https://www.everglades.org/early-formation/ >Only about 5000 years ago did South Florida’s climate take on its current sub-tropical and monsoonal character of dry winters followed by hot moist summers with large amounts of rain (on average 50-60 inches per year), as seas that surround it on three sides warm and evaporate.

The Amazon rainforest itself is also not that much older than 10k years. In fact, there's some evidence that humans played a major role in its transition from grassland to jungle

The unique ecosystems and their locations around the world are a direct consequence of the oceans and weather. The oceans and weather were wildly different during the last ice age and consequently the ecosystem present in many places was wildly different than it is today.

Even only going back a couple thousand years the changes have been huge (desertification in the ME and North Africa).

Thats when the sea receded, so its "only" 5,000 years old after all.