In a previous article titled "Did Earth 'Steal' Martian Water?", I mentioned that a close encounter between Mars and Earth occurred ca. 12,500 BP (10,500 BC). Mars was knocked close to Earth by Venus which, at the time, was a cometary body. The past cometary nature of Venus has been amply theorized by Velikovsky and demonstrated by recent observations.

I en tidligere artikel, Stjal Jorden Marsvandet ("Did Earth 'Steal' Martian Water?)? Nævnte jeg, at der opstod et tæt møde mellem Mars og Jorden ca. 12.500 BP (10.500 f.Kr.). Mars blev skubbet tæt på Jorden af ​​Venus, som på det tidspunkt var et kometagtig klode. Den tidligere kometagtige karakter af Venus er blevet rigeligt teoretiseret af Velikovsky og demonstreret ved nylige observationer.

Ovennævnte artikel efterlod imidlertid en masse spørgsmål vedrørende Venus.

Hvad skete der med Venus, efter at den interagerede med Mars? Hvor lang tid tog det for Venus at erhverve sin nuværende cirkulære, planetariske bane? Havde den kometære Venus andre interaktioner med planeten Jorden? Hvor mange passeringer foretog Venus, før den fik en stabil bane? Hvad var datoerne for disse pas? Hvad var deres virkning?

Venus cometary tail
© ESA
Solen til venstre i billedet og Venus med en kometagtig hale i midten til højre


Kommentar: Delvist oversat fra The Seven Destructive Earth Passes of Comet Venus


Ca. 12,500 BP cometary Venus was inside the solar system and knocked Mars towards Earth. Nowadays Venus is not a comet; it is a planet with a stable circular orbit.

Venus being a planet is attested as far back as Mesopotamia (ca. 4,500 BP), which likely means that the transformation of Venus from comet to a planet occurred between 12,500 BP and 4,500 BP.

This transformation involved an orbital change, a transition from a long-duration highly elliptical orbit to a short-duration circular orbit. It is the progressive capture of a comet by the Sun that transformed it into a stable planet, a process which probably involved several passes, with a shorter and shorter time gap between 12,500 and 4,500 BP.

Asteroid transition from a elliptical to a circular orbit
© Tufts University
Asteroid transition from a elliptical to a circular orbit
In order to determine when this progressive capture of Venus occurred, we must first identify the Venus markers, i.e. what kind of earthly parameters would have been modified by a fly-by of cometary Venus?

Venus Markers


There is no known Venusian meteorite found on Earth, which suggests a limited transfer of solid material, if any. This is due to the fact that escape velocity on Venus is high (10.4 km/s VS 6.5 km/s on Mars) and elevated drag in the dense Venusian atmosphere would prevent anything reaching escape velocity and leaving the planet.

Discarding rocks, we will focus on more volatile materials like the gases in Venus' atmosphere and tail that exist in higher concentrations than they do on Earth.

Thus, a close encounter with Venus might be identified by a sharp rise in terrestrial samples (pit cores, ice cores...) of those Venus-abundant gases.

The graph below shows the concentration of gases in Venus and Earth's atmospheres:
Venus atmosphere VS. Earth atmosphere
© Rakhecha et al., 2009
Venus atmosphere VS. Earth atmosphere
As you can see, two gases stand out as notably more concentrated on Venus than on Earth. These are carbon dioxide (CO2 - as indicated by the red bars) and sulfur dioxide (SO2 - as indicated by the green bars). Notice that the scale is logarithmic, therefore a one gradation increase in the chart corresponds to a tenfold increase in terms of gas concentration.

CO2 constitutes 96.5% of Venus' atmosphere and only about 400 ppm (0.04%) of Earth's atmosphere, which is a 2,500-fold difference. As far as sulfur dioxide is concerned, Venus' atmosphere contains 186 ppm while Earth's atmosphere only contains about 10 ppb (part per billion), which is a 20,000-fold difference.

Beside those "common" gases, there is also deuterium. Its abundance on Earth is about 100 ppm (0.01%), while its abundance on Venus is about 100 times higher.

