Submission to annual undergraduate writing colloquium contest
Diego Alberto Vasquez
2011 – Geological Sciences, Geochemistry Track
EES 393 – Senior Thesis
Natural and Applied Sciences
Detecting extraterrestrial trace material from suspected impact and known boundary layers using geochemical analyses
Diego A Vasquez
Senior Thesis
Department of Earth and Environmental Sciences
University of Rochester
Abstract
Impacts of extraterrestrial origin have had major influences on the history and evolution
of our planet. Previous research has shown that examinations of particles with unusual chemical
compositions, isotopic ratios and morphological components, relative to the crustal earth, have
served as concrete evidence for extraterrestrial signatures on Earth. Optical and compositional
analysis of magnetic sediment extractions with unusually elevated concentrations of metallic
unoxidized trace element-rich grains are extremely rare in terrestrial environments, and thus
also serve as solid proof of cosmic intrusions. Reports on noble gas and mineralogical data,
among other sources of evidence, have suggested that the Younger Dryas event (~13,000 years
ago) which is distinguished by a serious abrupt change in climate and significant mammalian
extinctions has been associated with an impact event or series of events. Similarly, the Tunguska
event is also presumed to have been caused by an extraterrestrial explosion. Sediment samples
from these two suspected impact events have been examined by using distinct methods of
chemical, physical and optical analysis to discern trace evidence. Furthermore, using the same
geochemical procedures, we have also included sediment from a possible comet impact site in
Eastern Europe which may be used as additional supporting data.
Introduction Analytical examination of sediment samples from suspected extraterrestrial impacts
involve searching for physical and chemical clues of cosmic intrusions within the Earth. Since
the chemical composition of the cosmos differs significantly from our terrestrial composition,
impact events are often identified by chemical fingerprints distinct from the earth’s normalized
elemental proportions. It is therefore possible through scientific research to identify when there
have been interactions of comets, asteroids, meteorites and other celestial bodies with the earth.
Impacts of astronomical origin can have serious effects on the chemistry of Earth’s oceans and
atmosphere while at the same time altering our natural biogeochemical cycles, causing many
disruptions to ecological balances of life on earth. Some examples of the effects of these
powerful astronomical acts can include: disruption of thermohaline circulation if polar
explosions generate enough heat to melt the ice sheets, change in wind currents and atmospheric
chemistry by atmospheric loading of dust, debris and other sun-blocking particles, depletion of
the ozone layer by thermal/chemical interactions and dramatic fluctuations in climate
temperatures1. Also, additional indirect consequences that may result from a large impact and its
shockwave may include: severe acid rain, wildfires, changes in precipitation patterns, increased
seismic activity and other environmental repercussions2. Impact events have proven to
significantly shape the evolution of our world throughout the past by various means, examination
of these past occurrences and their magnitude of disruptions can help us better understand the
potential effects they have on Earth and on scientific knowledge.
Background and Related Information
At around 13,000 years ago the Earth experienced a drastic change in climate
distinguished by a rapid return to glacial conditions. This environmentally dramatic episode is
referred to as the Younger Dryas event occurring during the end of the Pleistocene epoch. The
event occurred in a geologically minute timescale; nevertheless, many unexplained phenomena
during this time led to major ecological instability and widespread extinctions3. A variety of
theories have been proposed to explain the resulting event, including that: A Supernova
explosion occurred around 44,000 years ago, the debris-laden shockwave of explosion reached
the Northern Hemisphere in a series of extraterrestrial impacts and/or bolide explosions at the
beginning of the Younger Dryas episode triggering the event4. During this epoch in time there
were pervasive extinctions that occurred including the extinction of the North American
megafauna and Paleo-Indian cultures. Some of those extinct colossal mammals that mysteriously
disappeared during this time include: woolly mammoths, saber-toothed cats and mastodons5. The
cause(s) of these extinctions are still not clearly understood, however, ecological instability
triggered by an impact may have been the underlying factor. This era of time is recorded on the
Earth as a dark, carbon-rich stratigraphic layer known as the “black mat.”6. In our examinations
we have included various samples of this mysterious layer from different locations in North
America. Another perplexing event that we have incorporated into the research analysis is the
1908 Tunguska explosion in which we have also included a series of samples from this location
in Siberia. Although the exact cause of the explosion is still under investigation, it is generally
accepted that it was the result of an airburst of a celestial body releasing massive amounts of
energy7. Estimates of the amount of energy released from the air burst are between 10-20
megatons at an altitude between 5-10km, destroying over 2,000 km2 of forest
8. An explosion of
this magnitude would have severe consequences on the environment and surrounding ecosystems,
especially if the devastating act occurred over an inhabited area. As a supplement to the two
incidents mentioned above we have also included sediment from a third source, suspected comet
debris from Eastern Europe in which we will investigate using similar procedures and methods.
