welcome back to earth science chapter 3 from the textbook the good earth
we're now talking about near-earth
objects and on your screen you see a
picture of an old video game from the
late seventies and early eighties called
asteroids and which a rocket ship had to
shoot lasers to break up these larger
asteroids who protect the Earth now is
that it means by which we might be able
to protect the Earth from near-earth
objects send out a spaceship to blow up
the asteroid before they hit us
well it certainly is a possibility in
chapter 3 from the good earth we're
going to talk about the characteristics
of near-earth objects and that does
include asteroids and meteorites and
yours
we're also going to talk about the
different types of impact features that
you can find the impact hazards that
exist and of course the end of the book
is basically the end of the chapter is
essentially going to give us the wanting
to beware of flying rocks back in 1992 a
football-sized meteorite crashed through
the trunk of michelle maps chevrolet
malibu classic and Peekskill New York
that meteorite was at one time a
meat-eor when it was moving through our
atmosphere and glowing brightly and
before that it was up an asteroid and
moving through space an asteroid
probably knocked out of its orbit from
the asteroid belt asteroids meteors that
become meteorites and comets as well are
all known as near-earth objects or any
oohs and they are all those asteroids or
comets that approach earth so what are
the chances that a large space object
will crash into Earth in the near future
well of course that is the question so
the earth and the moon and other
terrestrial planets all carry the scars
of past impacts with asteroids and
comets as a matter of fact this photo
from behringer meteor crater in Arizona
it's from about 50,000 years ago in a 50
meter in diameter meteorite crashed into
Earth so an asteroid that passes into
Earth's atmosphere is then considered a
media or as it's burning up in Earth's
atmosphere if it actually makes it to
the ground and strikes the ground and
then it's considered
media right now 65 million years ago it
is hypothesized that a 10 kilometer wide
asteroid struck the earth and caused the
global extinction event that took out
the dinosaurs so it's a pretty darn big
crater here in Arizona from a 50 meteor
in diameter meteorite imagine a 10
kilometer in diameter meteorite that's
what is hypothesized hit the earth about
65 and a half million years ago
have we had any near misses from eneos
well most near-earth objects Neos do not
come close enough to earth to be a real
concern but occasionally one may
approach within the moon's orbit and
that's a pretty darn big deal so there's
a lot of information on the slide this
first illustration that we see shows the
earth and the moon gives us a scale
about 50,000 kilometers and shows us the
number of eneos that have have come
quite close to Earth's orbit and then we
can see that red print just below that
illustration the green arrow points to
wear an asteroid in 2029 is expected to
fly by within thirty-six thousand
kilometres of birth and that's that's
pretty darn close and there's been other
famous flybys of eneos and you can see
those again we can see the one that's
expected to come through in april of a
2029 when they came through in 2013
it's quite small but it was really darn
close much bigger ones expected to come
through and 2028 now that's something
that will also be able to see quite
clearly in the sky so yeah there's
there's been plenty of near misses from
near-earth objects so maybe this is
something you've not really hurt anybody
talking about before and that's because
our understanding of near-earth objects
objects really dramatically increased in
the 90 so this picture on the left is
the inner solar system a chart made back
in nineteen hundred in which very few
asteroids were recognized in the inner
solar systems that's about a hundred
years ago then in the eighties and
nineties we began to look at near-earth
objects with a little bit more vigor and
then in 1999 this new chart was drawn
with more than 90,000 asteroids that
have been identified and all those
little red ones are ones that we
consider to be near Earth objects yeah
they've always been out there but we
really know much more about them now
than we did 20 50 certainly a hundred
years ago so asteroids and comets well
asteroids originated in the asteroid
belt were also they come from right now
the asteroid belt is a collection
against collection there's a lot of them
out there of cosmic debris that's
orbiting between Mars and Jupiter and
this cosmic debris is essentially debris
that was thought to have been left over
after the formation of the solar system
remember the planets become planets
because they sweep out their
neighborhoods of cosmic debris big
enough to be have their gravitational
pull create round objects but in the