In addition to those three gases, there are hydrocarbon compounds (including one of its simplest forms - methane). Velikovsky hypothesized the presence of hydrocarbons in Venus' atmosphere as early as the 1960s, as detailed in the second chapter of Worlds in Collision - titled 'Naphtha'.

The idea that comets in general, and Venus in particular, contain hydrocarbons was ridiculed at the time by Carl Sagan et al. Three decades later, direct observations of Venus' high atmosphere proved Velikovsky right:
"Donahue and his collaborators... characterize the finding [of methane in Venus] as so surprising that they were loathe to publish them..."

The researchers base their unlikely conclusion [that the methane is of volcanic origin] on the abundance and composition of methane detected by a mass spectrometer aboard the Pioneer-Venus Probe. Scientists had known for years that the spectrometer had recorded a sharp rise in methane, beginning at about 14 kilometers above the surface of Venus, during the probe's descent.

But for nearly a decade, Donahue and his co-workers believed the surge merely reflected methane placed in the spectrometer on Earth in order to calibrate the instrument, not activity on Venus...

"We concluded that the methane sampled was a primeval methane freshly vented from the planet's interior," says Donahue... he estimates that a volcanic eruption spewing out the amount of methane found by the Pioneer-Venus would occur only about once every 100 million years.

Moreover, it appears that the probe passed through the [methane] plume near the top of the atmosphere, where winds would have stretched the vented methane over a wide area, as well as closer to the surface of the planet...

"It is embarrassing to invoke such a wildly unlikely event as a chance encounter between the entry probe and a rare and geographically confined methane plume, but so far we have eliminated all other plausible explanations," Donahue added.

- Science News, (September 12, 1992), page 172
Despite Velikovsky being proven correct, the mainstream scientific dogma that "there is no methane in Venus' atmosphere" and "therefore Velikovsky is wrong and uniformitarianism prevails," scientists had to invoke an unsubstantiated and extremely unlikely cause to explain the methane in Venus' atmosphere. As Charles Ginenthal put it:
"To explain the large amount of methane found in the Venus atmosphere the scientist said that the methane had to have come from an extremely rare volcanic eruption.

The one explanation omitted by Donahue is that Venus has a good deal of methane in its atmosphere, just as Velikovsky predicted. Scientists would rather suggest a wildly improbable concept to explain the methane found than give consideration to Velikovsky's prediction.

While scientists like Sagan will call Velikovsky's theory extremely improbable, they will propose that it is probable that Pioneer-Venus just happened to come down on Venus to experience a unique event that happens once every hundred million years."

- Charles Ginenthal, Carl Sagan and Immanuel Velikovsky
The presence of hydrocarbons around Venus was suggested by Velikovsky because its 2 million mile-long tail does contain carbon, as detected in the late 1970s by the SOHO probe, and hydrogen ions, the two constituents of hydrocarbon. For example, methane, one of the simplest forms of hydrocarbon, is made of one atom of carbon and four atoms of hydrogen, hence its formula: CH4.

Up to now we have identified four gases (SO2, CO2, D, CH4) that are substantially more abundant in Venus' atmosphere than in Earth's atmosphere. A close encounter between the two celestial bodies should have left concentration spikes for those gases in earthly records.

Picture of Venus thick atmosphere and scortched surface taken by Russian probe Venera
© USSR Academy of Sciences
Picture of Venus thick atmosphere and scortched surface taken by Russian probe Venera in 1981
Besides the gaseous spikes, cometary Venus should have left the typical signature of cometary encounters: increased dust due to crossing the cometary tail, the impact and/or overhead explosions of cometary fragments, and the induced volcanism/seismicity as described in my article titled 'Volcanoes, Earthquakes And The 3,600 Year Comet Cycle'.

This increase in atmospheric dust typically induces larger cloud cover (dust acts as a nucleation agent for cloud formation). In turn, the increased cloud cover leads to increased rainfall and a temperature drop.

