← Back to course
Earth and Space 6-8 / Week 10 / Wednesday
3/6
Week 10 · Reading the Layers

Wednesday

Sky Deck Lab: The sediment bottle
// Oldest at the bottom, youngest on top
⏱ about 20 min

Wednesday: Sky Deck Lab: The Sediment Bottle

A grown-up tightens the lid. Rocket shakes the bottle over the sink until everything is a brown swirl.

"Go!" Raven starts the timer. "Call out what lands."

"Gravel, already down," Rocket says. "Sand, sinking. Soil, still floating. The water is cloudy."

Nova hovers at eye level with the bottle. "The textbook timed single grains," she says. "A granule in less than half a second."

"And fine clay may never settle," Raven reads from her notes. "What do you notice at one minute?"

Rocket looks. "Three bands. And the top one is still growing." Nova hums. "Measure, then wait, then measure again."

Your mission

Today you make layers the way a lake or a sea does. You shake sediment into water and let it settle.

You will predict the order, time what you see, and measure each layer in millimeters after it settles.

The textbook says a granule sinks in less than half a second and a sand grain in a second or two. Silt takes several seconds, and fine clay may never reach the bottom.

  • A clear plastic bottle or jar with a lid that seals
  • A handful each of gravel, sand and soil from your own yard or a path
  • Tap water to fill the bottle about three quarters full
  • A ruler with millimeter marks, a timer or clock, and your Sky Log
  • A sink or an outdoor spot, and a towel for spills
Safety first
A grown-up tightens the lid before any shaking. Shake over a sink or outdoors.
Gravel, sand and soil come from your own yard or a path, never a park or a garden bed.
Nothing is tasted. Keep small gravel away from younger children.
Wash your hands when you finish, and wipe up spills right away.
  1. Put the gravel, sand and soil in the bottle. Add water until it is about three quarters full.
  2. Have a grown-up tighten the lid. Predict the order of the layers in your Sky Log before you shake.
  3. Shake the bottle for ten seconds over the sink. Set it down and start the timer at once.
  4. Watch and call out which sediment lands first, next and last. Note the time of each.
  5. At one minute, hold the ruler against the bottle and measure the thickness of each layer in millimeters.
  6. Wait ten more minutes without moving the bottle. Measure again and note whether the water is clearer.
  7. Leave the bottle overnight on the Sky Deck. Tomorrow, measure once more and look for a thin top layer of fine mud.
  8. Copy all three sets of measurements into your data table.
PREDICT BEFORE YOU SHAKE
  • Read the question.
  • Tap your answer.
Which sediment will land on the bottom first?
After the bottle sits overnight, where will the finest mud be?
LayerLanded at (seconds)Thickness at 1 minute (mm)Thickness at 11 minutes (mm)Thickness next day (mm)
Bottom layer
Middle layer
Top layer
Water above: clear or cloudy?

Why big grains win

The textbook explains the race. Gravity pulls a grain down in proportion to its mass. Friction with the water resists in proportion to its surface area.

For a large particle, gravity wins easily, so it drops fast. For a tiny particle, the two forces are closer, so it drifts down slowly.

Small particles that settle slowly spend longer in the water. If the water is moving, they travel farther before they land.

That is why the bottom of your bottle is gravel and the last thin film is mud. A real sea floor works the same way, only slower.

What the lab showsTrue or false?
The bottom layer in the bottle is the one that formed first.?
The finest particles settle fastest.?
The bottle shows superposition: older below, younger above.?
One shake of a bottle takes as long as a real rock layer.?
WHY THIS EXERCISEYour bottle is evidence for the rule you will use to read real cliffs.
How many kinds of sediment did you put in the bottle? Type a number.
WHY THIS EXERCISEThree sediments make three layers, and three layers are enough to show an order.
Sketch your bottle after one minute and again after it sat overnight. Label each layer and write its thickness in millimeters.

A sea floor in a bottle. Tomorrow you read a real canyon wall and the gap hidden inside it.

← Tuesday