asteroid belt between Mars and between
Jupiter and there just wasn't a planet
circling that could sweep out that
particular section so we got the
asteroid belt now gravitational
attraction of Jupiter pulls asteroids
out of orbit causing collisions with
other asteroids sending those or other
debris toward the inner planets so
essentially everything is in balance
until Jupiter decides to grab one of
these asteroids you can see series which
is a big one that we looked at very
closely and they pull an asteroid out of
orbit it smacks into some others some
debris flies out other asteroids fly out
and that those are the asteroids that
move toward the inner planets let's talk
about some of the characteristics of
asteroids their size anywhere from a
pebble to the size of series which is
about 940 kilometres across as they
travel at sixteen kilometers per second
or 36,000 miles per hour and generally
asteroids are composed of rock and or
metals so you have some asteroids that
are just all rock and they're called
stony meteorites when they come crashing
down to earth and then other asteroids
that have a combination of raw
rock and metals mostly iron and nickel
so let's go ahead and define again and
asteroids flying through space when an
asteroid comes into contact with our
atmosphere and enters our atmosphere
it's now media or so meteors what you
see
zipping through space briefly if you
happen to catch one a meteorite is when
that asteroid burns through the
atmosphere but strikes the Earth's
surface so about ninety percent of all
meteorite strike the earth surface are
stony meteorites and they are made up of
rocks that are very similar to the
Earth's crust
now some of those that strike the earth
have a combination of iron or a
combination of iron and nickel somehow
stone and iron some have stone iron and
nickel about all of these materials are
the materials that make up the
terrestrial planets so scientists have
popped the size and asteroids are the
leftovers from planet formation and more
than four billion years ago and have
essentially been marooned in the
asteroid belt comets are different
creatures altogether generally comments
are going to be larger than asteroids
often times many hundreds of kilometres
across
they travel faster than asteroids 50
kilometres per second or about 112,000
miles per hour and they are left over
from the cosmic debris that was part of
the formation of the solar system so
mostly they are dust with with ice and a
rocky core at one time we considered
comments to be these dirty ice balls
we've got their big huge chunks of ice
that had a lot of dirt and dust around
them but now we know that they're
actually rocky core with some ice and
then a whole lot of dust so probably
better to call them icy dirtballs some
scientists of course hypothesize that
during the heavy bombardment period
within the first two billion years of
the earth existed when there's still a
lot of debris flying around the solar
system before the planets that swept up
all that debris that comments very
likely brought ice and other critical
compounds to the early Earth the common
compound that you can find in comets
include cyanide and
carbon dioxide and water and again we
mentioned that scientists are
investigating if comets could have
supplied water in the early Earth's
oceans how do we know this about these
compounds associated with comets well
back in july of 2005 the NASA launch
spacecraft called deep impact and deep
impact launched a smaller spacecraft
called impactor that actually struck
temple 1 which is a common that circles
the the Sun every five or six years so
it's pretty amazing able to do this but
the explosion from that impact allowed
scientists to study the composition of
comets there are two types of comets we
have short period and long-period comets
and pretty interesting this illustration
shows what's known as the Oort cloud and
so the Oort cloud is this this cloud of
cosmic debris that essentially surrounds
our solar system so we talk about the
heliosphere the the region of space that
the Sun is the the biggest feature of
that would be this Oort cloud now within
the Oort cloud is the Kuiper belt that
is the belt in which some of the
comments come from other the long-range
comments come happens or cloud so short
be a short-period comets they have time
intervals of 200 years or lastly get
around the Sun and back to where they
started in 200 years or less and they
originated in the Kuiper belt and the
Kuiper belt is beyond Neptune and well
past Pluto that Kuiper belt is a belt of
a debris that circles the Sun just
outside of what we call our solar system
these types of comments are called
trans-neptunian objects and they circle
the Sun in the same direction and a
similar trajectory at the outer planets
and they returned to the inner solar
system every few years so our
short-period comets come from the Kuiper
belt and again they're basically left
