Research in which existing data, such as census documents, college records, and newspaper clippings, are examined to test a hypothesis is known as

I believe the answer is: Archival research

In the past the data for Archival research could be easily accessed by public through things such such as documents on repository or books/articles kept in library. Now days, archival research could be done by everyone through the internet from the comfort of their own home.

world war i had a devastating effect on german-americans and their cultural heritage. up until that point   german-americans, as a group, had been spared much of the discrimination, abuse, rejection, collective mistrust experienced by so many different racial and ethnic groups in the history of the united states. indeed, over the years, they had been viewed as a well integrated and esteemed part of american society. all of this change with the outbreak of war.  

permafrost layer, it exists beneath a layer of soil, rock or sediment.