In total then, we have identified seven potential markers of a Venus encounter:

- Sulfur dioxide (SO2)
- Carbon dioxide (CO2)
- Deuterium (D)
- Methane (CH4)
- Increased dust
- Increased precipitation
- Temperature drops

The diagram below recapitulates the hypothesized effects of nearby passes of comet Venus. The seven Venusian markers are shown in dark blue boxes:
Effects of nearby passes of Venus
© sott.net
Effects of nearby passes of Venus

Looking for a Date


Now we are going to look at graphs of earthly records between 12,500 and 4,500 BP and see if there is any date when the seven markers described above spike concomitantly.

Notice that we're not looking at every single pass of Venus yet, because most data don't provide a high enough resolution. Indeed, ice core analysis and the like usually come with a centennial or millennial scale, while Venus, especially during its last passes, must have exhibited an (almost circular) orbital period that is measured in decades.

For reference, according to Velikovsky, the orbital period of cometary Venus was 52 years, the typical period of a solar system comet (Jupiter-family comets) is less than twenty years, and the current orbital period of planetary Venus is only 255 days.

So, we are looking for a span of a few centuries within which the hypothesized passes of Venus might have occurred.

Methane Spike and Temperature Drop

First, we are going to examine two indicators taken together: a methane spike in conjunction with a temperature drop, because methane is a strong greenhouse gas (methane has a global warming potential 28 times that of carbon dioxide), so a methane spike should induce a warming not a cooling. Is there any date between 12,500 and 4,500 BP in which this unlikely conjunction occurred?

The charts below show temperature and methane records over the past 12,000 years. The part on the right with a pink background represents the 4,500 to 12,000 BP time-span.
Temperature and CH4 variation (12ka BP to now)
© Thomson et al., 2006
Temperature and CH4 variation (12ka BP to now)
Over the past 12,000 years, the largest temperature drop recorded in the Kilimandjaro Northern ice field (5 degrees drop, as indicated by the red arrow) and in Israel Soreq Cave (2 degrees drop, as indicated by the yellow arrow) both occurred at the same time: 5,200 years BP (3,200 BC)

At the same date, one of the largest methane spikes over the past 12,000 years was recorded in the GRIP Greenland ice core, as indicated by the pink arrow, with an increase from 600 to 650 ppbv (part per billion per volume). Notice that the methane rise seems to last for a few centuries, which might suggest one lasting event or a series of events shortly interspersed.

Now, Kenya (Kilimandjaro) and Israel (Soreq Cave) are just two locations near the tropics. Was the 5,200 BP temperature drop a local glitch or a global event?

The Greenland ice core (GISP2) also reveals a temperature drop ca. 5,200 BP (see purple arrow in the graph below):
Greenland ice core - temperature over the last 10,000 years
© Alley et al.
Greenland ice core - temperature over the last 10,000 years
Not only does the GISP2 ice core reveal a temperature drop ca. 5,200 BP, but also a sustained and severe decrease in recorded temperatures (see green arrow) over the following centuries (ca. 5,200 - 4,600 BP).

The 5,200 BP marked cooling is confirmed by dendrochronology (study of tree rings) conducted in Ireland:
Tree rings narrowness index (5,500 B.C. - 1,000 AD)
© Baillie et al., 1988
Tree rings narrowness index (5,500 B.C. - 1,000 AD)
In the diagram above the 3,200 BC (5,200 BP) date is highlighted in red. The narrowness index (the narrower the ring, the higher the index) is indicated by the red arrows.

According to dendrochronologist Mike Baillie, the 5,200 BP cooling event was one of the three most severe coolings our planet experienced over the past 7,000 years:
"We ranked a very crude narrowness index, the product rs computed for a 10-yr window. We found that the three highest values in the prehistoric period [were] at 1153 BC, 3199 BC and 4377 BC."

- Mike Baillie, 'Irish tree rings, Santorini and volcanic dust veils', Nature, 1988
Notice also that the cooling recorded ca. 5,200 BP seems to be followed by several centuries of colder-than-usual temperatures, as indicated by the green rectangle showing relatively high narrowness indexes until ca. 4,600 BP (2,600 BC).

