I personally think the Gemmorah ad loc offers a very clear Pshat:
יכול ישאל אדם קודם שנברא העולם ת"ל
"למן היום אשר ברא אלהים אדם על הארץ"
One might have thought that a person may ask questions with regard to matters preceding the creation of the world. Therefore, the continuation of the verse states: “Since the day that God created man upon the earth,” but not earlier.
That does not mean geology or astrophysics (before 1 September 5509 BC), it just narrows the research to the beginning of the physical world, so a person would not be occupied with the philosophy of the creation - why did G-d create the world, what does He want etc.
יכול ישאל אדם מה למעלה ומה למטה מה לפנים ומה לאחור ת"ל
"ולמקצה השמים ועד קצה השמים".
מלמקצה השמים ועד קצה השמים אתה שואל ואין אתה שואל מה למעלה מה למטה מה לפנים מה לאחור.
One might have thought that a person may ask questions with regard to what is above, what is below, what was before, and what is after the world. Therefore, the same verse states: “From one end of the heavens to the other” (Deuteronomy 4:32), which is explained as follows: With regard to that which is from one end of the heavens to the other, within the boundaries of the world, you may ask, but you may not ask what is above, what is below, what was before, or what is after.
If the first statement dealt with the timely boundaries of the creation, the second statement deals with the physical boundaries of it (as it was widely accepted - the elephants, and the giant turtle etc).
You might then ask "Why were they so frightened by researching those areas?" - but it's a different question.