Why would a researcher use a primary source instead of a secondary source when analyzing a a historical event

Ateam of scientists studied the sediment at the bottom of an ancient lake. they were able to determine the weather conditions of the indus valley in ancient times. they found that the entire area had suffered a drought after the monsoons declined. this drought lasted 200 years. because of the drought, there wasn’t enough food or water. the people of the indus valley were forced to leave their cities.

Marine exptoration of oil uses seismic waves to locate oil in the seabed. what is a negative impact from seismic waves on the aquatic ecosystem of the ocean? a.seismic waves kill microoganisms b.seismic waves disrupts the sand and causes seafloor erosion c.seismic waves have virtually no adverse affects on marine life d.seismic waves damage the sonar that dolphins and whales use to orient themselves underwater

In at least two paragraphs, discuss the differences between the principles of republicanism and democracy. explain whether you think the united states is more of a republic or a democracy. refer to at least one example from the constitution. (10 points)