Transcript The Evidence for Terrestrial Impacts Throughout Geological

The Evidence for Terrestrial
Impacts Throughout
Geological History
Kate Yohay, Jess Yamane,
Tram Nguyen, & Courtney
Patterson
World Map of Large Impacts
Europe
Crater: Mjolin, Location: Norway
Crater: Dellen, Location: Sweden
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http://www.unb.ca/passc/ImpactDatabase/europe.html
South America
Crater: Monturaqui, Location: Chile
Crater: Araguainha, Location: Brazil
Crater: Chixculub
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http://www.unb.ca/passc/ImpactDatabase/SAm.html
Africa
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http://www.unb.ca/passc/ImpactDatabase/africa.html
Asia
Crater: Logancha, Location: Russia
Crater: El'gygytgyn, Locaction: Russia
http://www.unb.ca/passc/ImpactDatabase/asia.html
North America
Crater: Chesapeake Bay, Location: Virginia, USA
Crater: Barringer, Location: Arizonia, USA
Crater: Upheaval Dome, Location: Utah, USA
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http://www.unb.ca/passc/ImpactDatabase/NAmerica.html
Australia
Terrestrial Impacts on Other Bodies in the
Solar System
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The surface of the Moon, Mercury, and
Mars, where geologic processes have
halted millions of years ago, record
terrestrial impacts, thus it is beneficial to
understand impacts on other solar bodies
in the solar system in order to understand
terrestrial impacts on Earth.
In relation to The Moon
• The Earth has been the target of impacting objects
about 10 times more than the Moon, yet much less
(about 160) has been discovered.
• Earth, which has been more heavily impacted than the
Moon, is covered with craters that are continuously
becoming less evident due to erosin, redeposition,
volcanic resurfacing, and tectonic activity. The moon has
neither an atmosphere nor water, thus the components
in the soil do not weather away chemically as they
would on Earth.
• The far side of the Moon, in relation to its position facing
the Earth, has more craters than the near side because
the side facing the Earth is shielded by the Earth.
In Relation to Mercury
• Mercury has no tectonic plates like Earth.
• Mercury is covered by craters that are either
classified as intercrater plains or smooth
plains, which have been effected by volcanic
activity.
• After the intense bombardment period (about
4.5 billion years ago), volcanic lava covered
the older crust, thus forming the intercrater
plains. The lava makes the intercrater plains
less saturated with craters and makes the
craters appear smaller in size (less than 15 km
in diameters).
• The smooth plains are even younger, with less
craters due to volcanic lava that has further
filled the craters.
Mars
• Mars has symmetry about its equator dividing the planet
into the old and young hemispheres.
• The older terrain in the southern hemisphere is heavily
cratered.
• The northern hemisphere has less craters than the
southern hemisphere, possibly due to volcanic flows.
• Although no one knows exactly why there is a difference
between the crater impacts of the two regions, it has
been proposed that volcanic plains, huge crustal uplifts,
and volcanic shields (i.e., mountains) dominate the
northern hemisphere, and thus covers up the potential
craters that may have existed there.
A Consequence of Asteroid
Impact: The Death of the
Dinosaurs & End of the
Mesozoic Period
“Approach of Doom”
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Either comet or asteroid about 10 km across
traveling @ an estimated velocity of equaling
30km/s
That would make it as wide as San Francisco
and taller than Mt. Everest w/ a volume
greater than that of all the buildings in the US
put together
It would have a destructive equivalent to that
of 100 million hydrogen bombs and it’s
impact would equal an explosion caused by
100 million megatons of TNT
Aimed at what is now the Yucatan Peninsula
of Mexico
Moment of Impact
95% of the Atmosphere lies below an altitude of 30
km so depending on the velocity and angle at which
the asteroid/comet approached the surface it would
have taken 1-2 seconds to penetrate most of the
atmosphere
Compression heated the air instantly to 4-5x’s that
of the sun generating a searing flash of light
At the instant of contact with the Earth’s surface
where the Yucatan Peninsula lies, 2 shock waves
were triggered
1st shockwave plowed forward into the bedrock
passing through a 3km thick layer of limestone near
the surface and down into the granite crust beneath
and crushing shut cracks and pores and destroying
much of the crystal structure of minerals
2nd shockwave: flashed backward into the onrushing
comet/asteroid reflecting of the back of the body
tearing apart its spherical shape
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•Because it’s moving so fast the asteroid/comet would have caused a
shock wave, a sonic boom
•This compressed the target so intensely that after the shock wave, the
decompressing rock flew apart, melted, or vaporized
•Whole continents caught fire though firestorms may not have been
intense on other continents as N. America
•The Earth’s surface became a broiler: cooking, charring, igniting and
immolting trees and animals not under rocks/ in holes but in a less
immediate area
•A gigantic tsunami (about 1km high) spreading outward and across the
Gulf of Mexico digging channels in the fine sediment on the sea floor and
mixing it w/ impact debris
•The Tsunami confined to Gulf of Mexico/Florida area.
