Lesson Plan

Stratigraphy and Superposition in Archeology

Grade Level:
Upper Elementary: Third Grade through Fifth Grade
Subject:
Science
Lesson Duration:
60 Minutes
Thinking Skills:
Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words. Analyzing: Break down a concept or idea into parts and show the relationships among the parts.

Essential Question

How do stratigraphy and superposition help archeologists date layers in archeological sites?

Objective

Students will:1) Learn about the concept of superposition and 2) Apply superposition to understand the relationship between soil strata and the relative age of archeological artifacts.

Background

This lesson plan is one in a series that uses archeology to teach concepts everyone needs to know. It can be used as-is, or be customized with images, objects, or stories representative of a particular park or place. Other lesson plans in this series are:

Preparation

Print several copies of the file "Building Cutaway" and enough copies of the file "Stratigraphic Profile" for each student.

Materials

Download Building Cutaway

Download Stratigraphic Profile

Lesson Hook/Preview

Show the class the "Building Cutaway" image or a picture of an apartment building or another structure with the front cut away.

Explain to the class that stratigraphy is a method used by archeologists and geologists (in fact, it was first developed by geologists!) to date layers (strata) of earth using the concept of superposition. Superposition is which layer is oldest, next oldest, and on. Typically, the strata get older as archeologists dig into the earth, because layers accumulate one on top of another.

Show the Building Cutaway page. Say that this image of a building illustrates the concept of superposition. Ask students which floor of the building was built first, second, third, and on to the roof. Which floor is oldest and which is newest? Point to the objects in each floor of the building. Tell students that archeologists look for artifacts in layers of soil as they build up over time.

Bonus: Tell the students to imagine that an earthquake has toppled the building. How might it affect the tidy layers in the picture? How would archeologists sort out which artifacts belonged to which floor (or layer, or strata)?

Procedure

Pass out the Stratigraphic Profile activity page for students to work in pairs. Look over it together. Reinforce their understanding of superposition by asking: Which is the oldest layer? Which is the newest layer?

Tell students that you are going to share with them the story about an archeological site close by, starting with the oldest habitation of the site. Instruct them to listen closely and draw pictures of any artifacts they hear about in the corresponding layer. Read the story below.

Let's go back in time!

Before any people arrived at this place, there was a river surrounded by land and forest. Sometimes, the river flooded its banks. When the water receded, the river had left gray silt and rocks behind. This is the subsoil, or the bottom of the archeological site. (What artifacts did archeologists find in this layer? Answer is none, because people did not live in this layer.)

Two thousand years ago, a band of Native Americans stopped for the last time at their traditional hunting spot near a river. They built fire pits from large rocks, which sometimes cracked and split into smaller pieces from the intense heat. They hunted buffalo and other large animals using stone pointed tools. They also made fishhooks and caught from the river. Some of the meat they cooked for now in ceramic pots, and some of it they smoked for later. They gathered fruits, seeds, grasses and grains, and nuts. The food was stored in deerskin bags. (What artifacts did archeologists find in this layer? Answers may include: fish hooks, bones, ceramic pieces, seeds, stone projectile points, cracked rock, etc.)

In the early 1500s, the river flooded and washed a thick layer of silt and rock over the site. (What artifacts did archeologists find in this layer? The answer should be none, because this layer represents the flood, not human habitation.)

In the 1650s, Spanish explorers made a base at the site. They set up tents and used nails to fasten pieces together. They had horses, which used metal hardware for their bridles and nails for the hooves. The explorers had guns and ammunition for hunting animals. To record their observations, the explorers used carbon pencils, which broke easily into pieces. They cooked in metal pots over an open hearth and ate from ceramic dishes or wooden plates. They wore clothes with buttons and hooks, but sometimes these fell off. (What artifacts did archeologists find in this layer? Answers may include: nails, horse bones, metal hardware, nails, gun parts, ammunition, carbon pencils, metal pot pieces, ceramic sherds, button, and hooks.)

In the 1890s, several free Black families established a town by the river. They built houses and outbuildings using wood, clay chinking, and nails. Unlike previous settlements, these families had children with them, who played with dolls and marbles, or little bits of string and metal that they fashioned into toys. (What artifact did archeologists find in this layer? Answers may include: nails, clay chinking, doll parts, marbles, metal bits.)

During the early 20th century, city officials created a park here. The park had a rides made from metal and plastic tubes, beams, chains, and hardware. Vendors sold trinkets, like keychains, jacks, and dolls. Sometimes a kid fumbled a coin when buying a souvenir and it fell to the ground. Oftentimes, people got so caught up in the fun, they didn't realize that a button or hairpin was missing until they got home. (What artifacts did archeologists find in this layer? Answers may include: construction materials, keys, keychains, jacks, dolls, coins, buttons, and hairpins.)

The grassy surface is the modern day. Here's where the archeological sites of the future are being made!

5. Review the layers with the students. Ask them which artifacts are oldest, and which are most recent.

Vocabulary

Archeology: The study of the past based on the material evidence that people left behind

Artifact: An object made or used by humans

Stratigraphy: The study of the layers of earth known as strata

Superposition: A concept used in archeology and geology to date soil layers according to their relative position to each other. In general, the oldest soil layers are on the bottom and the most recent at the top.

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Tags: archeology archaeology

Last updated: December 18, 2023