Geochemical Implications
Chemical occurrences originating from the initial formation of our solar system have
enabled scientists to discover solid proof of cosmic intrusions within our modern-day earth;
many of these clues are in the form of isotope abundances, chemical anomalies and distinct
mineralogical compositions. From the very first nuclear fusion between hydrogen atoms to form
helium, to subsequent nucleosynthesis reactions producing most of the elements known in the
universe and to the formation of planets by accretion, scientists have been able to distinguish
between the distinct chemical characteristics present in our solar system. The very first mineral-
forming elements that condensed from our early solar system were refractory metals that reacted
with the hot gases present in our ancient solar nebula to form metallic oxides. These metallic
oxides eventually alloyed with nickel and began condensing to form planetary cores, including
earth’s peculiar core9. It was during our planet’s early formation that a special group of elements
with very high chemical affinities for iron, known as the Platinum Group Elements, efficiently
condensed with metallic Fe-Ni in earth’s core9. Because of the geochemical characteristics of
these siderophile noble metals such as: high resistance to oxidation and very high melting points
yet low vapor pressure relative to iron, they were and are still effectively sequestered in earth’s
liquid outer core and solid inner core, and thus are very scarce in earth’s crust. Meteorites which
preserve most of these noble metals reflect solar system abundances about one million times
higher than the crust. Since these concentrations are much higher in extraterrestrial material than
in planetary silicate crust, PGE’s serve as exceptional tracers of extraplanetary cosmic dust or
meteoritic impact material10
. PGE’s are usually expressed in concentrations relative to
carbonaceous chondrites; iron meteorites (which serve as analogous to earth’s core) typically
have 10-20 times average chondrite values and most crustal rocks contain <0.001 times chondrite
values11
.
It is also possible to distinguish between the different chemical characteristics of our
solar system by examining the components of the interplanetary medium and their interaction
with our planet. Our planet is protected from most interstellar radiation by our terrestrial
atmosphere and magnetic field, this however, is generally not the case for celestial bodies and
extraterrestrial particulates, which are stripped of atmosphere and generally lack any significant
magnetic fields. Since our galaxy is threaded with cosmic rays and other interplanetary medium
particulates, extraterrestrial bodies like asteroids and meteors (which have no natural “shields” as
mentioned previously) are constantly bombarded by these cosmic particles and thus have much
higher abundances of specific atomic nuclei. Different isotopic ratios of “cosmogenic nuclides”
exist for celestial bodies when compared to terrestrial bodies; among the stable cosmogenic
nuclei, those of the rare gasses are some of the most easily measured12
. 20
Ne/22
Ne and
3He/
4He
isotope ratios on earth have much smaller proportions compared to external celestial bodies. The
main source of ET noble gases is from solar wind implantation, embedding them with a solar
signature representing “cosmic” abundances, however, many meteorites (mainly undifferentiated
meteorites such as carbonaceous chondrites) have a distinct “planetary” signature representing
the terrestrial atmosphere, being enriched in heavier gases (Xe, Ar, Kr) relative to He and Ne. So
if measured values are closer to the “planetary” pattern (as opposed to the prevalent solar
component associated with most ET noble gas accretion to earth), then the data could imply that
an impact (with an undifferentiated parent body) preceded. Another important fact to mention is
that extraterrestrial material usually degasses during atmospheric entry and/or collision with our
surface due to thermal ablation and fragmentation, therefore lack of heating is essential to
preserving the gases. Generally only particles that are <20 m reach stratosphere without
substantial modification from heating during entry/impact, this strongly restricts the retention
potential of ET gases and makes very fine-grained particles in sediments the dominant inventory
of ET noble gases. Also, if measured isotopic values are consistent with the near-constant flux
of extraterrestrial 3He, then it is indicative that the celestial body associated with the proposed
impact was not accompanied by increased solar system dustiness, so therefore could not have
been member of a comet shower. Noble gas data at boundary layers have served as secondary
evidence to complement additional data in support for impact hypotheses. Of the monatomic
noble gases, 3He is the most distinguishable to characterize because it’s only present on earth in