The above records coming from Kenya, Israel, Greenland and Ireland suggests that the 5,200 BP event started a lasting cooling episode that affected the whole planet. This period is known as the Piora Oscillation:
The Piora Oscillation was an abrupt cold and wet period in the climate history of the Holocene Epoch; it is generally dated to the period of c. 3200 to 2900 BCE. Some researchers associate the Piora Oscillation with the end of the Atlantic climate regime, and the start of the Sub-Boreal, in the Blytt-Sernander sequence of Holocene climates.
The Piora Oscillation got its name from the Piora valley in Switzerland where the 5,200 BP cooling event was first detected:
The phenomenon is named after the Val Piora or Piora Valley in Switzerland, where it was first detected; some of the most dramatic evidence of the Piora Oscillation comes from the region of the Alps. Glaciers advanced in the Alps, apparently for the first time since the Holocene climatic optimum; the Alpine tree line dropped by 100 meters.
So far we have found one date, 5,200 BP, that shows the unusual conjunction between a methane spike and marked global temperature drops. Let's focus now on the five other Venusian markers and see if they display any spike ca. 5,200 BP.

Deuterium

Deuterium is an isotope of hydrogen - also known as heavy hydrogen. As shown in the picture below, its nucleus constitutes one proton and one neutron, and its symbol is 2H or D:
Deuterium molecule
© Shala Howell
Deuterium molecule
Deuterium is one of the most thoroughly measured chemicals of Venus because deuterium is related to the presence of water which is considered as one of the necessary components for life to develop. So, the study of deuterium on Venus might help answer questions about life on Venus. In any case, deuterium is far more abundant in Venus' atmosphere than on Earth:
"Absorption lines of HDO and H2O have been detected in a 0.23-wave number resolution spectrum of the dark side of Venus in the interval 2.34 to 2.43 micrometers, where the atmosphere is sounded in the altitude range from 32 to 42 kilometers (8 to 3 bars). The resulting value of the deuterium-to-hydrogen ratio (D/H) is 120 ± 40 times the telluric ratio, providing unequivocal confirmation of in situ Pioneer Venus mass spectrometer measurements that were in apparent conflict with an upper limit set from International Ultraviolet Explorer spectra. The 100-fold enrichment of the D/H ratio on Venus compared to Earth is thus a fundamental constraint on models for its atmospheric evolution."

- De Bergh et al., 'Deuterium on Venus: observations from Earth', Science 1991
In her 1997 paper, Donahue found even higher ratios of deuterium to normal hydrogen on Venus compared to Earth: 150 ± 30 or 157 ± 30 or 138 times.

Not only was a high concentration of deuterium found in Venus' high atmosphere, but this deuterium is pushed by solar winds outside the Venusian atmosphere towards Venus' surrounding space and ion tail:
"[...] the motional electric field of the solar wind impressed across the draped magnetic field lines of the ionotail of Venus eventually overtakes the polarization electric field and accelerates the ions up to solar wind speeds as the ionotail merges into the interplanetary medium. Essentially all escape of H* and D* by the electric field process occurs in the light ion bulge, where most of these ions reside."

- Dubinin et al., 2017, The Effect of Solar Wind Variations on the Escape of Oxygen Ions From Mars Through Different Channels: MAVEN Observations
This leakage of deuterium from Venus' high atmosphere to its surrounding space and ion tail make a gas transfer from Venus to Earth more likely if the two bodies are close enough.

In my article titled Did Earth 'Steal' Martian Water, we emphasized that even today, with Venus being a stable planet, it retains a very long ion tail. Venus' tail is 45 million km (29 million miles) long - so long in fact that its ion tail reaches Earth when the Sun, Venus and Earth are aligned.
Venus ion tail

Venus ion tail
It's probable that when Venus was a comet, its ion tail was much larger, hundreds of millions of km long, making the transfer of ions (including deuterium ions) from its tail to Earth possible, even if the two bodies were at a considerable distance from each other.

Now let's look at deuterium records on Earth. Since deuterium concentration fluctuates a lot, we'll focus on the deuterium excess that helps identify spikes more easily:
Deuterium excess over the past 10,000 years
© Masson-Delmotte et al., 2005
Deuterium excess over the past 10,000 years
The above chart shows the deuterium excess found in a Greenland ice core (GRIP). We can see that in 5,200 BP (red vertical line) one of the three largest deuterium spikes of the past 10,000 years occurred, reaching 10.4 excess deuterium, as shown by the blue horizontal line.

