plate tectonics

Name: _____________________________________________________________________________ AST 111A Lab #8: Plate Tectonics Background: In this lab we will look at some before-and-after maps of the distributions of the continents over geological time, measure how far they have moved on the map, and calculate their actual speeds. Procedure: 1) On the last page of this lab is a sequence of maps of the world, from the time of the supercontinent Pangea to the present day. There are seven geological continents labelled, which we will number as indicated here: North America (1), South America (2), Eurasia (3), Africa (4), India (5), Australia (6), and Antarctica (7). (Note that Eurasia is a combination of Europe and Asia, which have been geologically fused since before the time of Pangea.) 2) With a pencil, draw a reference point at the approximate center of each of the seven continents of the modern map, and label each with the corresponding continent number. Do the same for the Pangea map. (You may omit the two maps of intermediate age.) 3) Since everyone’s maps will not print out the same size, we need to construct a specialized ruler to measure distances. Look near the center of the modern map. Along the edge of a sheet of paper, make two marks that span the distance along the equator between the two white vertical (longitude) lines that lie between South America and Africa. This will be our unit of distance measurement for the maps. Label this segment on the map also. 4) Repeatedly reposition the edge of the paper along this segment of the map to make a series of equally spaced marks, until the total width of your ruler is at least as great as the width of the map. Note that you cannot just mark all the segments across the equator that you see, because they are not all the same size. 5) Label the leftmost mark as “0”, the mark to the right of it as “1”, the next one as “2”, etc. Then go back and make shorter marks to subdivide the space between each pair of marks into ten equal-as- possible smaller intervals. Your ruler can now measure to the nearest tenth. 6) Use your ruler to measure, to the nearest tenth of a unit, the distance between the reference points you labelled for each pair of continents on the Pangea map. Do the same for the modern map. Record your measurements in the data table. 7) For each pair of continents, subtract their Pangea-era separation from their modern-era separation to determine the distances they have moved relative to each other. (Note that any negative numbers mean that those continents have moved closer together.) Record your results in the table. 8) Our goal is, given how far the continents have spread out from each other and the amount of time involved, to calculate their average speeds. This requires knowing a number of conversion factors, but since this class is called “Descriptive Astronomy” most of the math has been done for you. All you need to do to get the continent speeds in inches per year is to multiply your changes in distance (in your ruler units) by 0.64 . Do that calculation for each pair of continents, and record your results in the table.

9) Be sure to include with your submission an image of your map page, with the segment in the Atlantic Ocean that was used to make the ruler indicated, and the reference points marked and numbered. Data: continent pair Pangea distance modern distance difference actual speed in in ruler units in ruler units in ruler units inches per year 1 and 2 _______________ _______________ _______________ ____________ 1 and 3 _______________ _______________ _______________ ____________ 1 and 4 _______________ _______________ _______________ ____________ 1 and 5 _______________ _______________ _______________ ____________ 1 and 6 _______________ _______________ _______________ ____________ 1 and 7 _______________ _______________ _______________ ____________ 2 and 3 _______________ _______________ _______________ ____________ 2 and 4 _______________ _______________ _______________ ____________ 2 and 5 _______________ _______________ _______________ ____________ 2 and 6 _______________ _______________ _______________ ____________ 2 and 7 _______________ _______________ _______________ ____________ 3 and 4 _______________ _______________ _______________ ____________ 3 and 5 _______________ _______________ _______________ ____________ 3 and 6 _______________ _______________ _______________ ____________ 3 and 7 _______________ _______________ _______________ ____________ 4 and 5 _______________ _______________ _______________ ____________ 4 and 6 _______________ _______________ _______________ ____________ 4 and 7 _______________ _______________ _______________ ____________ 5 and 6 _______________ _______________ _______________ ____________ 5 and 7 _______________ _______________ _______________ ____________ 6 and 7 _______________ _______________ _______________ ____________