Journal of Creation 28(3):99–105, December 2014
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Precambrian impacts and the Genesis Flood
Only 182 impacts have been ‘confirmed’ on the earth. This number may be very low for two reasons. First, numerous impact craters are observed on the moon and other inner solar system bodies. Second, terrestrial impacts have been significantly modified by erosion and the emplacement of lava flows and thick sedimentary cover. The large Vredefort and Sudbury impact structures illustrate the extent of this alteration. Based on this evidence, other impact features may be difficult to identify. Other factors hindering the confirmation of past impacts, especially in the Precambrian, include overly stringent requirements for impacts, thick Phanerozoic cover, and the fact that until recent decades few geologists have been looking for impacts. Indirect evidence for other impacts, especially during the Precambrian, include cratonic basins, other circular or arc-shaped features, impact spherule layers, and other subtle geological and geochemical features. Thousands of impacts may have occurred during the Precambrian. It is likely that many Precambrian sedimentary rocks are Flood deposits, such as black shale, quartz arenite, phosphate-rich rocks, or those with diagnostic fossil traces, such as raindrop imprints. This suggests that many Precambrian impacts occurred during the Flood. These may have contributed to the energy needed to start and sustain the Genesis Flood.
Some creation scientists believe Precambrian sedimentary rocks are from the Flood, while others believe they are pre-Flood. The latter group also believes that the pre-Flood/ Flood boundary is at or slightly below the Precambrian/Cambrian boundary1,2 (assuming the geological column for sake of discussion). If the Precambrian is pre-Flood, where does it fit into biblical Earth history? The pre-Flood world is commonly seen as a generally benign geological period,3 which I agree with. So, the Precambrian is believed to be mostly a record of Creation Week.3,4
I have previously argued for a large number of unidentified terrestrial impacts, based on the size/frequency diagram of moon craters as well as other inner solar system bodies that have not been resurfaced. Based on that analysis, more than 36,000 impacts producing craters greater than 30 km (some very large) could have struck Earth during its history.5 Spencer updated this number to 58,000 based on newer data from the Lunar Reconnaissance Orbiter, and discussed that a crater-size cutoff of 30 km would eliminate most secondary craters caused by ejecta from large impacts.6 These data suggest that the solar system intersected a homogenous distribution of impactors in the past, assuming all impacts occurred about the same time.
However 58,000 impacts would have devastated Earth. Since it does not appear to have suffered that extent of damage, the number of impacts must have been fewer on Earth. Possibly some occurred during Creation Week,7 but I will focus on those likely to have occurred during the Genesis Flood. Very few impacts have been confirmed, relative to the numbers expected from the extraterrestrial evidence. One reason might be the overly stringent requirements to confirm impacts, which would have resulted in scientists having overlooked the vast majority of impacts. If that is the case, then much looser criteria must be found. To help define these, I examined the geological work expended by impacts, generally within the first hour.8 One significant result was that impact craters greater than 300 km in diameter create circular basins, without central uplifts. So we should not expect to find central uplifts when looking for large craters.
This paper will provide evidence for many more impacts than have been confirmed, especially Precambrian impacts. Furthermore, I will show that these Precambrian impacts likely occurred during the Flood, based on similar rocks and features in both the Precambrian and the Phanerozoic.9 This would indicate that the pre-Flood/Flood boundary is much lower than at or near the Precambrian/Cambrian boundary.
The RATE project and Catastrophic Plate Tectonics (CPT) propose the pre-Flood/Flood boundary is at or near the Precambrian/Cambrian boundary. If that aspect of RATE and CPT is wrong, then that work may require modification.
