Transcript Cosmic Catastrophes and Life on Earth Ron Buta University of Alabama

Cosmic Catastrophes and Life on
Earth
Ron Buta
University of Alabama
Dept. of Physics and Astronomy1
and
Alabama Paleontological Society2
1www.astr.ua.edu
2www.alabamapaleo.org
Extinction
A fact of life on Earth!
Implies calamitous events in our
planet’s history
The Major Extinction Events
Present-day: Holocene extinction event
65 Ma: Cretaceous-Tertiary Extinction Event - dinosaurs (50%
species survived)
205 Ma: Triassic-Jurassic Extinction Event - marine families,
archosaurs, therapsids, large amphibians
251 Ma: Permian-Triassic Extinction Event - biggest (10%
species survived)
360-375Ma: Late Devonian Extinction
440-450 Ma: Ordovician-Silurian Extinction
Causes of Mass Extinctions
Good theory should:
-explain all losses, not just particular groups
-explain why particular groups died, while others did not
-provide a mechanism to cause a mass but not a total extinction
-be based on events or processes that can be shown to have
happened
wikipedia
Mechanisms
-flood basalt events
-sea-level falls
-impact events
-sustained and significant global temperature extremes
-supernova or gamma ray burst
etc
Flood basalt eruption: responsible for Permian-Triassic extinction?
mantle plume
A supernova is the most violent type of cosmic event, a stellar
explosion. If one occurred near the Earth, what would happen?
“Now, I warn you, there are powers in the Universe beyond
anything you know.”
The Galaxy Being
The Outer Limits 1963
A supernova involves an intense burst of radiation. In a matter
of days, it can brighten from an ordinary star brightness to
outshine an entire galaxy!
Most supernovae detected are too far away to have any impact
on Earth. However, a nearby supernova could potentially
damage the Earth’s ozone layer through its production of cosmic
rays and high energy electromagnetic radiation.
There are two major ways to get a stellar explosion. One is
mass transfer onto a white dwarf, which produces a Type Ia
supernova. This the most luminous type known.
The other type involves core collapse in a massive red or blue supergiant
star (Type II SN). A shock wave ejects the envelope gases, leaving behind
a neutron star (pulsar).
Exceptionally massive stars can explode as a hypernova,
The core collapses directly to a black hole. A disk of gas forms around the
hole if the star was rotating beforehand.
Material moves at almost light
speed out of the poles of the
gaseous disk after the violent
collapse. When this material
collides with the expanding
gases, we would see a gamma
ray burst.
The burst could affect Earth
only if it points in our direction.
A direct hit from a hypernova
within 3,000 light years could
“wipe out all life on the planet”
(Armageddon online).
The Large Magellanic Cloud is one of the nearest galaxies.
It is about 150,000 light years away.
In 1987, a blue supergiant in the Large Magellanic Cloud exploded as a
Type II SN. It was detected in a burst of neutrinos as well as visible light.
after
before
SN 1987A occurred in a huge star-forming region full of young,
massive stars.
The expanding gases formed several rings from interaction
between the fast moving gases and slower moving gases ejected
in an earlier outflowing wind.
Over time, a large expanding nebula of gases is seen as a
supernova remnant. This is the remnant of Tycho’s
supernova, seen in 1572.
A supernova probably blew the big cavity in this nebula in
the Large Magellanic Cloud.
A naked eye SN recorded in 1054AD
in the constellation Taurus.
The Crab Nebula is the remnant of the SN seen in 1054AD.
Most supernovae are seen in other galaxies
A SN in the “Black-Eye” Galaxy.
Supernova discovered by me!
Before (~1950)
After: May 25, 2001
Supernovae seen in very distant galaxies.
Two supernovae at once!
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Supernovae: what is the threat?
The most serious threat from a nearby SN is ionizing
radiation in the form of cosmic rays and gamma rays. These
have the potential to damage Earth’s ozone layer, exposing
living organisms to dangerous solar UV radiation.
A SN can cause mass extinction by a disruption of the food
chain at a low level, by destroying photosynthesizing
organisms. This is a side effect also of a large impact or
volcanic episode.
Ozone = O3
The ozone layer at 15-35 km up is our “UV shield.”
Cosmic rays are accelerated in the blast waves of supernovae, which
are expanding clouds of gas and magnetic fields. Gamma rays may be
produced in an intense burst when light-speed material collides with
the original expanding bubble.
A typical cosmic ray can cause an air shower of exotic
particles. A gamma ray encounter can also produce an
air shower.
