Introduction to plate tectonics · 7jbwX1Uvd18 · 4:35
Sketchnote in the works
status page/video ID saved · analysis package pending
Unit 11 · Earth Science arc · 7th grade
Solid,
not still.
The ground under your chair is moving right now — slower than your fingernails grow, and unstoppably. Continents drift, oceans open, mountains rise. One small freshwater reptile left the proof on two different coasts.
a cracked shell
6 manipulatives
12 flashcards
1 reptile
it couldn't swim salt water. so where was the ocean?
The phenomenon · scrub 270 million years
The Reptile That Couldn't Swim an Ocean
Mesosaurus: a small freshwater reptile, 270 million years dead. Its fossils turn up in exactly two places — eastern South America and southern Africa. Freshwater animals don't cross salt oceans, and it had no wings. So either it broke the rules… or the ocean wasn't there. Scrub the years and watch the Atlantic open.
270 Ma · joinedtoday · 3,000 km apart
Alfred Wegener read the map like this in 1912 and said the unsayable: the continents move. The fossils agreed. The rocks agreed. The coastlines agreed. Geologists said he was a crank — until WWII submarines mapped the seafloor and found the smoking gun lying in the middle of the ocean. The data was right before the theory was allowed.
Watch · Khan Academy
The theory, and the smoking gun
The case file · four independent witnesses
The evidence never met itself
Four separate lines of proof, gathered by different people with different tools over a century — all pointing the same direction. That's how you know it's not a coincidence.
01
Fossil twins
Mesosaurus in Brazil AND South Africa. Cynognathus and Lystrosaurus on three continents each. Identical land animals, separated by salt water — unless there was no water between them.
02
Matching rocks
The same rock layers, same ages, same mountain belts line up across the Atlantic — Brazil to Ghana, Appalachians to Scotland. The mountains were one range, split mid-slope.
03
The jigsaw coastlines
Everyone notices it on their first globe: South America's bulge fits Africa's bite. Wegener's starting point — and still the class favorite.
04
The smoking gun
Seafloor mapping after WWII: the youngest rock sits at the mid-ocean ridge, getting older symmetrically away from it. The ocean floor is being made at the middle and spread outward.
Manipulative · the conveyor
The shell is cracked — and it rides
Earth's rigid outer shell — the lithosphere — is broken into about 15 major plates, floating on a softer, slowly-flowing mantle (the asthenosphere). Heat from the core rises, cools, sinks: convection, the planet's conveyor belt. Watch it turn.
the conveyor never stops — it just moves at fingernail speed
Fingernail speed
Your fingernails grow about 3.5 cm a year. The Atlantic widens about 2.5 cm a year. Continents move at literally fingernail speed — and given a hundred million years, that's an ocean.
Scale check
Plate tectonics is the champion of Scale, Proportion, and Quantity: centimeters per year × millions of years = oceans opening, mountains rising, and a map that never sits still.
Manipulative · three moves
Where the action is: the edges
Plates barely change in the middle — everything interesting happens at the boundaries. Apart, together, or sideways: pick a move and run it.
divergent: the blocks drift apart and new crust wells up between them — Iceland is splitting down the middle this way (you can SCUBA in the crack).
Standards: MS-ESS2-2 — geoscience processes change Earth's surface at varying time and spatial scales · MS-ESS2-3 — fossil, rock, coastline, and seafloor evidence of past plate motions (NGSS Lead States, 2013). DCIs: ESS2.A Earth's Materials and Systems, ESS2.B Plate Tectonics and Large-Scale System Interactions. CCCs: Scale, Proportion, and Quantity (fingernail speed × deep time), Patterns (the evidence agrees).
Myth-busters · tap to flip
Unlearn these three things
Manipulative · Spaced repetition
Say it like a scientist
Twelve words. Flip the card, grade yourself honestly, and the deck schedules your next review — hard words come back sooner. Come back tomorrow and it remembers you. (It lives in your browser, no account.)
–due now
–locked in
–seen so far
flip the card, then grade yourself
Sketch · sketchnotes
Map the plates before you explain the drift
The exact page videos are identified. Printable sheets stay pending until transcript and analysis packages pass the sketchnote source gate.
Plate tectonics and the ocean floor · A98wPKiPMJw · 4:00
Sketchnote in the works
status page/video ID saved · analysis package pending
Investigate · evidence first
Make the boundary move
The plate and seafloor models remain usable now; a print-first prediction record is queued after source review.
Investigation in the works
Use the existing page models now. The exact transcript package and classroom record are still pending.
in the worksExit ticket · 5 questions
Before you leave the ridge
No grade, no stakes — just proof the drift stuck. Answer all five to earn the stamp.
question 1 of 5