Recognized Precambrian impacts
As of 2011, 182 impacts had been reported by scientists,10 with one or two impact sites continuing to be added each year. Of these, 44 are greater than 20 km. Some of these are disputed by some geologists.11,12 Phanerozoic rocks contain 155 impacts; Precambrian rocks contain only 27, or 15% of the reported total (table 1). About six of these are of moderate (30 km or more) size.11 These Precambrian impacts are spread rather evenly from 545 Ma (million years before the present) to 2.4 Ga (billion years before present), assuming the uniformitarian dating of both impacts and rocks are accurate. Twenty-seven is a small number compared to the moon and other inner solar system bodies. This may imply that more Precambrian impacts exist but have not been recognized. Since the Phanerozoic has been better explored, it is unlikely that a significant number of new structures will be discovered, especially those greater than 30 km in diameter. Geophysical exploration of the subsurface has added only a small number of buried craters.13 If the actual total number of impacts is much greater than 182, and if these additional structures have not yet been found, then the logical conclusion is that geologists have not been looking for the right features.
Many Precambrian rocks are deformed, highly modified by tectonics, volcanism, and metamorphism. They, along with any craters they might contain, have been modified by erosion and buried by sediments. I therefore suggest that many unrecognized impacts in the Precambrian do in fact exist, and have been disguised by subsequent geological activity. Some impacts may even be obscured by later impacts in the same location. We know that large impacts occurred in the Precambrian: the Vredefort in South Africa and the Sudbury in Ontario, Canada. Both were devastating and their recognition controversial for some time. Therefore, it would appear that the great majority of Precambrian impacts may be unrecognized for various reasons or the evidence for impacts destroyed.
The Vredefort impact
The Vredefort impact is believed to be about 2 Ga old with a final crater diameter of about 250–300 km, making it both the largest and one of the oldest known impact structures on Earth. There is some debate on its diameter (table 1). It caused a central uplift with upturned and overturned Precambrian sedimentary rocks (figure 1). Erosion, estimated to be 8–11 km,14 has removed the rim and the crater fill, leaving behind concentric rings of granite, gneiss, migmatite, greenstone, and mantle rocks.15,16 To complicate the recognition of the Vredefort structure as an impact, there has also been post-impact regional deformation.
The Sudbury impact
An extraterrestrial origin of the Sudbury impact was also controversial for many years. It is not circular, but elongated in a northeast-southwest direction (figure 2).8 The impact diameter is unknown but the final crater diameter is believed to be 250 km in diameter, although some have claimed it is only 150–200 km in diameter or less.
It is dated at about 1.8 Ga old17 and about 5 km of erosion is believed to have occurred over the impact area.14 The Sudbury structure is most likely to be a 3-km-thick differentiated impact melt sheet, thought to have taken approximately a million years to cool.18 The Sudbury structure has yielded world-class ore deposits. Some of the debris ejected from Sudbury is now believed to have been found 600 km away, north of Lake Superior.19
Likely reasons for not recognizing impacts
Although Vredefort and Sudbury are now recognized as impact structures, their erosion and deformation suggests that other Precambrian impact structures may similarly have been heavily altered or even eradicated by erosion. If so, this suggests that other Precambrian impact structures will only be found by looking for features that are more subtle.
However, the stringent requirements for confirmation of impacts used by secular scientists likely means that the identification of many of these features may be impeded, especially in a Flood model. French and Koeberl, in their summary of convincing evidence for impact craters, downplayed the significance of circular or arc-shaped features and suggested that the only positive evidence for impacts is shatter cones and planar deformation features (PDFs) in quartz or other crystals.20 However, they admit that these features would not be common. Furthermore, recognizing shatter cones in the field is quite difficult, and many may have been eroded. PDFs would have formed only near the centre of the impact and would have been absent in the annular zone because the impact pressures decrease rapidly from the point of impact outward:
“The extreme pressure and temperature conditions of shock metamorphism, and the resulting diagnostic shock-deformation effects, are produced only within a relatively small volume of target rock near the impact point.”21
Moreover, it is difficult to find planar deformation features in a marine environment. Such stringent requirements, for the Precambrian, would contribute to far fewer impacts than have been recognized. The restrictive requirements may have resulted in hundreds of unidentified impacts being missed, especially since even suspected impact structures do not meet these requirements.20 The criteria should instead cover a comprehensive range of evidence.22
French and Koeberl are also thinking in uniformitarian terms. They assume isolated impacts separated by millions of years, which would better preserve shatter cones and PDFs, although these features would degrade in ‘older’ impacts.