over cosmic debris from the beginning of
the formation of the solar system
long-period comets they originated from
the outer limits of the heliosphere out
in the Oort cloud
and they are disrupted from the Oort
cloud by the gravitational pull of
passing stars or nebula so we're talking
about just fantastic distances here and
they tend to return to the inner solar
system over a period of decades
thousands of years and very irregular
elliptical orbits in those eligible look
elliptical orbits cross the plane of the
ecliptic at a fairly high angle in much
in the same way that Pluto crosses the
plane of the ecliptic had a high angle
the plane of the ecliptic is that plane
of the Earth's orbit and really most of
the other planets the other eight other
planets where the terrestrial Joe B&R
somewhere within a few degrees of the
plane of the ecliptic and Pluto's way
out weigh much higher angle on the plane
of the ecliptic so again these longer
period comets tend to come from the Oort
cloud they do company or $TIME o'clock
way out there the outer limits of the
heliosphere and here's a nice fairly
simple illustration of the two types of
comments with the long-period comets
coming in from the Oort cloud so that on
the left that little red line that's
just a partial path of that comet
because it's coming in from weiwei on
deep space whereas the short-period
comets they're coming in from the Kuiper
belt which is just out beyond Neptune
and Pluto and the short-period comets
orbits the Sun with similar paths of the
outer planets and then the long-period
comets have those weilong elliptical
type of orbits that cross the plane of
the ecliptic not only asteroid strike
the earth comments can as well in 1908
an explosion of a comment in the
atmosphere so it didn't strike there
that actually exploded above the Earth's
surface out in Russia destroyed forest
area the size of the major city to 2,100
square kilometers it was massive and we
have pictures the trees knocked down by
the common exploding in the atmosphere
over Russia again collisions with near
our earth objects can get the
catastrophic and can create global
extinction events so this was not really
as bad as it could have been impact
features that remain over geologic time
from the collision of
near-earth objects with earth are called
impact craters and there's essentially
two types of impact crater when an e
ennio collides with a rocky planet or
the moon's they form one of either two
types of impact craters a simple creator
or complex creator this crater and the
left from Barringer crater in Arizona
which is some meteor is a simple crater
formed about 50,000 years ago and this
was the first meteorite crater
recognized on earth and that was about
1200 meters across
so all impact craters have lots of
broken rock around them is called
brescia broken up pieces of rock nuns
pressure fractures at the base of the
crater all impact craters have this
ejected or pieces of rock and debris and
dust that are thrown from the crater all
impact craters melt the rocks in direct
contact with the actual creator and
because of a high heat and pressure all
impact craters alter minerals heat and
pressure can alter the composition of
minerals simple craters tend to simply
be bowl-shaped and they may be a few
kilometres wide complex craters are
typically more than four kilometers in
diameter and they have a central peak in
the middle where the earth is literally
rebounded from the from the collision
with the actual asteroid or comet
actually hit the earth is a rebound that
creates a central peak and then they
tend to have REM structures or ring
structures around the rims of the crater
from where they are from the crater has
collapsed here is a photograph of a
simple crater from Mars ball-shaped
pretty straightforward 2,600 meters
across and the God line representing the
ejecta blanket that is surrounding this
crater
this is a photograph of a complex crater
on the moon 58 kilometres in diameter
this is a big one
you can see the central peak the ejecta
blanket surrounding the Creator ring
structures around the edge of the crater
again that is where the the rim of the
crater has collapsed and then also small
simple crater sort of surrounding it
from other impacts or perhaps even in
fact that came along with this major
impact from studying craters we've come
up with a pretty good estimation on the
crater versus the near-earth objects
sighs so an impact crater tends to be 10
to 20 times larger than the colliding
any oh so if a 10-kilometer near-earth
object hits the earth than the Creator
might be 100 to 200 kilometers across
and an example this crater in Canada and
we only have the remains of the crater
and the rock record the estimated ennio
was between five and ten kilometers in
diameter and it created a 100 kilometres
wide crater more than 150 impact craters
have been identified on earth couple of
them are identified in the oceans
