Size of the craters

…Koeberl states that the earth would have undergone impact events an order of magnitude larger than the moon and experienced many more such events.³ There would be hundreds of objects with sizes similar to those that created the Imbrium and Orientale craters that must have struck Earth during the basin-forming era. Ryder also says that the earth would have undergone events an order of magnitude larger than the moon with many more impacts.²⁹ Melosh suggests that there should be 100 impact structures with diameters greater than 1,000 km on Earth, based on the moon.²¹ 

Samec calculates that the moon was hit by an asteroid swarm equivalent to a 70 km diameter solid asteroid.^36,37 He divides this asteroid up into 23 equal chunks with sizes averaging 24.5 km in diameter, equal to the number of large impact basins, and calculates a crater average diameter of 850 km, which is close to the average of those large impact basins on the moon. Samec uses an average distribution, but in reality the sizes of the impactors would vary significantly around the mean diameter of 24.5 km resulting in a variety of crater diameters as observed on the moon. Using the moon as an analog and the average crater size, he obtains 310 collisions for the earth, each causing 740 km diameter craters.

However, he used the physical cross sectional area and not the gravitational cross section area. So, these 310 collisions would have to be multiplied by 1.4 to obtain 434 huge impacts greater than 740 km. The upshot of Samec’s and other’s research is that the earth should have been bombarded with several hundred impacts producing craters larger than 740 km in diameter.

Kring and Cohen believe that the LHB was by asteroids from a single dynamic reservoir.4 They estimate the earth was hit by 13 to 500 times more mass than the moon, depending upon size distribution among impactors. Just using the lower number of mass, they conclude that the earth had 22,000 impact craters during the LHB greater than or equal to 20 km, including about 40 impact basins about 1,000 km in diameter, and several with diameters of about 5,000 km! But scaling to Mars would predict 6,400 craters greater than or equal to 20 km, but there are 9,278 craters of those dimensions.

Shane Torgerson via Wikimedia

So, Kring and Cohen’s numbers are probably low for the earth. There is the question of how Kring and Cohen came up with the result that the earth should have a few impact basins 5,000 km in diameter. They obviously extrapolated the SFD for the moon to the earth. The largest impact on the moon is South Pole-Aitken with a diameter of about 2,500 km (figure 6). Using more sophisticated analysis, Mars may have 20 craters larger than 1,000 km with five 2,639 to 3380 km in diameter.¹⁰ Since Mars has a smaller gravitational cross section than the earth, the earth should have significantly larger diameter craters than Mars. So there is justification for an extrapolation to the earth from Mars and the moon for a few large craters around 4,000 km in diameter or more, so a 5,000-km diameter crater is not too outlandish.

So, it is safe to conclude that the earth should have 36,000 impact craters with about 100 over 1,000 km, and a few with diameters of 4,000 to 5,000 km. Such a great bombardment would pulverize a larger portion of the earth surface.

When did Earth impacts occur?

When could such a bombardment occur in biblical Earth history? It is likely that very few impacts occurred after the Flood (assuming the Flood/post-Flood boundary is in the very late Cenozoic), since there are only a few pristine impact craters, such as Meteor Crater (figure 3) that are clearly post-Flood.³⁸ If even a small fraction of the 36,000 impacts occurred after the Flood (as well as before the Flood), all biology would have been wiped out.

In regard to possible impacts before the Flood, I accept Spencer’s analysis³⁵ that the solar system was created stable with no impact structures. This seems logical to me, since everything was created very good, and meteorite bombardments do not seem to be very good phenomena, especially if there were organisms living on the earth at the time. So, it does not seem likely that there were two bombardments, one at the Creation or the Fall and a second during the Flood as advocated by Danny Faulkner.³⁹ The moon was created on Day 4, so that any moon bombardment afterwards could hardly have missed the earth, in which case all or practically all newly-created organisms would have been wiped out. A bombardment at the Fall would also be devastating.

