The Ocean Floor

Activities to try

1. 1

   Tap across a to-scale seafloor profile

   Why it works: The ocean floor has varied terrain — mountains, ridges, plains and deep trenches — not a uniform flat sandy bottom, and these resemble landforms found on land.

   1. Before seeing the profile, predict aloud what the bare seabed would look like if all the water drained away — flat and smooth, or varied? Then study a wide to-scale cross-section running from the shore outward across an ocean basin: continental shelf → slope → abyssal plain with seamounts → mid-ocean ridge → abyssal plain → a deep trench near the far edge, beside an island arc.
   2. Tap or point to each feature in turn (ridge, seamount, abyssal plain, trench) and say its name and one fact about it.
   3. Check your earlier prediction against the profile: is the bare seabed flat and smooth, or varied? Say what surprised you.
   4. Compare each undersea feature to a land feature it resembles (undersea mountain range, deep valley) and state that the seafloor has similar kinds of features to dry land, just hidden underwater.
2. 2

   Drop Everest into the trench

   Why it works: Challenger Deep in the Mariana Trench (~10,935 m) is deeper than Mount Everest (8,848 m) is tall, so Everest would still sit about 2 km underwater — a memorable way to grasp how deep the ocean's deepest point is.

   1. Look at a vertical depth ruler marked in metres, with the sunlit surface zone at top and Challenger Deep at the bottom.
   2. Place (or trigger a 'drop Everest in' control that places) Mount Everest upright, with its base on the floor of Challenger Deep in the Mariana Trench, beside the ruler.
   3. Read where Everest's summit stops and state that it is still roughly 2 km below the surface — the mountain is fully drowned.
   4. Answer: which is greater, Everest's height (8,848 m) or the trench's depth (~10,935 m)? Then say the deepest point of the ocean is deeper than the highest mountain is tall.
   5. Name the Mariana Trench (Challenger Deep) as the deepest point on Earth.
3. 3

   Fly or dive to the deepest point (enrichment)

   Why it works: Seafloor terrain is genuinely three-dimensional; travelling over ridges and down into the trench can convey relief and the depth of the descent, reinforcing the varied-terrain and scale ideas.

   1. Travel along the seafloor in a flythrough or a descending submersible: skim an underwater mountain range, cross the flat abyssal plain, then plunge into the Mariana Trench.
   2. Watch a live depth readout and call out when it passes 8,848 m — the 'Everest height' milestone — on the way down to ~10,935 m at the trench floor.
   3. Describe aloud how the relief and depth change along the journey, and how far past the Everest milestone the descent continues.