After all, the two largest recognized Precambrian impact features have been eroded 5–10 km. If, during the Flood, there was a meteorite storm that resulted in as many as some thousands of impacts in a matter of days, forces would have been in play that would have obscured many of the impact structures. Nearby impacts would have destroyed previous craters and erratic, strong currents would have rapidly eroded shatter cones, PDFs, and other impact features. Cumulative heat from many impacts would have caused more rapid crustal metamorphism and deformation. The only remaining evidence may be large arc-shaped features.
It will also be difficult to find many Precambrian impacts on other than eroded cratonic shields because Precambrian rocks are usually buried under Phanerozoic sediments.
Another reason for the under-identification of impact structures may be psychological. If one does not expect to see signs of impacts, one most likely will not see the evidence. Recent studies have shown that bias by scientists does occur. For example, sleep researcher William Dement and writer Christopher Vaughan said referring to scientific observations: “even when they are looking, people usually see only what they expect to find and they do not see what they assume for whatever reason could not exist”.23
Evidence for many more Precambrian impacts
A few scientists have pointed out that the official criteria for identifying impacts are too stringent, and that finding ancient impacts is still a relatively new facet of earth science.24,25 That is why a statistical extrapolation from other solar system bodies may be the best method of determining that many more impacts in both Precambrian and Phanerozoic rocks exist. Some of the more indirect evidence pointing to many more impacts follows.
The main feature formed by an impact is the crater. It stands to reason, then, that craters from large impacts may appear as crater- or saucer-shaped basins. Although basins can form from other causes, these other mechanisms would not often produce a circular basin. We would expect such features to be better preserved on stable continental cratons. Indeed, 600 cratonic basins exist which have an approximate saucer shape in three dimensions.26 Most of these basins are greater than 300 km in diameter. Most have no central uplift, but usually have thinned crust, an uplifted mantle, and are filled with relatively undeformed, thick sedimentary rocks. All these features would be expected from impacts with little or slow subsequent deformation after the first hour. Although uniformitarian scientists have developed several hypotheses attempting to explain cratonic basins, they have been unable to explain them, and hardly ever think of an impact mechanism.26
Besides confirmed impacts, researchers have come up with many more possible impact structures, such as the Mt Ashmore structural dome in the Timor Sea,27 the Morokweng structure in South Africa,28 the buried East Warburton basin in northeast South Australia,29 a 500-km-diameter structure off the coast of India, a 300-km-diameter structure off Columbia, and a 225-km-diameter structure off Cuba.30 These identifications are based on generally circular or arc-shaped features. Large-scale circular or arc-shaped features are special features that are difficult to explain by any other geological process, other than impacts.31 Corner et al. write:
“Old structures are often difficult to recognize and are deeply eroded, but may still show geophysical signatures … that indicate the existence of a regionally distinct structure—especially if such signatures show a significant degree of circularity.”32
Based mainly on circular or arc-shaped features, Pesonen concludes that there are 50 unconfirmed impacts in Scandinavia with the largest at about 400 km in diameter, which compares to 22 confirmed impacts.33 That is 2.5 times as many unconfirmed impact structures as confirmed. Wikipedia34 lists many unconfirmed impact structures, four of which are large and of Precambrian ‘age’ (table 2). A new impact crater estimated to be 100 km in diameter was recently found in West Greenland (table 2) and dated to around 3 billion years old.35 This suggested impact was based mainly on its circular structure detected by geophysical means; normal criteria used to identify most of the recognized impacts could not be applied. Consequently, this impact is controversial and unconfirmed.36,37
Precambrian impact spherules
