Use sources and scaled timelines to investigate community change

Learning goal: Place events on timelines organized by years, decades and centuries, and use primary and secondary sources to explain how a community changed. A community's present buildings, roads and activities have histories. Evidence helps us describe those changes without assuming that the way things are now is the way they have always been.

A year is one unit of time. A decade contains ten years, and a century contains one hundred years. A timeline places earlier dates before later dates along a scale. Equal distances should represent equal amounts of time on a scaled timeline. A ten-year gap should occupy twice the distance of a five-year gap on the same scale.

Our fictional Mill Creek archive provides practice with source reasoning. Record A is an invented diary entry dated 1920: a resident describes crossing the creek on a footbridge to reach a market. Record B is an invented 1950 photograph description: a road bridge carries a delivery truck beside a pedestrian walkway. Record C is an invented museum summary written in 2020: it explains that the community's crossing changed during the preceding century. These records are teaching models, not authentic documents from an actual town.

A primary source comes from the time or direct experience being investigated. In the imagined archive, the 1920 diary is a primary source for that resident's experience and the 1950 photograph is a primary visual record of what appears in its frame. A secondary source interprets or describes earlier events using other evidence. The 2020 museum summary is secondary for the earlier bridge changes.

Source type depends on the question. The 2020 museum text could itself be primary evidence of how the museum presented history in 2020. Also, being primary does not mean being perfectly accurate or complete. A diary records a person's perspective, and a photograph leaves much outside its frame. Ask who created a source, when, for what purpose and what it can actually show.

Place 1920, 1950 and 2020 on a century-long line from 1920 to 2020. The first gap is thirty years, or three decades. The second is seventy years, or seven decades. The entire span is one hundred years, or one century. The 1950 point must lie closer to 1920 than to 2020; equally spacing the three records would misrepresent elapsed time.

The evidence supports a limited change claim: the modeled crossing includes a footbridge in 1920 and a road bridge with a walkway in 1950. It does not establish exactly when construction occurred, how every resident felt or whether the earlier crossing was removed entirely. To answer those questions, seek additional records such as dated plans, newspapers or more photographs.

Worked source comparison: The diary mentions one resident walking to market, while the photograph description includes a delivery truck. This suggests different documented transportation uses at those two times. It does not prove that nobody used vehicles anywhere in the community in 1920. Absence from one account is not proof of absence from all community life.

Worked timeline: Mark every decade between 1920 and 2020. Count three equal intervals to reach 1950 and seven more to reach 2020. Label the units and explain that the line covers a century. If investigating a shorter period, a years scale might make individual events easier to distinguish.

Guided local investigation: With teacher support, obtain an actual dated photograph, map or firsthand account from a local archive, library or family collection that may be shared. Pair it with a later source, record each source's origin and compare a specific place or activity. Use only evidence available in the sources, distinguishing observation from inference.

Independent evidence: Construct a scaled timeline, identify the roles of two sources and write a change claim supported by details from both. Include one question the sources cannot answer. Keep fictional practice records separate from actual local evidence; do not present the Mill Creek model as the history of the reader's community.