These are fossils, they're skeletons and shells and hard parts of animals
that lived millions of years ago and they're preserved
in solid rock. But how exactly does that happen?
First to understand that, we need to understand what a fossil is
and a fossil is simply a mold or cast of the hard parts of
an animal, if you haven't watched my first video where I talk about igneous rocks
it's probably a good idea to watch that now. If you remember from the rock cycle
there are three types rocks; sedimentary and metamorphic and igneous
and fossils can only form in sedimentary rocks.
fossils like these ones are from organisms that are millions of years old
and when they died they probably were preserved something that's a lot more
like mud than rock
overtime that mud can turn into a
hard solid piece of sedimentary rock, but how does that happened?
the oldest structure that humans have built is only about 11,000 years old
and it's in ruins, but yet these fossils
show almost completely, what the body structure of the animals were
that's because in geologic time, there's enough slow time
to produce a hard solid fossil like this one.
Sedimentary rocks unlock the key to the past because they preserve information
about exactly what organisms were there, the environment
and all sorts of information about how the rocks were formed.
Sedimentary rocks are those that have formed through deposition
and solidification of sediment.
And sediment is created by weathering and erosion
it's these processes the drive the formation of new rocks in the rock cycle.
The first step in the formation of sedimentary rocks
is the breaking down of other rocks; igneous metamorphic or sedimentary rocks themselves
you take an indurated rock like this, a nice and hard rock
and you break down into small part particles
through processes of weathering. Now you can have two kinds weathering
that is mechanical weathering and chemical weathering.
Mechanical weathering has no chemical component, so it's the physical breaking down of a rock.
So that could be a rock fall, it could be
frost/ice getting in between the cracks of a rock breaking up
or salt weathering. Chemical whether on the other hand is the breaking up bonds
through medium of water. So water gets into the surface of the rock and
chemically interacts with the crystal lattice in the minerals.
Once sediments are created, you can have two different processes happen
the sediments can simply be transported by a waterway
into the ocean, where they will settle out to form new rocks
or they can create soil, and soil is simply the addition of
organic matter to that mineral component, that was formed during the weathering process.
So you see here there's lots of roots and things hanging out of this piece of soil.
If you want to learn more about soil, my friend made an amazing video
about soil that goes into way more detail
and soil is really important because it's the basis for all plant life
and we depend on agriculture which
is growing food in soil. So I'll link the video here. Once sediments have been created
and transported out in the ocean
that's where they have the chance to settle out and form new rock
sediment can be transported in many different ways; by water like
rivers, lakes, and oceans, by ice such as glaciers
and by wind, think sand dunes.
If you live in a place that gets summertime thunderstorms
you may have seen how the intense rainfall can cause runoff and erosion.
This runoff can carry sentiments into larger bodies water like rivers
and eventually those rivers will reach the ocean one way or another
if you haven't seen it in person,
it's pretty easy to do at home. Just take a jar and add some sand to it,
fill the jar of water. If you stir up the jar
you can see how the sediment will be suspended, because in energy level
of the water is higher
but if you stop stirring, given enough time those sediments will settle out
This is exactly how sedimentary rocks begin to form.
sediment is carried in water bodies until the energy level is low enough that
they begin to settle out.
this can be seen in satellite imagery
In this picture on the right the Ohio river has a higher
energy level and carries more sediment. But on the left,
the Mississippi River is at a lower energy state and carries less sediment.
Eventually the Mississippi River will reach the ocean
where it disperses its energy and all the sediment falls out
and goes to the bottom of the ocean.
the settlement eventually settles out on the bottom the ocean
and begins to compact because of all the pressure of the water above it
given time, geologic time... That is millions years
that compaction will turn into cementation
and new rock will form. Weathering, and erosion,
sedimentation and compaction and new rock formation
is what drives this part of the rock cycle.
Sedimentary rocks provide us with so much information, from what
life used to be like on this planet, to what the conditions were like
when the rock formed.
By studying and understanding sedentary rocks, geologists were able to discover
that sedimentary rocks actually exist on Mars as well.
That means that water flowed over the surface of Mars, and perhaps at one time
Mars wasn't that different from planet Earth.
In this video we learned about fossils, and
how they are formed. The definition of sedimentary rocks
what weathering and erosion is, and about sedimentation and deposition
if you have any questions about sedimentary rocks
feel free to ask them in the comments below, thanks for watching!
and stay curious about the natural world!