Nonfiction passages that are organized chronologically often contains dates. Events are told in the order in which they happened, and the author uses time-order words, such as first, second, next, and finally to make a sequence of events clear.
Another important clue are words like meanwhile and simultaneously which signal that two or more events took place at the same time.
And finally, the author may include dates and other information of time called time indicators to help readers understand the relationship of events happening in the text.