Sulfur Dioxide (SO2)

As mentioned above, as far as sulfur dioxide is concerned, Venus' atmosphere contains 186 ppm of SO2 while Earth's atmosphere only contains about 10 ppb - a 20,000-fold difference.

For comparison, the 1883 Krakatoa eruption, one of the largest eruptions in modern history, generated a 40 ppm spike in the GISP2 Greenland ice core.
GISP ice core SO2 concentration over the past 6,000 years

GISP ice core SO2 concentration over the past 6,000 years
In the diagram above, the blue arrow shows a 250 ppm sulfur dioxide spike ca. 5,200 BP (3,200 BC). This is the fifth-strongest sulfur signal recorded over the past 6,000 years.

As we've discussed in previous articles, SO2 spikes are tentatively associated with volcanic eruptions. Interestingly, the 5,200 BP signal is the largest unidentified spike in the last five millennia, as shown by the green arrow in the diagram below:

SO2 concentration in GISP2 ice core (14,000 BC - now)
© Volcano café
GISP ice core SO2 concentration over the past 6,000 years
Carbon Dioxide (CO2)

CO2 is by far the most prevalent gas in Venus' atmosphere (96.5%) while it is only a trace gas in Earth's atmosphere (400 ppm). If there were passes of cometary Venus near Earth ca. 5,200 BP, one could expect a gaseous transfer and a subsequent CO2 spike in Earth records - which is indeed what CO2 concentration measured in the EPICA (Antarctica) ice core suggests:

CO2 concentration in EPICA ice core (11,000 BP - now)

CO2 concentration in EPICA ice core (11,000 BP - now)
Notice that, as with the temperature cooling and the methane spike, the increase in atmospheric CO2 lasted several centuries. As depicted by the red arrow in the diagram above, CO2 concentration rose markedly from ca. 5,200 BP. This rise lasted about six centuries until ca. 4,600 BP, as shown by the green box.

Increased Wetness

Increased wetness is one the effects of cometary events, whether from direct impacts and/or overhead explosions and/or tail crossing. These three features increase atmospheric dust, which in turn acts as a nucleation agent, increasing cloudiness and inducing precipitation. The diagram below illustrates these interactions:

Atmospheric dust increases rainfall
© Seinfeld et al., 2016
Atmospheric dust increases rainfall
The diagram below shows rainfall over the past 10,000 years in the Indus valley. As shown by the red arrow, the 5,200 BP time-mark reveals a sharp increase in rainfall from 450 mm to about 800 mm a year, roughly an 80% increase. In addition this increase in rainfall lasted for several centuries after 5,200 BP, as shown by the green box below

Rainfall over the past 10,000 years
© Lamb et al., 1978
Rainfall over the past 10,000 years
Was the increased wetness ca. 5,200 BP limited to the Indus Valley or was it more like a global event?

Thousands of kilometers away from the Indus valley, increased wetness at this time is confirmed by research conducted around the Dead Sea. In Mount Seldom, 300 feet (100 m) above sea level, lie salt caves. Twigs and leaves from an oak tree (Quercus Calliprinus) were found in one of them, preserved over millennia. How do we explain the oddity of oak fragments in a sterile salt cave 300 feet above sea level?
Now it is geologically certain that it was an ancient pluvial age that created caves in the salt; in fact past climate can be inferred by carefully measuring the width of caves formed by salt dissolution. The cave widths can in turn be compared with correlative glacial advances in northern Europe (bigger caves = more rain = more glaciers) and the cave elevations with ancient sea levels of the Dead Sea itself.

The horizon of wide caves found some 300 feet above the present sea level necessarily indicates an extremely wet period in the early Bronze Age, or about 4200 to 5200 radiocarbon years before present.

Oak twigs, driftwood, and marl found in the caves must have been transported by floodwater from some other part of the Judiah Hills. when the water level was some 300 feet higher than present, implying heavy flooding on the Jordan River and coupled probably with lower evaporation rates due to cooler weather.