So, all these 36,000 impacts very likely occurred during the Flood, which I have maintained for a long time:

“Impact craters are common on the inner planets and our moon, which implies that the earth probably was bombarded at some time in the past. We find very few impact craters on the surface of the earth, indicating that catastrophic meteorite bombardment would have occurred either before the Flood or during the Flood. If the pre-Flood earth was a time of climatic and geographic stability, it is doubtful that the meteorite bombardment was before the Flood. The only possibility left is that the event occurred during the Genesis Flood.”⁴⁰

All the solar system bodies were likely struck by the same event, as indicated by similar crater SFD statistics on the inner solar system, except for Venus. However, Venus likely has many more visible impacts than astronomers believe.¹² 

Based on the relative dating of the moon, it looks like most of the very large impacts struck right away on the near side of the moon (figure 7) with a rapid tailing off of impacts. The far side has only a few medium sized basins. Because of the 27.3-day rotation of the moon and the maria being spread horizontally over 45% of the lunar surface, mainly on the near side, Samec concludes that the large impacts on the moon occurred over a period within 12 days.³⁷ 

He prefers a much shorter time frame, probably over a span of a few days. These large impacts could be associated with the late LHB. (The LHB is controversial among astronomers, but this dispute does not concern creationists since the LHB depends upon whether there was an Early Heavy Bombardment that formed the moon and caused the magma ocean, both of which there is no evidence for and depend upon evolutionary speculation.)

Since the mare basalts likely flowed soon after the impacts and have much fewer impacts than the lunar highlands, the number of impacts must have decreased rapidly after the initial large barrage. Also, the radiometric dates between the LHB and the mare basalt show that the radiometric dates are highly exaggerated. Remember that relative dating, which seems reasonable, only gives the sequence of events and not the absolute time or the real time between events. So, it looks like the larger impacts struck at the very beginning of the Flood in a matter of a few days, or even less, and decreased rapidly afterwards with only a few small impacts after the Flood.^35,41,42 We can also conclude from the near side moon impacts that the largest impactors came from one direction.

Impacts likely caused the Flood

So many impacts, some huge, would have provided a prodigious amount of energy to the earth. Such an amount of energy, especially delivered quickly and not over millions and billions of years, would have many effects on the earth. It is beyond the scope of this paper to estimate the effects of this energy, but regardless the amount would have been devastating. Since the Flood requires energy, meteorite impacts could easily provide the necessary energy to start and maintain the Flood. A number of creationists have suggested impacts as the source of this energy, regardless of whether catastrophic plate tectonics occurred later or not.^{35,36,37,39,41,42,43,44,45,46,47} 

Where are the impact craters on Earth? If the earth had 36,000 impact craters greater than 30 km with more than 100 greater than 1,000 km in diameter and a few up to 4,000 to 5,000 km, then where is the evidence for all these craters? Only about 170 impact craters and structures, some buried, are claimed for the earth,³ mostly in the Paleozoic.⁴¹ The answer is that the tremendous tectonics, erosion, and deposition during the Flood would have altered or destroyed the vast majority of these craters.

The Paleozoic and Mesozoic sediments are mostly large sheets of strata that cover large areas, while the Cenozoic and Precambrian is more restricted, assuming the uniformitarian geological column. Since geologists have studied much of the sedimentary rocks either by direct observation or by seismic methods, very little evidence for impact structures has emerged.

So, it is not likely that a significant proportion of the 36,000 impacts will be found within sedimentary rocks. Therefore, it seems apparent that such a large amount of impacts will mainly have affected the Precambrian igneous rocks, which likely was the pre-Flood upper crust.

There are only 3 or 4 examples of Precambrian impact craters or structures.⁴¹ Because of all the Flood devastation, the evidence for a huge amount of impacts in the Precambrian likely would be found if we look for more subtle indicators. Regardless, it seems evident that most of the impacts will be associated with the Precambrian.

So, it looks like the beginning of the Flood would correspond to the Precambrian of the uniformitarian geological column.⁴⁸ Much of the Precambrian and Phanerozoic sedimentary rocks likely are the deposits churned up by all the impacts and laid down after the initial chaos of the Flood mechanism.