typically ocean floors or less than 200
million years old and and those craters
have been obscured by other geologic
processes that are occurring on the
ocean floor but number three there just
off the Yucatan also part of the Gulf of
Mexico that is the the impact that was
thought 65 million years ago to have
caused the extinction of the dinosaurs
so the good news about these really big
near-earth objects is impacts expected
impacts are really very very
infrequently go back 65 million years to
the one in the Yucatan killed the
dinosaurs about a million years how to
an impact crater from large any oh and
the Chesapeake Bay and then about a
hundred years so the one that the meteor
crater that we saw in in Russia so
impacts of relatively small eneos 50
meters or less occurred intervals of
maybe hundreds
thousands of years but those large eneos
10 kilometres or more tend to be
measured on time scales in the hundreds
of millions of years and here is the
illustration of the potential
catastrophic events that would occur if
a 10-kilometer any Oh Clyde with earth
you know at the tsunamis while flyers
the air blast knocking trees down hot
fragments starting fires and then the
ejecta from the collision creating a
dust cloud and blocking out sunlight and
cooling the earth in the short . maybe
even years or tens or hundreds of years
but the short term in terms of the
geologic time scale so what would happen
in the 10-kilometer ennio collided with
earth doesn't look like it be very good
and these are some of the expected
events from a 10-kilometer ennio this
large fireball racing through the
atmosphere people at the impact site
with just seconds to live the air blast
with flat everything for hundreds of
kilometres in every direction a massive
earthquake at the collision site ocean
impact produce giant tsunamis hundreds
of meters high molten rock from the
collision would rain down starting
massive wildfires huge clouds of dust
the ejecta from the impact would block
out sunlight cooling the planet for
months killing almost vegetation and
then lots of gas from the impact sulfur
dioxide and water vapor will be added to
the atmosphere some scientists
hypothesize that in co impacts are
really the only major natural hazard
that we have the potential to prevent we
can't stop volcanoes earthquakes or
massive hurricanes but potentially we
could develop the technology to prevent
a major ennio impact with forewarning
eneos could potentially be deflected off
course or destroyed a scientists have
already hit a comment with the
spacecraft and landed a spacecraft on an
asteroid so it's not out of the realm of
possibility that given enough time we
could do something to deflect or destroy
an incoming any oh so because we'd like
to have that time that that forewarning
we have
seen organizations created to detect any
owes so current ennio search programs
focus on the approximately one thousand
objects with a diameter of more than one
kilometer in the heliosphere that we
think we are near Earth objects they
they're looking for fast-moving dark
objects against the backdrop of space
pumps they're pretty tough fine but
these largest eneos are the ones that
pose the greatest risk and because they
are so much larger they're easier to
find in the small ones and so they
really does make a lot of sense to look
for the small ones are basically just
looking for the big ones and scientists
map the position of those eneos overtime
and charter course relative to earth and
you know definitely making that that
effort to protect humanity from this
particular global catastrophe as I will
tell you many times in this course
scientists basically just classify
things if you were a shell scientists
should go to the beach you come back
with a thousand shells and you separate
all those shells into different piles
you classify them year-round shells you
have come chels you have read
challenging my chills and and so we talk
about impact eneos scientists want to
imp classify those impacts as well and
that scale is the Torino scale that
assesses asteroid / common impact
prediction so the trio scale of 0 is in
any oh and space will miss earth or burn
up in the atmosphere one it will pass
near Earth but extremely unlikely to
impact 224 minor chance of an impact 527
a serious threat of impact and eight to
ten certain collision and we don't have
anything above i think a one at this
time but nonetheless there are
scientists out there looking looking for
these any oh so this wraps up chapter 3
the next chapters chapter 4
it's a gut is significantly more content
associated with it is the study of plate
tectonics and plate tectonics is
considered to be the unifying theory of
geology on earth pretty much explaining
most geologic processes through plate
tectonics so it's a pretty important
chapter
make sure you have time to sit and watch
that lecture
it's gonna be a little bit longer than
this one
