Cycles on Earth
Section: Earth and Space | Syllabus: Cambridge Primary Science (0846)
The Rock Cycle
- Rocks are constantly being recycled over millions of years
- the rock cycle describes how rocks change from one type to another
Key Processes
| Process | What Happens |
|---|---|
| Weathering | Rocks are broken into smaller pieces by rain, ice, wind, or plant roots |
| Erosion | Broken pieces are carried away by water, wind, or ice |
| Sedimentation | Sediments settle in layers (e.g. at the bottom of a lake or sea) |
| Burial | More layers build up on top, pressing down on lower layers |
| Metamorphism | Heat and pressure deep underground change rocks into metamorphic rocks |
| Melting | Rocks melt deep underground to form magma |
| Solidification | Magma or lava cools and hardens to form igneous rock |
Fossil Formation and Rock Age
How a Fossil Forms
- Step 1: the animal dies
- Step 2: it is quickly buried by sand and clay
- Step 3: the soft tissues decompose, leaving the hard bones
- Step 4: more sand and clay build up on top and harden into rock
- Step 5: the bones are gradually replaced by minerals
- Step 6: erosion of the rock years later reveals the fossil
The Deeper the Rock, the Older It Is
- Rock layers build up over time, with new layers forming on top of older ones
- this means the deeper a rock layer is below the surface, the older it is
- fossils found in deeper rock layers are therefore older than fossils found in shallower layers closer to the surface
Worked Example: October 2024 Paper 1
Question: the rock cycle describes the formation of different types of rock.
Look at part of the rock cycle.
Complete the sentences. Choose words from the list.
erosion fossils heat melting pressure
sedimentation solidification
Sedimentary rock changes to metamorphic rock because of heat and
......................
The metamorphic rock is broken into small pieces and transported by
......................
The small pieces of rock are deposited in a lake and form new sedimentary rock by
......................
[2 marks]
Answer:
Pressure
Erosion
Sedimentation
Phases of the Moon
- The Moon does not produce its own light - it reflects light from the Sun
- as the Moon orbits Earth, we see different amounts of the sunlit side, which creates the phases of the Moon
The Monthly Cycle (approximately 28 days)
| Phase | What We See |
|---|---|
| New Moon | Moon is between Earth and Sun - we see the dark side (no light visible) |
| Waxing Crescent | A small sliver of light appears on the RIGHT side (getting bigger) |
| First Quarter | Right HALF of the Moon is lit |
| Waxing Gibbous | More than half is lit, still getting bigger |
| Full Moon | Earth is between Moon and Sun - we see the whole lit face |
| Waning Gibbous | More than half is lit, getting smaller |
| Last Quarter | Left HALF of the Moon is lit |
| Waning Crescent | A small sliver of light on the LEFT side (getting smaller) |
- Waxing: getting bigger - more of the Moon is lit each night
- Waning: getting smaller - less of the Moon is lit each night
Worked Example: Spotting an Anomalous Result
- Question: pictures of the Moon are put in order from new moon to full moon and back to new moon again. One picture does not fit the pattern. How can you tell?
- Answer: from new moon to full moon, the lit part should keep increasing in size, and from full moon back to new moon, it should keep decreasing. A picture that shows more or less light than expected for its position in the sequence is the anomalous result
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