Cosmic rays are 90% protons, 9% helium nuclei, 1% electrons
A simulated cosmic ray air shower
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Ionizing radiation can induce a chemical reaction that converts
atmospheric nitrogen into nitric oxide, NO. NO reacts with
ozone to produce NO2. A single NO molecule can catalyze a
reaction that breaks up 100,000 ozone molecules. This
depletes the ozone layer and its protective blanket around the
Earth.
How close might a supernova be and do this? If one exploded
within 30 light years (10 parsecs), it could have a serious
impact.
Expect one or more SNe within 10pc within past 570 Myr
Typical SN would appear more than 200 times brighter than
full moon at such a distance (Ellis & Schramm 1995)
Where do we run the most risk of encountering a massive star
that might explode?
One way is to get too close to something like this, called an “HII region”.
This could happen if the Sun passes through a spiral arm.
Right now,
the nearest
HII region is
the Orion
Nebula,
1,600 light
years away!
The Sun would pass through a spiral arm once every 100
Myr or so, and stay in the arm for maybe 10Myr. No
periodicity like this in extinction records, so SN extinctions
are not the bulk of known extinctions (Ellis & Schramm
1995).
Are there any good candidates for a nearby supernova explosion?
We can identify a few massive stars that might explode near
us, as a type II supernova or hypernova.
Type Ia supernovae are much harder to assess - we can’t see
the binary systems well enough to decide if a threat exists.
Betelgeuse is a top candidate and may explode within a few
thousand years. It is a red supergiant 640 light years away. Its
mass is 20 times that of the Sun.
---------->
Its pole does
not point
towards us, so
we would not
see a gamma
ray burst if it
explodes.
Eta Carinae is one of the most massive stars in the Milky Way, about 100150 times the Sun. It emits 4-5 million times more light than the Sun. It is
more than 7,000 light years away and will probably explode as a hypernova
within 50,000 years.
---------->
In 1843, Eta Carinae suffered an outburst that made it the
second brightest star in the sky for a while. A huge amount of
matter was expelled.
On what basis might we deduce that a supernova or
hypernova might have caused a mass extinction?
Did a supernova contribute to extinction of the mammoth?
Firestone & Allen 2005- SN 41,000 years ago, 250 light years
away. Iron-rich grains impacted Earth 34,000 years ago and
pitted mammoth tusks. SN debris coalesced into comet-like
objects; one impacted Earth 13,000 years ago.
Ordovician-Silurian Extinction - 450-440 Ma
3rd largest
>100 families of marine invertebrates died, including 2/3 of all brachiopods
and bryozoans; corals, bivalves, and echinoderms also were affected
Immediate cause: continental drift of significant land mass over south pole,
causing a global temperature drop
Gamma ray burst from hypernova 6,000 light years away suggested to strip
half of ozone layer, killing surface organisms with deadly UV, affecting
photosynthesis, and causing temperature drop
Nankinolithis sp.
Caleidocrinus multiramis
The Scorpio-Centaurus Association, a lose
collection of nearby, massive stars.
Alpha Centauri
Southern Cross
This area may have produced a recent nearby supernova.
2 million years ago, Sco-Cen was 130 light years from
Earth.
-SN in this association when it was near explains
discovery of Iron-60 atoms in ocean floor cores
-This rare isotope of iron came as fallout and may have
helped extinguish some marine molluscs.
-Blast of cosmic rays could generate enough ions to
damage ozone layer
-Damage may have lasted 100-1000 years
Which is the worst cosmic catastrophe?
A supernova/hypernova?
Or an asteroid impact?
An asteroid has been implicated in the K-T extinction
event owing to high levels of iridium in the K-T
boundary layer.
A big asteroid impact would:
-scatter dust and debris in atmosphere, blocking sunlight for
months
-cause huge fires and trigger volcanic eruptions
-trigger tsunamis and high winds
-cause acid rain
-disrupt the food chain
Alvarez & Alvarez 1980
A nearby SN explosion at 10 parsecs would:
-not significantly heat the Earth
-not harm ecology by its excessive optical brightness
-not have serious effect on Sun’s energy output
-kill some organisms directly via increased UV admitted after
destruction of the ozone layer
-indirectly kill others that depended on those organisms
-cause no dramatic environmental effects like those caused by
meteorite impact or massive volcanism
Ellis & Schramm 1995
The bottom line:
-the biggest threats to life on Earth are likely more local than any
exploding star might ever be!
Final words of wisdom: “There are powers in the Universe,
inscrutable and profound. Rage cannot help us. Fear cannot save
us. We must view the stranger in a new light - the light of
understanding, and in order to achieve this, we must understand
ourselves, and each other.” The Galaxy Being, The Outer Limits,
1963
This presentation was based on extensive internet research, especially Wikipedia.