As to why Earth is layered, early in its history
it got hot enough (from gravitational
compression, the energy of impacting bodies, and
radiation, to have partially melted. When this
happened, the densest material sank toward
Earth's center, while the less dense stuff rose
to the top. It's a little like a hot chocolate--
foam floats to the surface, and the heavy syrup
settles to the bottom.
And about dinosaurs: thousands of books and
articles have been written about this
controversial subject. One important thing to
keep in mind is that not all dinosaurs became
extinct--many thousands of species are still
very much with us. They happen to be covered
with feathers. We call them birds, of course.
Although most people don't appreciate this idea
yet, birds are as much dinosaurs, as poodles are
dogs. Birds have many unique qualities relative
to other dinosaurs, just as poodles are special
compared to other dogs, but birds are dinosaurs
and poodles are dogs just the same. So, what
killed off the dinosaurs that weren't birds?
Most scientists now agree that a catastrophic
collision with an asteroid at the end of the
Mesozoic is what did them in. Why non-bird-
dinosaurs and many other kinds of organisms,
disappeared at this time, while many other
groups survived, is what we're having a
difficult time explaining.
The major layers of the Earth, starting from
its center, are the inner core, the outer core,
the mantle, and the crust. These layers formed
as the building blocks of Earth, known as
planetesimals, collided and collapsed under
their own gravity around 4.5 billion years ago.
At that time, the heaviest elements (like iron
and nickel) sank to the core, while the lighter
elements (like silicon, oxygen, and carbon),
rose to form the mantle and crust.
The crust itself is composed of many layers,
which are the ones we can see at the surface.
Most continents have a crystalline core, known
as a 'kraton'. Every continental kraton is then
draped in many layers of sedimentary, igneous,
and metamorphic rock. The most dramatic layers,
like those in the mountain ranges above Santa
Barbara, are often sedimentary rocks, which
formed as long-gone mountain ranges eroded away
and the resulting sediments were deposited
somewhere else on the continent. A change in
tectonic plate motion then caused those
sedimentary layers to be brought up to where we
can see them today.
When volcanoes erupt, the lava that comes out
can spread across broad areas, forming a layer
of igneous rock within the sedimentary layers.
Thus, most of the layering on the Earth's
surface is due to erosion and deposition of
mountain ranges, and lava flowing out on the
Most scientists believe the Dinosaurs became
extinct at the end of the Cretaceous period
(around 65 million years ago) when a large
asteroid impacted the Earth, probably causing
global fires, giant tsunamis, and major climatic
change. In addition to Dinosaurs, nearly 75% of
all plant and animal species on Earth went
extinct around that time. This event is known
as a "mass extinction". It is possible that
more than one asteroid hit the Earth, as
scientists have found multiple large impact
craters that date to the same period.
The other leading theory for the mass
extinctions is the eruption of huge volumes of
basaltic lava in India, an event known as the
Deccan Traps. This enormous amount of lava was
erupted in a relatively short time period, and
could have drastically altered climate, changing
habitat zones faster than the plants and animals
could adjust to them.
It is likely that both the Deccan Traps and
the impact of multiple asteroids contributed to
the demise of the Dinosaurs and so many other
species at the end of the Cretaceous.
Layers of rocks are formed when sediment is
laid down, and flattens out to be as close to
the center of the Earth as possible. Then, a new
layer is laid down, which has to fall onto the
older layer, and thus lies above it.
Dinosaurs are not extinct - birds are living
dinosaurs. The cause of the extinction of the
non-bird dinosaurs is not completely known,
although there is reason to think that it had
something to do with an asteroid impact in
Mexico about 65 million years ago.
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