Geologists have discovered significant indirect evidence of more Precambrian impacts in the form of spherule layers in sedimentary rocks. Twelve spherule layers have been identified in various Precambrian formations.38 Most occur in the Archean Barberton formation of the Kaapvaal Craton of Africa and in the Pilbara Craton rocks of Western Australia. The Archean is older than 2.5 Ga, older than the oldest recognized impact from table 1. One Archean spherule bed extends over 325 km.39 Impact ejecta and spherules have been claimed in several other Precambrian formations.40,41,42 The significance of the Archean spherule layers has been challenged in the past,43,44 but most believe they are the result of impacts, mainly because of elements that are similar to those found in meteorites.45,46,47,48,49
Based on spherule-layer thickness and extent (tens of kilometres), some scientists have estimated the size of the impactors as tens of kilometres in diameter, which would have yielded craters hundreds of kilometres across.49,50 Glikson and Allen believe they have discovered the evidence of three major impacts in the Barberton formation of South Africa and the Hamersley Group rocks of Western Australia.51 They believe they can even estimate the size of the impactors at about 46 km, 16 km, and 28 km in diameter. Alternatively, the spherule evidence could be from a large number of impactors.52
Other possible impact evidence
Additional, indirect evidence for Precambrian impacts in sedimentary rocks is controversial. Geochemists have suggested an impact origin for some metasedimentary rocks in Greenland based on tungsten isotope ratios.53 Iridium spikes and chromium isotope ratios reinforce the impact origin of three early Archean layers within the Barberton formation of South Africa.54
Uniformitarian geologist Andrew Glikson, among others, believes that a wide range of mysterious geological features in the Precambrian, such as greenstone belts, banded iron formations, and large igneous provinces, can potentially be explained by impacts, but the evidence at this time is speculative.25,35,39,55,56,57
In addition to the 27 confirmed Precambrian impact structures, hundreds of possible impact structures have been detected, especially in the Precambrian. Evidence for an impact origin is based on the morphology of cratonic basins, other circular and arc-shaped structures, spherule layers, and other more indirect geological and geochemical features. As previously stated, other impact structures may have been destroyed or buried by other impacts, tectonics, volcanism, erosion, and deposition. The numbers of these may be substantial. Therefore, the number of impacts, especially in the Precambrian, could be in the hundreds to possibly a few thousand.
A large number of Precambrian impacts started the Flood
Where do these potential impacts fit in biblical Earth history? Even a small number of Precambrian impacts— the Vredefort impact is 300 km in diameter—would have devastated a large portion of the earth. Hundreds of large impacts within a short time would probably destroy life on Earth. Thus, it does not seem reasonable to place an impact event during the Creation Week. Also, impact events of this magnitude seem inconsistent with the divine pronouncement that the creation was ‘very good’. During a panel discussion at the 2013 International Conference on Creationism, Austin suggested that crystal defects were created in the rocks during Creation Week, and he stated that this apparent imperfection would justify a Creation Week impact event. However, that seems a tenuous inference.
Most, if not all, Precambrian sedimentary rocks from the Flood
If Earth impacts did not occur during Creation Week, the most probable option is during the Flood. This implies a Flood origin for Precambrian sedimentary rocks. Froede and I provided evidence that the diagnostic criteria placing the beginning of the Flood at or near the Precambrian/Cambrian contact are equivocal, and that this boundary was instead much lower in the Precambrian, possibly as deep as the crystalline basement.58,59 I am also inclined to the opinion that God miraculously modulated the impacts on Earth during the Flood, but not on other solar system bodies.60 After all, God is intimately involved and sustains His creation. He began the Flood, ended the Flood, and sat as King over the Flood.61
Another reason for assigning Precambrian sedimentary rocks to the Flood is their similarity to Phanerozoic rocks. They are similar in lithology; including limestone, dolomite, salt, chert, and diamictite. Moreover, some unusual rock types occur in both Precambrian and Phanerozoic strata, such as organic-rich black shale, quartz arenite, and phosphaterich rocks. Raindrop imprints also occur as early as the late Archean.9,62 These suggest that most Precambrian sedimentary rocks are from the Flood, and therefore many, if not all, Precambrian impacts occurred during the Flood.
