Wat are some of the things archaeologists study to gather information about early agrarian societies are

Remnants of old tools, whether they be crude stone or remaining biological matter.  The biological matter can be carbon dated, and many of the items have ended up in strata that also define their dates.

As to other information, fire construction, cave paintings, and other artifacts can illuminate many items about an early agrarian civilization.

Finally, the selective breeding of a plant can determine many what's and why's of a society.  Just as one example, the orange was originally a fruit mentioned in Chinese writings before BC became AD.  It is a bred species.

The three steps before modern english were indo-european, germanic, and old english. as peoples moved around the eurasian continent, their languages changed. throughout the ages, the languages became more specialized. as english has many germanic influences, it is easy to see how this was one of the forebears. also, old english was one of the main ancestors of the modern language, spoken in the 5th through about the 13th centuries.