00:00
00:00
03:14
BBC Bitesize: KS3 Chemistry
How Sedimentary Rock Forms
The narrator explains how sedimentary rocks form: from sediment deposited in water through the process of weathering and erosion. He also explains the layers of sedimentary rock, which include sandstone, limestone, and conglomerates.
Sign up to access lesson features such as sample questions, standards alignment, and discussion tools to check for understanding.
Comments
Please sign in to write a comment.
Video Transcript
0:03
the second main type of rock is called sedimentary
0:07
it's made up
0:08
as its name suggests
0:09
of sediment
0:10
small pieces of other rocks
0:12
and animal remains
0:13
which have already been broken down
0:15
by a process called weathering
0:19
weathering is what happens when rocks are eroded away by the action of wind and water
0:29
over thousands even millions of years
0:32
little pieces of the Earth's crust
0:34
on a road to the way
0:35
and transported Downstream
0:43
little bits of stones grains of sand and mud
0:46
are washed away
0:50
eventually all these B settle
0:51
on the bottom of rivers
0:53
lakes
0:53
and oceans
0:54
as sediment
0:58
this sediment builds up
1:00
in horizontal layers
1:01
one on top of another
1:03
eventually
1:04
the weight of the layers gets so great it squeeze the water out of the sediment
1:09
the minerals are left behind by the water
1:12
slowly cement the particles together
1:15
this
1:15
is what turns them into rock
1:20
these layers
1:21
or beds of sedimentary rock may eventually
1:25
get pushed up again
1:26
above the sea
1:27
and if that happens
1:28
the process of weathering by wind and water
1:31
can start all over again
1:33
the rock cycle
1:34
in action
1:37
if the remains of animals or plants get trapped in the layers as they build up
1:42
they sometimes get preserved
1:44
or make an imprint in the rock
1:46
this
1:46
is how fossils are formed
1:48
depending on the type of fossil
1:50
we can tell
1:51
how old the rock actually is
1:53
sometimes marks like Footprints
1:55
left behind by a creature
1:57
can be seen as trace fossils
1:59
in sedimentary rock
2:01
these are three-toed Footprints left by dinosaurs some 250
2:06
million years ago
2:08
the dinosaurs walked in soft mud
2:10
at the edge of a lake
2:11
their Footprints
2:12
were then baked hard in the sun
2:16
then
2:17
when more sediment was washed over the footprints
2:19
they became
2:20
very slowly
2:21
locked inside their layers of sedimentary rock
2:25
now
2:25
all this time later
2:27
the layers above them have been weathered away
2:29
revealing these Footprints an
2:31
edible 250 million years
2:34
after they were made
2:38
take a closer look at some buildings
2:40
and you'll see that a different examples of sedimentary rocks
2:44
like Sandstone
2:45
Limestone
2:47
and conglomerate
2:51
Sandstone is as it sounds
2:53
made of grains of sand squeezed and cemented together
2:57
limestone
2:58
is made of the mineral called calcite
3:01
from evaporated sea beds
3:02
and ground up animal shells
3:05
conglomerate rock
3:06
is a conglomeration of larger Pebbles and grit
3:09
again cemented together
3:11
under the weight of the sediment
Paula Weaver