Such a scenario goes along with two general diastrophic cycles recognized by Thom over the western United States.⁴⁹ He recognized an Early Precambrian diastrophic time of basin subsidence and sedimentation, orogenic compression and folding with volcanism, regional vertical uplift, and planation of mountain system. Such energetic effects could be the result of the initial Flood impacts, since impacts would cause basins with mountains formed along the rims of the basins. The basin would then fill with sediments, and of course much volcanism would be expected with the impacts. The impact uplifted rims and isostatically uplifted basins would supply vertical tectonics. Very strong currents in water caused by the impacts could easily plane rocks.

The second diastrophic cycle is continuing today, according to Thom, but started with the deposition of thick Precambrian sediments and continued with the Paleozoic and Mesozoic sedimentation. Then uplift has ensued with orogenic compression and folding with volcanism and planation, mainly in the late Mesozoic and Cenozoic.

Such a general sequence would correspond to the stages and phases of the Flood.^50,51 in which the first diastrophism was caused by impacts, the mechanism of the Flood, followed by the deposition of all the debris churned up by that devastation in the later part of the Flooding Stage. The second diastrophism would correspond to the Retreating Stage with uplift and volcanism as the Floodwater retreated off the continents.

Knowing that the Flood would greatly modify the craters, we need to look for more indirect, subtle evidence for these impacts in Precambrian igneous and metamorphic rocks. One example of such subtle evidence could be ophiolite belts where mantle rocks were overthrust onto other rocks, especially if the ophiolite belt has a semicircular shape. The Oman ophiolite would fit an impact scenario.⁵² Another subtle piece of evidence probably is the ultrahigh-pressure minerals and microdiamonds now found in mountains areas all over the world.⁵³ Ultrahigh-pressure minerals and microdiamonds can be formed by impacts. Otherwise the alternative is to rapidly push continental rocks well below 100 km and then rapidly exhume them, presenting a tectonic conundrum, especially for uniformitarians.

Summary and discussion

Mercury, Mars, and the moon have similar cratering histories.³³ The moon is used as the standard by which to estimate the number of craters that bombarded the earth. The number of craters greater than 30 km calculated for the moon is about 1,900, which is a minimum because of the problem of saturation. In scaling from the moon to the earth, the difference in crater sizes must be taken into account. The earth’s stronger gravity will result in a transient crater only 2/3rds the size of one on the moon with the same velocity and size of impactor. However, the greater gravity of the earth will result in the crater becoming larger because of gravitational mass movement and slumping. So, the final crater size on the earth will be close to that on the moon.

Scaling the number of impacts from the moon to the earth is based mainly on the greater gravitational cross section of the earth. As a result, there should have been 36,000 craters greater than 30 km on the earth. Of these, by an extrapolation of the size-frequency distribution, about 100 craters greater than 1,000 km in diameter and a few up to 4,000 to 5,000 km in diameter should have occurred on Earth.

Since such a bombardment did not occur after the Flood because there are very few pristine craters, the bombardment must have been pre-Flood or during the Flood. But if pre-Flood, the devastation would have wiped out all biology on Earth. So, the only logical conclusion is that all these impacts occurred during the Flood. Based on the moon, it seems that the largest impacts must have occurred very early in the Flood, tailing off during the rest of the Flood with only a few post-Flood impacts. Such a bombardment would have enough energy to initiate the Flood, although many details need to be worked out. The evidence for such an impact bombardment very likely first affected the pre- Flood crystalline rocks and suggests that the Precambrian is early Flood.

The number of impacts that occurred during the Flood seems sound. However, there are many questions and additional areas of research beyond the scope of this article. Although impacts into the pre-Flood oceans would blast up plenty of water into the atmosphere and beyond for subsequent heavy rain,⁵⁴ one issue is how such a bombardment caused the Flood. Another issue is whether the amount of energy is too devastating.

Of course, much subtle geological evidence should point to impacts, but this evidence, almost always interpreted within a non-impact uniformitarian framework, needs to be worked out within an impact model. It is to be expected that God protected the ark from asteroid impacts, but why does the Bible not directly mention impacts? Regardless, the number of impacts to bombard the earth, the objective of this paper, is the first step in developing a new model of the Flood, based on impacts.