Fw: Re: Researchers: Comet, not asteroid, wiped dinosaurs out

This is a post of mine on another group.  John W.


>
>So it was a comet that did in the dinosaurs 65 or 66 million years ago, at the Cretaceous-Tertiary boundary? (K-T Event).? 
>
>
>
>Comets, which are believed to be Kuiper Belt (short-period, with highly 
eccentric elliptical orbits) or Oort Cloud (long-period, with almost 
parabolic orbits) objects, that have been knocked into highly eccentric 
orbits by collisions, usually consist mostly of volatile materials 
especially water. This accounts for their developing "tails" due to loss of some of their material when close to perihelion, eventually entirely 
evaporating except for any higher-melting solids, and in some cases for 
their breaking-up on close approaches to the Sun or Jupiter (for example Comet Shoemaker-Levy, which several years ago broke up, and then its 
fragments spectacularly collided with Jupiter).
>
>
>However, the fact that iridium and other platinum-group metals (osmium, platinum, ruthenium, rhodium, palladium), which are rare 
in Earth's crust but much more abundant in Earth's core and in metallic meteorites (composed mainly of iron, nickel, and cobalt, with smaller 
amounts of other heavy metals) and mixed stony-metallic meteorites, have been found in elevated concentrations in sediments deposited on and 
radioisotope-dated to the Cretaceous-Tertiary boundary, 
definitely points to such an impacting asteroid, thought to have been 
about 6 miles or 10 km in diameter from the size of the Yucatán crater. 
If it was a comet, it must have had an abnormally large composition of 
heavy metals, which for a normally icy Kuiper Belt or Oort Cloud object would be most unusual.
>
>
>The year of the Cretaceous-Tertiary impact that did in the 
dinosaurs has been very recently (Feb. 2013) narrowed down to 66,038,000 ±11,000 
years ago, by potassium-40-argon-40 
radioisotope dating of samples found at the stratigraphic boundary 
between the Cretaceous and Tertiary. Potassium-40 decays with an half-life of 1.248×109 years, somewhat more than 1/4 the age of Earth, to a mixture of Calcium-40 (89.1%) and argon-40 (10.9%), the argon being trapped in solidified rocks especially granite; see http://en.wikipedia.org/wiki/K%E2%80%93Ar_dating for details of the technique.  The 180-mile diameter crater that 
the impact left at Chicxulub, Yucatán, México, has been almost 
completely obscured by subsequent erosion and deposition of sediments. 
See: 
>http://www.spacedaily.com/reports/New_evidence_suggests_comet_or_asteroid_impact_was_last_straw_for_dinosaurs_999.html
>
>See also:
>http://en.wikipedia.org/wiki/Cretaceous–Tertiary_extinction_event
>http://en.wikipedia.org/wiki/K–T_boundary
>http://serc.carleton.edu/research_education/cretaceous/ktboundary.html
>http://www.teara.govt.nz/en/geology-overview/6/3
>http://geopubs.wr.usgs.gov/open-file/of01-056/of01-056.pdf
>http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19970015333_1997024631.pdf
>http://www.sciencemag.org/content/294/5547/1700.abstract
>http://geology.geoscienceworld.org/content/19/9/867.abstract
>http://www.sciencedaily.com/releases/2008/04/080424140400.htm
>http://geology.geoscienceworld.org/content/14/12/1024.abstract
>http://esp.cr.usgs.gov/info/kt/boundary.html
>http:////www3.geosc.psu.edu/people/faculty/personalpages/tbralower/Braloweretal1998.pdf
>http://geoweb.princeton.edu/people/keller/kelleresr62.pdf
>http://esp.cr.usgs.gov/info/kt/stop1.html
>http://nmgs.nmt.edu/publications/guidebooks/downloads/56/56_p0395_p0407.pdf
>http://miac.uqac.ca/MIAC
>http://www3.geosc.psu.edu/people/faculty/personalpages/tbralower/Goto.pdf
>http://books.google.com.au/books/about/The_Cretaceous_Tertiary_event_and_other.html%3fid=kAup0TOL09gC
>
>Dinosaurs first 
