Sea Floor Spreading (Day 1/2)

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SWBAT create a graph modeling the process of sea-floor spreading in continental drift (and rock formation)

Big Idea

In this lesson, students construct a graphical model of the ocean floor (the Atlantic Ocean), describing its physical features, identifying its plate motion and associated characteristics, and diagraming its magnetic polarity

Lesson Introduction

[Note: For embedded comments, checks for understanding (CFUs), and key additional information on transitions and key parts of the lesson not necessarily included in the below narrative, please go to the comments in the following document: Sea Floor Spreading (Whole Lesson w/comments). Additionally, if you would like all of the resources together in a PDF document, that can be accessed as a complete resource here: Sea Floor Spreading (Entire Lesson) [PDF Version]. Finally, students may need their Earth Science Reference Tables [ESRT] for parts of the lesson (a document used widely in the New York State Earth Science Regents course) as well.]

This lesson is the first day of a two-day lesson involving the process of sea floor spreading. Since the lesson itself is pretty ambitious in terms of what students are tasked to do, it necessitates at least two periods (I have around 60 minutes/period) of task time in order for students to complete everything. The lesson itself involves a brief introduction on mid-ocean ridges as divergent plate boundaries that extend and widen the ocean basins. Students then construct a graphical profile of the elevation of the ocean floor, labeling and identifying key features. 

Do Now & Objective(s)

10 minutes

Students come in silently and complete the (attached) Do Now. After time expires (anywhere from 2-4 minutes depending on the type of Do Now and number of questions), we collectively go over the responses (usually involving a series of cold calls and/or volunteers), before I call on a student and ask them to read the objective out loud to start the lesson.

As a general note, the Do Now serves a few purposes:

  1. It serves as a general review of the previous day's material;
  2. It is a re-activation of student knowledge to get them back into "student mode" and get them thinking about science after transitioning from another content area or alternate class;
  3. as a strategy for reviewing material students have struggled with (for example, using this as a focused review for material that they have struggled with on unit assessments or recent quizzes); and,
  4. It is an efficient and established routine for entering the classroom that is repeated each day with fidelity (I never let students enter the classroom talking. While it may seem potentially severe to have students enter silently each day, this is both a school wide expectation and a key component of my classroom. In many respects, I find that students readily enjoy the focus that starting with a quiet classrooms brings each day).


Note Section

15 minutes

Students are coming in with a fairly good base on the various types of crustal movement and plate boundaries, but this lesson focuses in specifically on the divergent boundaries at mid-ocean ridges. We start the lesson with a brief introduction pulled from an Earth Science textbook. I wanted to embed specific CFUs that I could both ensure that students complete successfully for comprehension, so I put those directly into the resource.

While the questions themselves are fairly straightforward, they give students an opportunity to work together (I have them do this assignment with their table partner) and ensure clarity and consistency of answers. I then, before we go into the graph portion of the lesson, randomly (using my popsicle sticks) cold call on students to read their responses out loud. I then have students add or modify their responses as necessary based upon what students say (after one student is cold-called, I usually ask 1-2 other students to agree, elaborate on, or add to the original student's response). 


25 minutes

The actual graph, the main part of the lesson, due to its complexity and the multifarious ways in which students create, manipulate, and analyze the information, is the part of the lesson that is spread over two days (see next day's lesson here).

Attached in the graphing resource, there are two pages. The first page contains information that they'll actually graph out to create a sea floor profile. It contains information on both the depth (in kilometers below sea level) and the distance from the east coast of the North American shoreline. 

As they start, students should first be tasked with the usual graphing steps - identifying the variables and determining the appropriate scale and intervals to use. I take some whole-group time to make sure that they get the chance to think through what goes where. The x-axis has been labeled for them, but they need to think constructively about how to structure the intervals on both axes in order to make sure it takes up most of the space on the graph. Additionally, since this is an actual profile of the ocean floor, most of the values on the y-axis (the depth) are going to be negative. Ultimately, only a small portion of the values should actually be positive. Most of the y-axis space should extend into negative values - the lowest point on the profile is -5.0 km so the y-axis should extend at least that far down. 

Quite frankly, I find that the discussion and plotting of the axes and intervals on the graph takes the remainder of the class period. Some really advanced students may be at a point where they can start graphing, but by extending the class into multiple days, students get the opportunity to graph at their own pace, and then do a legitimate analysis of much of the data. I didn't find it too hard for students to pick up where they left off, either. Most everyone was able to jump back in without too much trouble (Note: Again, please note tomorrow's lesson as indicated here). 


5 minutes

Unlike most of my other lessons, there is no summative assessment at the end. Due to the multi-day nature of the graphing exercise, the closing consists of packing up and, if necessary, collecting any materials or resources to make for efficient distribution the next day (personally, I ask my students to hold onto the information for the next day, but if it suits your classroom or is more efficient from a logistical perspective, it might be easier to collect the information and hold onto it).