trace amounts and it is far more abundant in stars and in space. Virtually all of the 3He in the
surface of the earth comes from a primordial source, mostly from the constant flux of
interplanetary dust particles (IDP’s) implanted by solar energetic particles and galactic cosmic
ray bombardment13
. Measuring the isotopic ratios and 3He concentrations between the different
layers can give us an idea of the rate of accretion of the ET particles, and although large ET
bodies can account for accretion of significant quantities of ET debris over short periods of time,
simply finding anomalous peaks of 3He and/or
20Ne would not necessarily entail an impact event,
differences in isotopic ratios could signify variations in accumulation rates. On this note, 4He
is a
radiogenic daughter product resulting from alpha decay of uranium and thorium and other
relatively abundant crustal elements; this continuously affects the 3He/
4He ratio within the crustal
environment and further minimizes the near-negligible concentration of primordial helium
present in our atmosphere. Also worth mentioning is that helium leaking from the earth during
volcanic processes feeds the atmosphere but ultimately escapes to space because it’s chemically
inert and very light. Additionally, we have separated our samples into three different fractions:
magnetic, carbonaceous and siliceous, in order to get an idea of the main carrier phase of the
accretion of extraterrestrial noble gases to the earth. The distinct proportions of the noble gas
isotope ratios we get from the different sample layers and fractions will help us discern the
nature of events related to the sampled locations.
Another way to investigate samples in search of impact particles of extraterrestrial origin
is to search for microscopic deformation and melting features. Distinct geochemical signatures
present in the samples provide scientists the ability to speculate on their provenance; specifically,
magnetic separates, cosmic micro-spherules and carbon impactites allow us to verify their origin.
One exceptionally clear indicator present in sediment samples of extraterrestrial origin which
does not occur naturally in any terrestrial environment and which has only been found in
association with known impact events, is Nickel-bearing magnetite14
.1-20 micron magnetic Iron
Oxide crystals with significantly higher concentrations of Nickel are precise ET markers which
have served as undisputable proof in samples from the K/T boundary (Dinosaur extinction) and
in the Late Eocene comet shower where large concentrations of these peculiar minerals have
been found in the very restricted stratigraphic distributions15
. Additional “cosmic spinels”
resulting from recrystallization and melting of incoming material with anomalously high Ni, Mg,
Al and Cr compositions combined with low or nonexistent abundances of Titanium distinguish
these minerals from terrestrial counterparts16
. Also another peculiar characteristic of cosmic
spinels is their common skeletal or honeycomb morphology, which is indicative of rapid cooling
from a vapor cloud after impact16
. Similarly, magnetic cosmic spherules are also good impact
indicators; they are rounded particles of extraterrestrial origin that are for the most part solidified
fragments of meteoroids which are formed when entering Earth’s atmosphere at super-high
velocity or hypervelocity resulting from an explosion. When entering the atmosphere they
interact with air particles resulting in frictional heating, melting and subsequent quenching in the
atmosphere’s relative low temperature17
. Distinction between crustal and ET microspherules can
be done by using some elemental ratios between Fe versus Ti, Cr, Mn, Co and Ni 18
. Soil samples
from drill holes and trenches acquired from Tunguska had significant amounts of these tiny
spheres of meteoritic dust that had shed off from the incoming body as molten droplets and
solidified19
. Magnetite, an iron oxide mineral, was present in many of the spheres; it typically
forms on the exterior of a meteoroid as it ablates in our oxygen-rich atmosphere19
. Not all
spheres are made up primarily of iron; some can be glassy, composed of silicate minerals that are
typical of stony meteorites. Some of the spheres from Tunguska were even composed of both
types, pointing to the possibility that the body was made up of a mixture of ice and metallic and
silicate chunks, perhaps signifying a comet-like body. Discoveries such as these plus the fact that
no crater has been found in association with the Tunguska event reflect the strong likelihood of
an airburst of a comet-like body instead of an impact with the surface of the earth19
. Significant
amounts of cosmic Iron-spherules have also been found in the black mat from the Younger
Dryas4. Abundances of cosmic spherules in sampled layers could be strong indicators of
increased meteoroid infiltrations in our atmosphere.
