Identifying Types of Plate Boundaries

Based on the story, and on the Map of Griphus, identify the location of any of the following types of plate tectonic boundaries that are clearly present: 1) continent-continent convergence, 2) continent-ocean convergence with subduction, 3) ocean-ocean divergence, 4) continent-continent divergence. Cite the evidence seen on the map for each that makes you sure that it is present.

The plate tectonic origin of the mountains in Pugnus are less clear from the map than the mountains in Manus or the mid-ocean range. That is, they aren't obviously associated with a divergent or convergent boundary. In terms of plate tectonic processes, and the passage of time, how might they have formed?

Ocean Crust Ages

Based on the story, draw a pattern of ages for the ocean crust between Manus and Pugnus. Include both the pattern of ages and the value of the ages of the rock.

Inferring the Past

Based on the story, and on your understanding of plate tectonics, identify on the Map of Griphus where the third artifact is most likely located. What is your reasoning?

How is this relationship similar to the evidence for continental drift cited by Alfred Wegner in 1912 (such as the location of the fossil for a small land reptile, the mesosaur)?

Radioactive Half-life--A Puzzle of Time

The Wormers—and now our heroes—used Berkelium for power. The isotope of Berkelium that appears in the story is one that has never been manufactured on Earth (Berkelium is not a naturally-occurring element on Earth). It's unlikely that such an isotope occurs naturally, even on another planet. However, it's an interesting math exercise, and an interesting exercise in understanding the idea of half-life, to consider why this isotope must be one that hasn't been manufactured on Earth.

The longest half-life for any known isotope of Berkelium is about 1380 years. The planet Griphus must be at least 30 million years old to fit with the story (and would reasonably be much older).

How many half-lives pass in 30 million years? (30 million divided by 1380)

Suppose that Griphus started out as pure Berkelium (an absurd conjecture...but let's suppose). Perhaps about 6 x 10⁴⁹ atoms of Berkelium.

That's 60 thousand billion billion billion billion billions. Quite a lot.

How many would be left after 1380 years? (half, or 3 x 10⁴⁹ atoms of Berkelium)

How many after 2 x 1380 years = 2760 years?

How many would be left after 207000 years (150 half-lives)

150 half-lives corresponds to 150 halvings. Or 0.5¹⁵⁰ = 7x10^-46.

On average, there would be only about 40000 atoms left.

How many in another 1380 years? (half, or 20000 atoms)

How many would be left after 227700 years (165 half-lives)?

165 half-lives corresponds to 165 halvings. Or 0.5¹⁶⁵ = 2.1 x10^-50.

On average, there would only be a single atom of Berkelium left after only 227,700 years. And the planet has at least 29,772,300 years to go.

Here's a puzzle for you. How long would the half-life of the Berkelium isotope need to be in order to have a reasonably large deposit left after 30 million years?

Other Plate Tectonic Activities

You can check out more plate tectonic activities in the Teacher Resources for the story Plate Tectonics and Non-Platonic Relationships by Alicia Cole at Teacher's Resources for Plate Tectonics and Non-Platonic Relationships.

~~———————————————————————————~~

The Teacher Resources for Jigsaw are written by Russ and Mary Colson.

Return to

Jigsaw by Douglas Smith

Return to “Eww, There’s Some Geology in My Fiction.”

Find more essays, games, and stories at

Issues in Earth Science.