Early Flood impact model
An early Flood impact model is suggested (figure 3). Powerful Precambrian impacts probably initiated the Flood63 (figure 3b), creating thousands of craters across the earth that would have been quickly modified due to differences in rock type, temperature, viscosity, etc. The erosion caused by the resulting currents would have been tremendous. Deposition at this time would have been restricted to deep impact basins where turbulence and currents would have been less (figure 3c).
The remainder of the sediments would have been in suspension, often in water thousands of metres deep. This would explain why Precambrian sediments are found mostly in what were once deep basins. Some of these basins were uplifted and eroded by isostatic recovery, such as the Belt Basin of the northern Rocky Mountains.26
The turbulence and strong currents would have scoured a planation surface over large areas (figure 3c), such as the Great Unconformity and similar surfaces in the western United States. This erosional surface appears to be a worldwide surface.64 Impacts probably declined rapidly through the mid and late Flood, with a few after the Flood. As the density and frequency of impacts declined, water current strength declined too, until a time of sedimentation was initiated—the ‘Great Deposition’ (figure 3d).
Paleozoic and Mesozoic sedimentary rocks were deposited over large areas, with little evidence of erosion or deformation within and between sedimentary layers. The thickness of these layers reaches thousands of metres in places. The ‘Great Deformation’, with differential vertical tectonics, tilting, and erosion, occurred later in the Flood, during the Recessional Stage, mainly during the Cenozoic.
Sedimentary rocks from the Cambrian through the end of the Mesozoic show little internal deformation. The absence of rocks reflecting the higher energy levels of the Flood’s beginning is a reason to place the pre-Flood/Flood boundary lower in the Precambrian. It may be that the impact event of the early Flood lasted 40 days, since impacting probably caused the torrential rain,65 and therefore the Great Deposition may not have begun until Day 40.
References and notes
- Austin, S.A. and Wise, K.P., The pre-Flood/Flood boundary: as defined in Grand Canyon, Arizona and eastern Mojave Desert, California; in: Walsh, R.E. (Ed.), Proceedings of the third international conference on creationism, technical symposium sessions, Creation Science Fellowship, Pittsburgh, PA, pp. 37–47, 1994. Return to text.
- Wise, K.P. and Snelling, A.A., A note on the pre-Flood/Flood boundary in the Grand Canyon, Origins 58:7–29, 2005. Return to text.
- Snelling, A.A., Earth’s Catastrophic Past: Geology, Creation & the Flood, vols. 1 and 2, Institute for Creation Research, Dallas, TX, 2009. Return to text.
- Baumgardner, J., Do radioisotope methods yield trustworthy relative ages for the earth’s rocks?, J. Creation 26(3):68–75, 2012. Return to text.
- Oard, M.J., How many impact craters should there be on the earth?, J. Creation 23(3): 61–069, 2009. Return to text.
- Spencer, W., Impacts and Noah’s Flood—how many and other issues, J. Creation 27(1):85–89, 2013. Return to text.
- Faulkner, D., A biblically based cratering theory, J. Creation 13(1):100–104, 1999. Return to text.
- Oard, M.J., What do impacts accomplish in the first hour?, J. Creation 27(1): 90–98, 2013. Return to text.
- Oard, M.J., Can the relative timing of radioisotope dates by applied to biblical geology?, J. Creation 27(2):112–119, 2013. Return to text.
- Earth Impact Database, passc.net, accessed 2013. Return to text.
- Reimold, W.U., The impact crater bandwagon (some problems with the terrestrial impact cratering record), Meteoritics & Planetary Science 42(9):1467–1472, 2007. Return to text.
- McCall, G.J.H., Half a century of progress in research on terrestrial impact structures: a review, Earth-Science Reviews 92:99–116, 2009. Return to text.