Carbon impactites are an additional source of evidence that we could use. During violent
extraterrestrial impact events, the surrounding environment experiences massive increases in
temperature and pressure dispersing energetic shockwaves in the area and thus enabling shock-
metamorphism to take place in rocks and sediments, which leaves distinct impactites and other
significant impact-derived components. Among these impactites are included: tektites, shocked
mineral grains, diamonds, shatter cones, impact breccias and the geochemical signatures
mentioned previously in this report20
. A good ET indicator would be to find abundances of
nanodiamonds present in glass-like carbon molecules, nanodiamonds are formed by energetic
explosions in space. Diamonds can only form under high-pressure/high-temperature
environments; impact events enable shock zones with the right range where graphite transforms
into diamond. One peculiar and extremely rare type of nanodiamond, hexagonal nanodiamonds
(or N-diamonds), do not occur naturally in any known terrestrial environment and have only
been found in association with impact-related sites and synthetically produced in laboratories21
.
Therefore, finding these preternatural hexagonal nanodiamonds in the crust with any of these
samples would serve as definite proof of impact. Under these intense conditions other shock-
related metamorphism takes place such as: shocked quartz and the metamorphism of silicon
dioxide into coesite and stishovite20
. Other potential tracers can also include carbon allotropes
like fullerenes, nanotubes and amorphous carbon.
Methodology
The key principle underlying the methods of analysis utilized in this project strongly
emphasized in looking for any trace material that is exceptionally uncommon in crustal
environments but relatively common in extraterrestrial material, especially Nickel in Electron
Microscopy, Iridium in Laser ICP-MS and 3He in Noble Gas-MS. The methods used include:
Noble Gas Mass Spectrometry to measure bulk sediment, magnetic separates and carbonaceous
residue to determine noble gas isotopic ratios, Scanning Electron Microscopy/Transmission
Electron Microscopy to examine magnetic/density separates and carbonaceous residue in search
for quantitative and qualitative trace material, and lastly but not least, Laser Inductively Coupled
Plasma-Mass Spectrometry to look for higher than average concentrations of Platinum Group
Elements. Both mass spectrometry techniques are reliable analytical methods in providing
precise elemental and isotopic compositions. Furthermore, Electron Microscopy serves as a
good technique for extraterrestrial particle investigation because it provides quantitative and
qualitative data required for relative trace metal concentrations, elemental ratios and
morphological components.
Procedures
The methods for the isolation of magnetic/density separates in order to extract the
magnetic microspherules and other metallic particles were as followed:
1) Solid bulk sediments were weighed out and placed into a beaker with deionized water; the
beaker was then placed in a sonicator allowing sediment particles to be sonicated with
heat for about 15 minutes.
2) After initial sonication a test tube containing a magnet was introduced into the original
beaker, the beaker with its contents was then allowed to sonicate for an additional 45
minutes with heat. [The sonicator agitates the molecules present in the sediment enabling
the magnetic constituents to cohesively attach to the magnet].
3) 20 mL of acetone was poured into a different small-sized beaker. The magnet-holding test
tube was then inserted into the acetone while the actual magnet itself was carefully
removed allowing the magnetic particles to fall off the test tube and settle into the beaker
with acetone.
4) Another magnet with an aluminum-covered top was inserted into the beaker by carefully
dipping the tip of the magnet into the meniscus of the acetone and placing the beaker into
the sonicator, allowing the magnetic particles to transfer from the acetone to the tip of the
Al-covered magnet.
5) SEM sample stubs were prepared by using double-sided carbon tape to transfer the
particles from the aluminum to the carbon tape. Prior to SEM analysis, samples were
sputter coated with gold in order to allow proper conductivity and mechanical stability.
Sample preparation for the noble gas mass-spectrometer was relatively straightforward. For the
magnetic separates, after step 4 (above), we simply rolled the aluminum that the metallic
particles were on into small Al balls that would fit into the furnace of the mass spec. Very
similarly for the bulk and acid treated sediment samples, we weighed them out on a scale and
rolled them into small aluminum balls that would fit into the furnace. The solid samples were
vaporized and any impurities were removed by using various getters and liquid nitrogen, the
isotopic ratios were measured according to published procedures.
