How Are Sedimentary Rocks Formed

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Transcript How Are Sedimentary Rocks Formed

When mountains are first formed, they are tall and
jagged like the Rocky Mountains on the west coast
of North America.
Over time (millions of years) mountains become old
mountains like the Appalachian Mountains on the
east coast of Canada and the United States.
When mountains are old, they are rounded and
much lower.
What happens in the meantime is that lots of rock
gets worn away due to erosion. Rain, freeze/thaw
cycle, wind and running water cause the big
mountains to crumble a little bit at a time.
Eventually most of the broken bits
of the rock end up in the streams
& rivers that flow down from the
These little bits of rock & sand
are called sediments.
When the water slows down
enough, these sediments settle to
the bottom of the lake or oceans
they run into.
Over many years, layers of
different rock bits settle at the
bottom of lakes and oceans.
Think of each layer as a page in a book. One
piece of paper is not heavy. But a stack of
telephone books is very heavy & would squish
anything that was underneath. Over time the
layers of sand and mud at the bottom of lakes
& oceans turned into rocks.
These are called
sedimentary rocks.
You may have a difficult time imagining something
solid like rocks wearing down over time - but
everything does. If you take a look in the lint trap
of your dryer, you will see that your clothes are
being worn away as they tumble in the dryer. In
fact if there is enough lint - you will see how these
bits have been laid down into layers - just like
sediments at the bottom of the lake. You will see
layers of different colors because the clothes you
dried were different - just like you will see
different layers of rocks in sedimentary rocks.
What is even more interesting is that if you
scrunch up the lint a bit like in the picture here,
you can see the layers of lint bending - just like
the layers of rock are bent. Look carefully at the
rocks in road cuts and you sill see layers of rocks
that have been folded just like the lint in your
dryer. Neat eh?!