- Pilkington, M. and Grieve, R.A.F., The geophysical signature of terrestrial impact craters, Reviews of Geophysics 30(2):161–181, 1992. Return to text.
- Senft, L.E. and Stewart, S.T., Dynamic fault weakening and the formation of large impact craters, Earth and Planetary Science Letters 287:471–482, 2009. Return to text.
- Tredoux, M., Hart, R.J., Carlson, R.W. and Shirey, S.B., Ultramafic rocks at the center of the Vredefort structure: further evidence for the crust on edge model, Geology 27:923–926, 1999. Return to text.
- Henkel, H. and Reimold, W.U., Integrated geophysical modelling of a giant, complex impact structure: anatomy of the Vredefort Structure, South Africa, Tectonophysics 287:1–20, 1998. Return to text.
- Milkereit, B., Artemeiva, N. and Ugalde, H., Fracturing, thermal evolution and geophysical signature of the crater floor of a large impact structure: the case of the Sudbury Structure, Canada; in: Gibson, R.L. and Reimold, W.U. (Eds.), Large Meteorite Impacts and planetary Evolution IV, GSA special paper 465, pp. 115–131, 2010. Return to text.
- Barton, P.J., Grieve, R.A.F., Morgan, J.V., Surendra, A.T., Vermeesch, P.M., Christeson, G.L,, Gulick, S.P.S. and Warner, M.R., Seismic images of Chicxulub impact melt sheet and comparison with the Sudbury structure; in: Gibson, R.L. and Reimold, W.U. (Eds.), Large Meteorite Impacts and planetary Evolution IV, GSA special paper 465, pp. 103–113, 2010. Return to text.
- Addison, W.D., Brumpton, G.R., Davis, D.W., Fralick, P.W. and Kissin, S.A., Debrisites from the Sudbury impact event in Ontario, north of Lake Superior, and a new age constraint: are they base surge deposits or tsunami deposits?; in: Gibson, R.L. and Reimold, W.U. (Eds.), Large Meteorite Impacts and planetary Evolution IV, GSA special paper 465, pp. 245–268, 2010. Return to text.
- French, B.M. and Koeberl, C., The convincing identification of terrestrial meteorite impact structures: what works, what doesn’t, and why, Earth-Science Reviews 98:123–170, 2010. Return to text.
- French and Koeberl, ref. 20, p. 142. Return to text.
- Glikson, A. and Uysal, I.T., Geophysical and structural criteria for the identification of buried impact structures, with reference to Australia, Earth-Science Reviews 125:114–122, 2013. Return to text.
- Dement, W.C. and Vaughan, C., The Promise of Sleep: A Pioneer in Sleep Medicine Explores the Vital Connection Between Health, Happiness, and a Good Night’s Sleep, A Dell Trade Paperback, New York, p. 34, 1999. Return to text.
- Glikson, A.Y., Asteroids and early Precambrian crustal evolution, Earth-Science Reviews 35:285–319, 1993. Return to text.
- Glikson, A.Y. and Vickers, J., Asteroid impact connections of crustal evolution, Australian J. Earth Sciences 57:79–95, 2010. Return to text.
- Oard, M.J., Large cratonic basins likely of impact origin, J. Creation 27(3):118–127, 2013. Return to text.
- Glikson, A.Y., Jablonski, D. and Westlake, S., Origin of the Mt Ashmore structural dome, west Bonaparte Basin, Timor Sea, Australian J. Earth Sciences 57:411–430, 2010. Return to text.
- Corner, B., Reimold, W.U., Brandt, D., and Koeberl, C., Morokweng impact structure, Northwest Province, South Africa: geophysical imaging and shock petrographic studies, Earth and Planetary Science Letters 146:351–364, 1997. Return to text.
- Glikson, A.Y., Uysal, I.T., Fitz Gerald, J.D. and Saygin, E., Geophysical anomalies and quartz microstructures, Eastern Warburton Basin, north-east Australia: tectonic or impact shock metamorphic origin? Tectonophysics 589:57–76, 2013. Return to text.