The carbonaceous sediment from the End Pleistocene samples were prepared by performing acid
digestions with hydrofluoric acid to demineralize the sediment and remove all of the siliceous
content in order to leave only the organic carbonaceous residue. We prepared a couple of these
organic residue samples for the TEM by performing Size Exclusion Chromatography, in which
we separated the samples according to molecular weight, size and shape in order to purify and
filter out particulates. This was achieved by putting the sample into a .25% critical micelle
concentration SDS eluent with amphiphilic properties (similar to a detergent), then running it
through a stationary column matrix composed of a clean Control Pore Glass (CPG, with definite
pore sizes) by periodically flushing it with a 1% critical micelle concentration eluent (to make
sure particulates where undoubtedly wrapped in micelles) and finally capturing the filtered eluate
(containing the sample particles) into small vials. By predicting and controlling the order of
elution by using the total interaction volume and estimating the flow rate we were able to
separate and collect the particulates based on size as the particulates with different molecular
sizes filtered out at different rates with respect to average pore sizes present in the CPG column
matrix. Lastly, we prepared the chromatographed samples for the TEM by flushing them onto
carbon grids using clean pipettes. For sample preparation of the Laser ICP-MS, we eventually
prepared the sediment by placing them on glass slides and covering them with an epoxy polymer
material to safely adhere the samples to the glass, trying to clump and cluster as many chunky
grains together in order to prevent the laser from ablating right through the smaller grains. After
running the sediment samples in the Laser ICP-MS we obtained the data in intensity peaks and
then utilized a program called Geopro to convert the data into useful concentrations.
Results and Discussion
• Electron Microscopy
The Scanning Electron Microscopy results of magnetic fractions (micrographs, x-ray
spectra and weight composition charts) from some of the End Pleistocene samples and
Tunguska samples are included in the following pages; some extracted metallic grains do
provide strong potential ET tracers, others are included to compare information on the
common terrestrial counterparts and others are also included to illustrate the
contamination effects that can take place. We examined three carbon grids containing
organic carbonaceous residue from the acid digestions of some of the End Pleistocene
samples using the Transmission Electron Microscope, but we have decided to omit our
data on the TEM because we were not able to find any carbonaceous material of interest.
Nanodiamonds and nanotubes can be quite problematic to find.
The SEM micrograph below (along with its percentage composition chart) is from the
remarkable archaeological location of the Blackwater Draw site in New Mexico, a region of the
black mat with well-defined stratigraphic horizons. As we can see from the weight percentage
compositions, this magnetic grain has a massive enrichment of Platinum as well as high amounts
of Iron, Nickel and even some Iridium. Metallic grains such as this one are very strong indicators
of meteoritic material and impact ejecta, they have been used as reliable ET markers in past
extinction and impact events because they are extremely uncommon in the crustal earth.
The following magnetic particles are suspected spinel grains with anomalously higher
concentrations of either Nickel*, Magnesium, Chromium and with low or zero abundances of
Titanium. Spinel grains with higher than average concentrations of Fe-Cr-Ni are usually of
meteoritic origin; on the other hand, crustal spinels are usually Fe-Ti-O rich since meteorites are
usually not too enriched in Titanium and don’t readily incorporate it into impact mineral ejecta.
Figure 1 ET
Figure 2 ET
Figure 3 ET
Figure 4 ET
Figure 5 ET
For comparison, the following SEM micrographs are “background” grains of more than likely
terrestrial nature with abundances typically found in crustal environments.
Figure 1 crustal
Figure 2 crustal
Figure 3 crustal
Figure 4 crustal
A significant number of the magnetic grains we extracted from Tunguska had elevated
concentrations of Platinum Group Elements (mainly Platinum and Iridium), however we noticed
that they were also elevated in some conspicuous Rare Earth Elements, particularly Samarium,
Neodymium in conjunction with Cobalt. When we find speculative concentration peaks of these
metals and not significant peaks of the rest of the REEs, we must conclude that there was some
sort of contamination of the grains, especially since some of the magnets we utilized in the
extraction processes were Samarium/Cobalt and Neodymium/Iron magnets.
Figure 1 contamination
Figure 2 contamination
The following micrograph is a magnetic, iron rich, possible cosmic spherule from a sample
acquired in Tunguska, to its right is a typical iron-rich magnetic cosmic spherule retrieved from
sediment of the End Pleistocene.
