a period of light and one of darkness and consisted of an evening and a morning. Only a literal day consisting of the time the earth turns once on its axis has these characteristics.