How do we know the age of the earth?

Scientists generally determine the age of the Earth based on radiometric age-dating of fragments from the Canyon Diablo iron meteorite. From the fragments, scientists calculated the relative abundances of elements that formed as radioactive uranium decayed over billions of years.

Tropical climate is experienced in the nothern countries of south america

It is useful for historians to write narratives so that history can be passed on from their point of view.  think about a story being told in third person, then think about it again being told in first person, by someone who actually experienced the event.