The micrographs below are of possible Iron-Sulfide breccia melt particles resulting from violent
atmospheric/terrestrial collisions of ET material associated with impacts. In addition to x-ray
spectra analysis, micrographs of secondary electron detection (left) and backscatter electron
detection (right) are included. Our supplemental data from the Laser ICP-MS has suggested that
Fe-Ni-Sulfide minerals serve as important carrier phases for extraterrestrial siderophile Platinum
Group Elements.
The grains we were in search of generally had elements with higher atomic numbers, which emit
more backscattered electrons and appear brighter than the surrounding grains under the detector,
thus making it easier to pinpoint our grains of interest. In the micrograph(s) below (especially in
the backscatter one on the right) we can clearly see Pb particles retained within the Sulfur-rich
Iron Oxide grain, which could also be indicative of impact melt particles.
• Laser Inductively Coupled Plasma Mass Spectrometry
It is important to note that from the Laser ICP-MS data we can only deduce limited (yet valuable)
information due to limitations from the analytical techniques we performed, however, even
extremely low measurable concentrations of PGE’s can still be strong indicators of ET material.
We utilized the instrumentation at the ICP-MS facility located at the University of Massachusetts,
Boston with the help of our trusted colleagues. Lack of a suitable standard increased the error
estimate but still yielded useful PGE information as seen in Figures 1, 2 and 3 included later in
this report.
Firstly, using solely the raw data of peak intensities (counts), we noted that certain samples had
distinguishably higher counts of Iron, Nickel and PGE’s. This is true for the actual meteorite
samples plus the known boundary samples when compared to the sediments of suspected impact
layers. Another observation relates to the possible mineralogical fractions of the carrier phase of
PGE’s within the meteorites. Those same samples that had significantly higher counts of Ni-Fe-
PGEs also had higher counts of Sulfur but less counts of Silicon relative to the rest of the
samples, possibly entailing that the Platinum Group Elements were concentrated in the sulfide
mineral fractions of the samples.
Secondly, we actually were able to indeed quantify half of the PGEs (Pt, Pd and Rh) using the
declared concentrations of these three elements published in a previous peer-reviewed journal in
which they used the same standard that we ran, U.S. National Institute of Standards and
Technology Basalt Glass 612 (NIST 612)22
. Consequently, using a method known as “semi-
quantitative analysis” we calculated the relative concentrations of the remaining PGEs based on
the sensitivity of Platinum in the standard with respect to the Laser ICP-Mass Spectrometer.
Precision errors using this method are higher than using true quantitative analysis; however since
we correctly applied it to the same sample matrix we can expect surprisingly reasonable results
and thus accept it as a decent method for initial quantification. We can expect around a 5%
precision error for the elements we quantified from the standard and around 10-15% precision
error for the semi-quantified elements.
Our semi-quantitative analysis measurements were achieved by first calculating the sensitivity of
Platinum, which we calculated to be around 10,000counts/ppm. This was done by multiplying
the elemental concentration of Platinum in the standard which was retrieved from the
published journal that used the same standard times the abundance of the naturally occurring
isotope of Pt195
and dividing that value into the average of the measured counts for
Pt195
retrieved from the ICP-MS. We then assumed this same sensitivity for the ICP-
MS and applied it to the remaining PGE’s (Ir, Os and Ru), making sure to take the isotopic
abundances into account by multiplying this sensitivity by their respective isotopic abundances
and dividing that value into the average of the measured counts for each element, followed by
subtracting the counts measured in the blank for each of the elements/isotopes and finally getting
a rough estimate of the concentrations (in ppm).
Set up for the calculation for the sensitivity of Platinum:
Sensitivity of Pt = = = 10,000cts/ppm of Pt
193Ir = 0.626 10,000 = 6,300cts/ppm sensitivity for Ir
192Os = 0.41 10,000 = 4,100cts/ppm sensitivity for Os
102Ru = 0.316 10,000 = 3,200cts/ppm sensitivity for Ru
These sensitivity values were then divided into the average counts measured for each element in
the ICP-MS and subtracting the counts measured from the blank.
Finally, after performing the semi-quantitative analysis and obtaining relative concentrations for
all of the Platinum Group Elements we graphed the data using Sigmaplot program. The first
graph includes the relative concentrations of all the PGE’s plus Fe, Ni, Ti and Cr for all of the
samples. The second graph includes the relative concentrations of only the PGE’s in all of the
samples. The third graph includes the concentrations of Iridium versus the Nickel concentration
in all of the different samples, as we can presume that the origin of the extraterrestrial material is
from Ni-bearing meteorites.
The following are pics from the ICP-MS that we took as we blasted the grains with the laser.
• Noble Gas Mass Spectrometry
Our main idea for this section of analysis is to compare the measured isotopic ratios of noble
gases (3He/
4He and
20Ne/
22Ne) of our samples within the different fractions (magnetic,
carbonaceous and siliceous) to the average values associated with the constant flux of
interplanetary dust particles to the earth in order to speculate on the potential different
accumulation rates. The key point to discern is that variations present in the isotopic
compositions will help us get an idea of the accumulation rate of said gases, if values are
constant within the boundary then we can assume that the same flux was accreted during that
episode, and vice versa, if there are variations in the values then we can potentially assume that
the accumulation rate was unsteady. However, finding anomalous peak concentrations of these
ET gases does not necessarily mean that a major extraterrestrial body was the source, nothing
diagnostic can be deduced solely from the noble gas data, rather it serves as secondary
information which can help confirm the extraterrestrial implications. Furthermore, by comparing
the isotopic compositions between the magnetic, carbonaceous and siliceous fractions we can
deliberate on where the main carrier phase for the noble gases is concentrated. The following two
figures graph the 3He concentrations (versus depth) between the different fractions for samples
of three layers from the End Pleistocene and 3He/
4He ratios (versus depth) for the same three End
Pleistocene layers. Since we didn’t have rate values to plot against concentrations/ratios, we used
relative depth to account for time (from the sedimentation rate).
The noble gas data on 20
Ne/22
Ne and Tunguska has not shown much conclusive information, thus
no significant assumptions could be made at this time.
Our helium gas values for the most part have not shown any serious variation in isotopic values,
with the exception of one organic residue sample from the black mat of the Daisy Cave,
therefore we are assuming due to this low variation that the accumulation rates were steady for
each boundary. Once again with the exception of one anomalous outlier from the organic acid
residue, most values seemed to be concentrated within the magnetic fractions, suggesting that the
magnetic mineralogical carrier phase controls, to some extent, the retention and delivery of
extraterrestrial noble gases to earth. The only sample which had a 3He/
4He ratio close enough to
the extraterrestrial endmember value was the anomalous carbonaceous extraction, although we
can’t deduce that it was the direct result from an impact since it’s a single fluctuation, we can
deliberate on its potential carrier phase, perhaps fullerenes or silicon carbides which are believed
to be significant carrier vehicles of ET gases in carbonaceous material from outer space.
Conclusion
The analytical methods described in this project have served as legitimate tools for
extraterrestrial particle analysis; for our section of this much larger-scale investigation we have
explored the possibility of utilizing this research data to serve as possible concrete evidence to
prove that the suspected impact events were actually triggered by cosmic intrusions. On a similar
note, our supplemental geochemical and isotopic research data suggests that the main carrier
phases for extraterrestrial noble gases and platinum group elements are respectively concentrated
in the magnetic fractions and in the sulfide mineralogical fractions. The strongest indicators from
our resultant SEM data are the high-nickel iron oxide grains and suspected impact melt breccia
particles, which are generally considered acceptable evidence of ET material. On the other hand,
the TEM data we retrieved is rather inconclusive; we were not able to detect any carbonaceous
material of interest. Our noble gas data suggests accretion rates of the gases were generally
steady for the different layers. The Laser ICP-MS data shows that the meteorites and known
boundary samples had significantly higher concentrations of PGE’s (Iridium) and iron/nickel,
with also higher counts of Sulfur. More work on the samples from these events needs to be done
in assessing this long-term research project, but our described methods of analysis do indeed
serve as invaluable resources for the corresponding analysis.
References
1. LeCompte, Malcolm, Leroy Lucas, and Devina Hughes. “Younger Dryas Impact Study”.
Report
2. Kring, David A. “Impact Events and their Effect on the Origin, Evolution, and
Distribution of Life.” The Geological Society of America. 10, (2000).
3. Alley, R. B. "The Younger Dryas cold interval as viewed from central Greenland."
Quaternary Science Reviews 19 (200): 213-26.
4. Firestone, Rick, Allen West, Ted Bunch, James Wittke, and Luann Becker. “Research
into the Possibility of and End-Pleistocene Supernova and Related Impacts”.
5. Koch, Paul, Kathryn Hoppe, and David Webb. "ScienceDirect - Chemical Geology : The
isotopic ecology of late Pleistocene mammals in North America: Part 1. Florida."
ScienceDirect - Home. Elsevier Science B.V., 1998.
6. Firestone, Rick, Allen West, Ted Bunch, James Wittke, and Luann Becker. “Research
into the Possibility of and End-Pleistocene Supernova and Related Impacts”.
7. Lyne, J.E., Tauber, M. The “Tunguska Event”. Aerospace Engineering, University of
Tennessee. Aeronautics and Astronautics, Stanford University.
8. Vasilyev, N V. “The Tunguska Meteorite problem today.” PLANETARY AND
SPACE SCIENCE 46 (1998): 129-60. Print.
9. Norton, O. Richard. Rocks from Space: Meteorites and Meteorite Hunters. Missoula,
Mont.: Mountain Pub., 1998. p. 329-337. Print.
10. Palme, Herbert. Platinum-Group Elements in Cosmochemistry. Geochemistry &
Geophysics; Mineralogy 4.4 (2008): 233-38.
11. Cardiff University. School of Earth and Ocean Sciences. Platinum-Group Elements
(PGE) Geochemistry. Web Article.
<http://www.cardiff.ac.uk/earth/research/magmatic/areasprojects/geochemical/plat-
groupgeochem/index.html>.Platinum-Group Elements (PGE) Geochemistry.
12. Zanda, Brigitte, Monica Rotaru, and Roger H. Hewins. Meteorites Their Impact on
Science and History. Cambridge, UK: Cambridge UP, 2001. p.14 Print.
13. Lal, D. Jull, A.J. On the fluxes and fates of 3He accreted by the earth with
extraterrestrial particles. Earth and Planetary Science Letters 235 (2005) 375-390.
Science Direct Journal Article.
14. Zanda, Brigitte, Monica Rotaru, and Roger H. Hewins. Meteorites Their Impact on
Science and History. Cambridge, UK: Cambridge UP, 2001. p.44-45 Print.
15. Pierrard, O., Robin, E., et al. Extraterrestrial Ni-rich spinel in upper Eocene
sediments from Massignana, Italy. Geology, v.26, p.307-310. 1998
16. Darrah, T.H. Poreda, R.J. Noble Gas and Mineralogical Tracers of Interplanetary Dust
Particles and Impact Debris in a Central Pacific Sediment Core. American
Geophysical Union. 2005. Abstract #U33A-0004
17. Brownlee, D. "The elemental composition of stony cosmic spherules." Meteoritics and
Planetary Science. 32 (1997): 157-76.
18. Elekes, Z. et. al. Magnetic Spherules: Cosmic dust or markers of a meteoritic impact?
Elsevier Science B.V. 2001. p. 557-562. Article
19. Norton, O. Richard. Rocks from Space: Meteorites and Meteorite Hunters. Missoula,
Mont.: Mountain Pub., 1998. p. 97-100. Print.
20. French, Bevan M. Smithsonian Institution. Traces of Catastrophe: A Handbook of Shock-
Metamorphic Effects in Terrestrial Meteorite Impact Structures. Chapter 7: pg 97-
110. Lunar and Planetary Institute. 1998.
21. Kennett, J.D., Kennett, P.J., West, A, et al. Shock synthesized hexagonal diamonds in
Younger Dryas boundary sediments. National Academy of Sciences. 2009. Article
22. Sylvester, J.P., Eggins, M.S. Analysis of Re, Au, Pd, Pt and Rh in NIST Glass
Certified Reference Materials and Natural Basalt Glasses by Laser Ablation ICP-MS.
Geostandards and Newsletter- The Journal of Geostandards and Geoanalysis. Volume: 21
Issue: 2 Pages: 215-229. December, 1997
Acknowledgments
I would like to express my sincere gratitude to: Dr Robert J Poreda for the support and
opportunity to work on this project, Amanda Carey and Ann Dunlea for their assistance in the
laboratory, Dr Tom Darrah (and colleagues) for their guidance regarding the ICP-MS and
project-related work, Brian McIntyre for his expertise and training with the SEM/TEM, Dr Asish
R Basu and the rest of EES Departmental faculty for making this subject matter so interesting.