Aftermath
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W/in days fires and wind were dying and Tsunami was
spent, but the Earth was becoming dark and cold
In the zone where bedrock was melted/vaporized no living
thing could have survived even w/in a radius of 100km
Fine dust from the comet/asteroid settled through the
upper atmosphere around the world and blocking out the
sunlight –lasted for a few months
The greenhouse gases, water vapor and carbon dioxide,
were released raising temperatures above normal levels for
probably thousands of years
Acid rain was formed from sulfur in the limestone in the
Yucatan area
Nitrogen gas breaks up when in extreme temperatures,
thus vast quantities of NO were produced which would form
nitric acid when in gaseous form killing plants and animals
and dissolving rock when it rained
Retrospect
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180 km wide collision scar “the great ‘K-T’
mass extinction”
Chicxulub crater
Peligic limestone (neritic limestone is built
up by fossils of organisms that live on the
sunlit bottom of shallow water) are
sediments that are deposited in the
darkness of the deepest eroding waves
and lie undisturbed for 10’s of millions of
years
The Barringer Meteorite Crater
aka Meteor Crater
•Occurred 50,000 years ago during an ice age
•Arizona: Cool wet forest
•Inhabited by mammoths, mastodons, giant ground sloths, bison
•Impact blast caused local extinction providing a new habitat for other
plants and animals
•The bowl shaped depression filled with water creating a fresh water
lake for vegitation and aquatic animals
Evidence
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During the early 1900s there was a race to see who could
prove the cause of the crater
The leading theories, provided by Grove Karl Gilbert stated
that the crater was either formed by a meteorite or that it
was the result of a massive explosion of steam produced by
volcanic heat at a great distance below the surface.
No evidence of volcanic rock was found in the area
Barringer’s papers were based on observations Gilbert
made but whose significance Gilbert had missed
Barringer’s Findings
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The presence of a vast amount - probably in the millions of tons - of finely pulverized
silica. The pressures required to produce such a material, Barringer argued, were too
great to be the product of any known volcanic force.
The large quantities of magnetic iron oxide, in the form of globular "shale balls",
scattered around the rim and the surrounding plain. Some of the large balls, when
split open, displayed the "Widmanst䴴en patterns" characteristic of iron meteorites.
Much of the rest consisted of a fine blackish-gray powder, crystalline in structure,
"with intensely fine grains of silica powder adhering so closely to its surface as to
suggest adhesion." This powder, Tilghman noted, was "not a constituent of any of the
rocks in the neighborhood", and furthermore was "different from any terrestrial
magnetite known."
The random mixture of chunks of meteoritic material with the ejected rocks on the
crater rim, and its symmetrical distribution around the crater, both of which
demonstrated that the material must have been deposited simultaneously with the
creation of the crater.
The fact that the different types of rock in the rim and "ejecta blanket" (material
thrown out of the crater) appeared to have been deposited in the opposite order from
their order in the underlying rock beds - as if the beds themselves had been
overturned.
The absence of any naturally occurring volcanic rock in the vicinity of the crater.
Regarding Gilbert's failure to find any magnetic anomalies, Tilghman noted that while
the presence of a single large mass of iron should produce such an anomaly, a mass
of small magnetized fragments would not. He found it difficult to discuss Gilbert's
steam explosion hypothesis, since no one had ever seen or known of such a process
in actuality, except in association with an ordinary volcano. (Hoyt, pp. 89-99)
Tunguska
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June 30th, 1908 “something” exploded 8
km high on the river Stony Tunguska
destroying 2,150 km^2 of Siberian taiga
Fires burned for weeks destroying
1,000km^2
“Ash and powdered tundra fragments
sucked skyward by the fiery vortex were
caught up in the global air circulation and
carried around the world. Meanwhile,
bursts of thunder echoed across the land
to a distance of some 800 kilometers. “
(Southworth Planetarium)
Unclear whether it was a comet or
asteroid
Tunguska region in 1938:
Portion of one of the photos from Kulik's aerial photographic survey
(1938) of the Tunguska region.
The parallel fallen trees indicate the direction of the blast wave
.
Effects
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Following the explosions unusually colorful
sunsets and sunrises were reported in W.
Europe, Scandinavia, and Russia
Magnetic “storms” similar to ones
produced by nuclear test explosions in the
atmosphere occurred 900km southeast
Following the blast there was accelerated
growth of biomass in the region of the
epicenter as well as an increased rate of
biological mutations