Plate Tectonics: Age Is But A Number… Until It’s Evidence


When I moved from middle school science to high school science, one of the most surprising things I encountered was how much my high school students enjoyed coloring. Now obviously, science is more than an art project.  [And along those lines, as Steven L. Pruitt mentioned, “If you can eat it, it’s probably not a model.”]

A post shared by Mrs. Sadler (@sadlerscience) on

That said, when I was trying to figure out a way for students to explore the age of Earth’s crustal rocks during my unit on Earth’s geologic history, coloring wasn’t too bad of an idea.  

The intention of the standard is for students to evaluate and use evidence, as well as the theory of plate tectonics, to explain patterns (hello, Crosscutting Concept!) in the ages of Earth’s crustal rocks.  Well, before they could really get into looking at any sort of evidence or even the theory of plate tectonics, I wanted students to see the patterns they were going to be explaining.  

Exploring Age of Crustal Rocks

plate tectonics age of rocksI figured I had two options — I could simply present my students with a map, color-coded to identify the ages of oceanic crust, or I could somehow engage them in an activity where they discover those ages themselves.  The first option seemed kind of boring (although that’s not to say I don’t use data with my students! It’s definitely one of my go-to Science and Engineering Practices!). Even so, I wanted to do more than just give my students a map, so I decided on the second option.  That said, I quickly realized it would be very time consuming for students to plot the age of Earth’s crustal rocks on a large enough scale to complete a global map.  While that, admittedly, would have been perhaps a better representation of collecting data, it just wasn’t feasible in my classes with my curricular requirements.  Instead, I put together a simplified version where I provided the outline and a “color by number” approach to “collect” the relevant data.

Students colored their maps, following the key provided, and then they analyzed their maps to first identify patterns and then make sense of the patterns they found.  Because I had marked the location of mid-ocean ridges, and they could obviously see where the continents sat, they were able to connect the formation of new rocks at the ridges and the disappearance of “old” rocks where ocean crust met the continents.  Eventually, students discovered these “old” rocks were recycled back into the crust by subduction at the ocean-continent convergent boundaries, but at this point in the game, we were just focusing on patterns in the age of the crust.

After maps were finished, we debriefed together during the first part of our Explain phase.  We used the “What I See, What It Means” analysis method to identify patterns we saw and interpret those to figure out what they meant.  Through the discussion, students concluded:

  • new rocks are formed by mid-ocean ridges
  • the rocks get older as they move away from the ridge, indicating the crust is moving (hey, plate tectonic theory!)
  • the oldest rocks could be found near the edges of the continents


We were on our way to meeting our standard!  If this is an activity your students might enjoy, you can find it in my TeachersPayTeachers store.  It’s also available to Silver, Gold, and Platinum members of the Science Teacher Tribe in our exclusive NGSS Resource Library.

Science Teacher Tribe: Convenient and Comprehensive NGSS Professional Development

If you are anything like me, transitioning to the NGSS can be totally overwhelming.  Teaching is hard as it is – you’re busy keeping up with the “normal” lessons day to day and week to week, plus grading, meetings, IEPs, behavior management, so on and so forth. I get it. Who has the time or energy to figure out all that goes into these new standards and their impact on your curriculum, let alone what it means for your teaching!

Well, I’m happy to say there IS an easier way. You don’t HAVE to muddle through everything, and you definitely don’t have to do it alone!

Imagine feeling confident that the curriculum you designed is actually aligned to the standards, that your units incorporate the three dimensions and engage your students in Science and Engineering Practices that matter. Imagine classes full of students who take ownership of their learning, who thrive on “figuring it out” and “puzzling through it” and come to learn the content through discovery.  Imagine days where you DON’T have to stand in front of the class, battling for their attention, delivering boring lectures and notes, printing worksheet after worksheet, and wasting tons of time on review and reteaching — only to have your students fail to perform anyway. Imagine learning that sticks, and engaging activities (that you may already be doing!) but that lead to true understanding.  It’s not magic, and it doesn’t necessarily come easy, but it IS possible.  

Learn more at the Science Teacher Tribe Course and Community.