Most of us weren't aound at the time but we can try to piece together the puzzle.
if the hadith is factual and the final messenger of Allah pbuh really did say it, then it is true.
If it is true, then we can theorize that not only humans, but trees and animals were possibly also larger, the earth would have been less polluted, the soil fresh, the food highly nutritious , there are ahadith that say that after the post drought rain after dajjal, the earth will be like new again and a pomegrenate peel will be like an umbrella, Allah knows best, maybe some scientific research would help shed light on the topic but not much unless we get a closer estimate of when Adam appeared as man.
It is unlikely that creatures before him had the intelligence to build sewage systems and to drain waste nutrients into the rivers lakes and oceans, so the sum total depreciation of ground nutrients would be nearer to zero before man appeared.
They say africans were amongst the first, and they're huge in comparison to the chinese and narive indians who must've migrated outwards in later generations.
The vast differences in the human species and it's evolution is also an indication that we're nearing the end of our term.