- Kutcherov, V.G. and Krayushkin, V.A., Deep-seated abiogenic origin of petroleum: from geological assessment to physical theory, Reviews of Geophysics 48:1–30, 2010. Return to text.
- Stewart, S.A., How will we recognize buried impact craters in terrestrial sedimentary basins?, Geology 31:929–932, 2003. Return to text.
- Corner et al., ref. 28, p. 352. Return to text.
- Personen, L.J., The impact cratering record of Fennoscandia, Earth, Moon, and Planets 72:377–393, 1996. Return to text.
- List of impact craters on Earth , en.wikipedia.org, accessed 2013. Return to text.
- Garde, A.A., McDonald, I., Dyck, B. and Keulen, N., Searching for giant, ancient impact structures on Earth: the Mesoarchaean Maniitsoq structure, West Greenland, Earth and Planetary Science Letters 337–338:197–210, 2012. Return to text.
- Wolf, U., Gibson, R.L. and Koeberl, C., Comment on “Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland” by Garde et al. [Earth Planet. Sci. Lett. 337–338:197–210, 2012], Earth and Planetary Science Letters 369–370:333–335, 2013. Return to text.
- Garde, A.A., McDonald, I. and Dyck, B., Reply on “Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland” by Garde et al. [Earth Planet. Sci. Lett. 337–338:197–210, 2012], Earth and Planetary Science Letters 369–370:336–343, 2013. Return to text.
- Johnson, B.C. and Melosh, H.J., Impact spherules as a record of an ancient heavy bombardment, Nature 485:75–77, 2012. Return to text.
- Glikson, A.Y., Field evidence of Eros-scale asteroids and impact-forcing of Precambrian geodynamic episodes, Kaapvaal (South Africa) and Pilbara (Western Australia) Cratons, Earth and Planetary Science Letters 267:558–570, 2008. Return to text.
- Amor, K., Hesselbo, S.P., Porcelli, D., Thackrey, S. and Parnell, J., A Precambrian proximal ejecta blanket from Scotland, Geology 36:303–306, 2008. Return to text.
- Gostin, V.A., Haines, P.W., Jenkins, R.J.F., Compston, W. and Williams, I.S., Impact ejecta horizon within Late Precambrian shales, Adelaide Geosyncline, South Australia, Science 233:198–200, 1986. Return to text.
- Williams, G.E., The Acraman impact structure: source of ejecta in late Precambrian shales, South Australia, Science 233:200–203, 1986. Return to text.
- Koeberl, C., Reimold, W.U. and Boer, R.H., Geochemistry and mineralogy of Early Archean spherule beds, Barberton Mountain Land, South Africa: evidence for origin by impact doubtful, Earth and Planetary Science Letters 119:441–452, 1993. Return to text.
- Hofmann, A., Reimold, W.U. and Koeberl, C., Archean spherule layer in the Barberton greenstone belt, South Africa: a discussion of problems related to the impact interpretation; in: Reimold, W.U. and Gibson, R.L. (Eds.), Processes on the early Earth, GSA Special Paper 405, Geological Society of America, Boulder, CO, pp. 33–56, 2006. Return to text.
- Rasmussen, B. and Koeberl, C., Iridium anomalies and shocked quartz in the Late Archean spherule layer form the Pilbara craton: new evidence for a major asteroid impact at 2.63 Ga, Geology 32(12):1029–1032, 2004. Return to text.
- Glikson, A., Asteroid impact ejecta units overlain by iron-rich sediments in 3.5–2.4 Ga terrains, Pilbara and Kaapvaal cratons: accidental or cause—effect relationships? Earth and Planetary Science Letters 246:149–160, 2006. Return to text.
- Glikson, A., Siderophile element patterns, PGE nuggets and vapour condensation effects in Ni-rich quench chromite-bearing microkrystite spherules, ~3.24 Ga S3 impact unit, Barberton greenstone belt, Kaapvaal Craton, South Africa, Earth and Planetary Science Letters 253:1–16, 2007. Return to text.
