Weathering breaks rocks into fragments, which are
transported to the ocean by rivers. The fragments
fall to the bottom of the ocean as sediments.
The sediment particles become
squashed (compaction) and are
cemented together by mineral.
After a very long time,
sedimentary rock is formed.
Sedimentary rock changes into
metamorphic rock when it comes
under heat and pressure. This
happens because it gets buried
deep underground and comes
close to hot molten rock.
The particles in chalk and
limestone are rearranged to form
marble.
Fossils form in
sedimentary rock
when:
Organisms fall
into sediment.
There is not enough oxygen to cause the organism to decay.
The organism has
hard enough parts to
leave a caste in the
forming rock.
Water filtering through
the rock deposits
minerals in the caste.
Chalk is full of
microscopic fossils
because of the sediment
from which it is made
comes from the shells of
microscopic sea
organisms.