How do was the carbon cycle most different before 1900s

I would probably say that it was most different because of the cars. The first car was released in 1885, but they weren't really popularized in America until the 1920s. So therefore, Earth's atmosphere was much better than it is now.

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.