- Goderis, S., Simonson, B.M., McDonald, Hassler, S.W., Izmer, A., Belza, J., Terryn, H., Vanhaecke, F. and Claeys, P., Ni-rich spinals and platinum group element nuggets condensed from a late Archaean impact vapour cloud, Earth and Planetary Science Letters 376:87–98, 2013. Return to text.
- Lowe, D.R., Crustal fracturing anc chert dike formation triggered by large meteorite impacts, ca. 3.260 Ga, Barberton greenstone belt, South Africa, GSA Bulletin 5/6:894–912, 2013. Return to text.
- Byerly, G.R., Lowe, D.R., Wooden, J.L. and Xie, X., An Archean impact layer from the Pilbara and Kaapvaal cratons, Science 297:1325–1327, 2002. Return to text.
- Glikson, A. and Allen, C., Iridium anomalies and fractionated siderophile element patterns in impact ejecta, Brockman Iron Formation, Hamersley Basin, Western Australia: evidence for a major asteroid impact in somatic crustal regions of the Early Proterozoic earth, Earth and planetary Science Letters 220:247–264, 2004. Return to text.
- Glikson, A.Y., Allen, C. and Vickers, J., Multiple 3.47-Ga-old asteroid impact fallout units, Pilbara Craton, Western Australia, Earth and Planetary Science Letters 221:383–396, 2004. Return to text.
- Schoenberg, R., Kamber, B.S., Collerson, K.D. and Moorbath, S., Tungsten isotope evidence from ~3.8-Gyr metamorphosed sediments for early meteorite bombardment on the Earth, Nature 418:403–405, 2002. Return to text.
- Kyte, F.T., Shukolyukov, A., Lugmair, G.W., Lowe, D.R. and Byerly, G.R., Early Archean spherule beds: chromium isotopes confirm origin through multiple impacts of projectiles of carbonaceous chondrite type, Geology 31:283–286, 2003. Return to text.
- Glikson, A.Y., The astronomical connection of terrestrial evolution: crustal effects of post-3.8 Ga mega-impact clusters and evidence for major 3.2±-.1 Ga bombardment of the Earth—Moon system, J. Geodynamics 32:205–229, 2001. Return to text.
- Glikson, A.Y., Asteroids and early Precambrian crustal evolution, Earth-Science Reviews 35:285–319, 1993. Return to text.
- Macdonald, F.A., Bunting, J.A. and Cina, S.E., Yarrabubba—a large, deeply eroded impact structure in the Yilgarn Craton, Western Australia, Earth and Planetary Science Letters 213:235–247, 2003. Return to text.
- Oard, M. and Froede Jr., C., Where is the pre-Flood/Flood boundary?, Creation Research Society Quarterly 45(1):24–39, 2008. Return to text.
- Froede Jr, C.R. and Oard, M.J., Defining the pre-Flood/Flood boundary within the Grand Canyon: were all the pre-Flood sediments scoured down to basement during the Flood?, Creation Matters 12(3):3–4, 2007. Return to text.
- Oard, M.J., Michael Oard replies, J. Creation 24(1):48–49, 2010. Return to text.
- Oard, M.J., An impact Flood submodel—dealing with issues, J. Creation 26(2):73–81, 2012. Return to text.
- Oard, M.J., Raindrop imprints and the location of the pre-Flood/Flood boundary, J. Creation 27(2):7–8, 2013. Return to text.
- The question of how impacts initiated the Flood is outside the scope of this paper. Return to text.
- Oard, M.J., The meaning of the Great Unconformity and Sauk Megasequence, J. Creation 28(1):12–15, 2014. Return to text.
- Spencer, W.R., Geophysical effects of impacts during the Genesis Flood; in: Walsh, R.E. (Ed.), Proceedings of the Fourth International Conference on Creationism, technical symposium sessions, Creation Science Fellowship, Pittsburgh, PA, pp. 567–579, 1998. Return to text.
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