These periodic changes on Earth are a result of the five major that have occurred throughout Earth's history.

According to the federal regulations, which of the following studies meets the definition of research with human subjects? a study of twenty 4th grade classrooms in which researchers ask the schools to systematically vary the time of day reading is taught, and collect weekly assessments of reading comprehension for each child over a three-month period.the collection of data, by a playground designer hired by the superintendent of schools, about the physical dimensions of school playgrounds, presence of fencing, and the kinds of equipment currently provided.a feasibility study for implementing a year-round school program, focusing on economic issues such a facilities utilization and transportation costs.an analysis of aggregate data comparing statewide high school graduation rates provided by the state department of public instruction, using county tax information.

Push-and-pull factors contribute to

Imperial crisis inflation invasion pax romana great schismtrade during the , roman generals warred over succession. these conflicts drew soldiers away from the frontier and made the empire vulnerable to