arose in the Triassic, and then lived through the Jurassic and 
Cretaceous (at the boundaries between which the impacts must have been 
relatively minor), steadily increasing in body size and specialization 
until their final extinction. Toward the end of their dominance on 
Earth, by the late Cretaceous considerable attenuation of their species 
had occurred, with only 7 genera remaining at the end. This was probably
 due to a combination of excessive body size (which probably made the 
last pterosaurs, of which only two species survived to the very end of 
the Cretaceous, simply too heavy to fly, noting that weight increases with the cube of size but aerodynamic lift increases only with the square of size), excessive specialization and 
hence inability to adapt to changed environments, and competition by 
early mammals and birds (which arose in the Cretaceous and survived the asteroid impact).
>
>
>Other geological period boundaries, such 
as Devonian-Carboniferous, Carboniferous-Permian, Permian-Triassic, 
Triassic-Jurassic, and Jurassic-Cretaceous, are also likely to have been caused by meteorite impacts of varying severities. For example, the one that created the Sudbury basin in Ontario, Canada, where iron, nickel, 
cobalt, copper, and platinum-group metals, probably of meteoritic origin, are 
mined, is believed to be about 1 billion years old.
>
>John W.
>
>
>----- Forwarded Message -----
>>From: Greg Dempsey <[email protected]>
>>To: Greg dempsey <[email protected]> 
>>Sent: Sunday, 24 March 2013 4:43 PM
>>Subject: *? 2 ALL: RESEARCHERS: COMET, NOT ASTEROID, WIPED DINOSAURS OUT - WHAT ARE YOUR COMMENTS?*
>> 
>>
>> 
>>
>>
>>Hi Team!
>>*? 2 ALL: 
>>RESEARCHERS: 
COMET, NOT ASTEROID, WIPED DINOSAURS OUT -  Arturo Garcia reports:
>>'New research points to a comet as 
the source of the explosion that caused the extinction of dinosaurs, 
contradicting earlier theories blaming an asteroid. 
>>"Science Recorder reported on Fridaythat the findings from a team at Dartmouth College indicated that an asteroid 
would not have been capable of creating the Chixulub crater in Mexico, long regarded as the collision point for 
the phenomenon that led to the destruction of 70 percent of animal species on 
the planet 65 million years ago.
>>"Lead study author Jason Moore and 
his fellow researchers presented their findings at the annual Lunar and Planetary Science Conference. 
>>"Moore said an analysis of iridium 
and osmium layers within the 180-kilometer wide crater revealed that the crash 
created less debris than an asteroid would have been able to 
produce.
>>“'You’d need an asteroid of about 
5km diameter to contribute that much iridium and osmium,' Moore said. 'But an 
asteroid that size would not make a 200km-diameter crater. So we said: how do we 
get something that has enough energy to generate that size of crater, but has 
much less rocky material? That brings us to comets.'” (continued below)
>>Researchers: 
Comet, not asteroid, wiped dinosaurs out - what are your 
comments?
>>Greg Dempsey 
>>http://groups.yahoo.com/group/SECULARHUMANIST/
>>Voice of the 
People
>> 
>>=======
>> 
>>Researchers: Comet, not asteroid, wiped dinosaurs 
out
>>By 
Arturo Garcia
>>Raw 
Story
>>Saturday, March 23, 2013 
20:36 EDT
>>...The two elements, Moore 
said, could not have been generated within the crater 
naturally.
>>However, a researcher at 
Imperial College in London told the 
BBCthat 
though the Dartmouth team’s work was “thought-provoking,” it did not entirely 
shut the door on possible asteroid involvement.
>>“The authors suggest that 
75 percent of the impactor mass is distributed globally, and hence arrive at 
quite a small-sized impactor,” said Gareth Collins “But in reality this fraction 
could be lower than 20 percent.”
>>
>>
>
>

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