How do historians identify one era as separate from another era

By putting the clear limits between two eras, which are usually indicated by some important events or some changes that totally changed the society and mankind.

Explanation:

To easily examine historical eras it is important to put clear limits between eras. For example prehistory ended and history when the first states were created and the written letter appeared. This was a great change, that totally changed the human kind. It was something new, totally different, that affected everyone. That is why this two period are indicated like that. Period without states and written letters (prehistory) and the period that had these (history).

for starters, there is the structural trend of rising primary government expenditure as a share of gdp, which reached 36% in 2014, up from 22% in 1991. this increase reflected a political desire to address the poverty and inequality that had gone unaddressed during previous decades. to support the increase, brazil’s government increased taxes on consumption and promoted progress toward labor-market formalization. nonetheless, public investment, particularly in infrastructure, took a hit. in fact, with the exception of the 2005-2008 period, total investment as a share of gdp has remained below 20% since 1991.

name two ways organisms join a population and two ways organisms leave a population. two ways organisms join a population are birth rate and immigration. two ways they leave are death rate and emigration.

explanation: