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

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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.