- Ignatius Donnelly and the End of the World
The diagram below illustrates the increased wetness in the Dead Sea region experienced ca. 5,200 BP (as shown by the red vertical line). Notice that the wet episode around the Dead Sea lasted several centuries, as indicated by the green box, the end of which occurred between 4,900 and 4,400 BP. Indeed during those 5 centuries the sea level reconstruction is uncertain, as shown by the question marks and the dashed level curve:

Dead Sea level over the past 10,000 years
© Migowski, 2006
Dead Sea level over the past 10,000 years
We find a similar phenomenon on the American continent where the Lago Grande (the main part of Lake Titicaca, along the border of Bolivia and Peru) started to rise ca. 5,200 BP, it lasted for centuries until the lake was about 100 meters (300 feet) higher, which is the same figure we encountered for the Dead Sea rise.

Lago Grande level over the past 13,000 years
© Rove et al., 2004
Lago Grande level over the past 13,000 years
The water rise in Asia (Indus Valley), Middle East (Dead Sea) and Americas (Lake Titicaca) strongly suggests that our planet experienced a marked wetness episode starting ca. 5,200 BP and lasting for several centuries.

Notice however that while numerous areas experienced some increased wettness between 5,200 and 4,600 BP, some other areas experienced an aridification, as was the case for Spain for example:
Palynological data from areas within the thermo- and mesomediterranean areas reported woodland cover reductions after ca. 5200 cal yr BP (Jalut et al., 2000; Carrión et al., 2001, 2004; Carrión, 2002; Pantaléon-Cano et al., 2003; Fletcher et al., 2007) (Fig. 8).

During this period, an increase in fire activity, probably enhanced by arid climate conditions, may have played a crucial role in favoring the spread of sclerophyte and fire-prone communities (Carrión and van Geel, 1999; Carrión et al., 2003; Gil-Romera et al., 2010a), even at high elevations (Carrión et al., 2007; Anderson et al., 2011; Jiménez-Moreno and Anderson, 2012; Jiménez-Moreno et al., 2013).

In addition, marked changes in several lake sequences took place approximately at 5100 cal yr BP. (Carrión et al., 2003; Anderson et al., 2011; García-Alix et al., 2012) . In Villarquemado, deposition in ephemeral lake conditions continued without major changes in the geochemical signature (SUB-2A), except for a significant increase in Mn that might reflect higher occurrence of oxidation processes in a shallow environment.

Other pollen-independent studies reach similar conclusions: at Laguna de Medina, Reed et al. (2001) suggest a clear decrease in lake levels after 5530 cal yr BP, while at Siles phases of dramatic lake dessication around 5200 and 4100 cal yr BP are identified (Carrión, 2002).

- Nick Brooks, Beyond collapse: climate change and causality during the Middle Holocene Climatic Transition, 6400-5000 BP
On the other side of the Mediterranean Sea, in North Africa, a similar aridification took place:
Arid interval 5010-4860 (+/- 150) at Tigalmamine in montane Morocco. Corresponding decline in oaks (Quercus rotundifolia and canariensis) in favor of Gramineae suggests reduced winter precipitation corresponding to cooler sea temperatures in North Atlantic.

- Lamb, H. F. et al, Nature, 373 p 134 (1995).
The above suggests that our planet experienced a dramatic and centuries-long wet period starting ca. 5,200 BP, except South West Europe and North Africa which experienced aridification.

Increased Atmospheric Dust

The hypothesized crossing of cometary Venus' tail, the induced earthquakes and volcanic eruptions, direct impact of cometary fragments and overhead cometary explosions are all potential causes for an increase in atmospheric dust.

Dust analysis conducted in Terra Del Fuego (Argentina) reveals a moderate dust spike ca. 5,200 BP (see purple arrow in the diagram below) This increase in dust concentration lasted a few centuries up until ca. 4,600 BP (see green rectangle).

Note also that 5,200 BP marks the beginning of a period of glacier advance that lasted until ca. 4,600 BP (see blue triangle), confirming the cooling described above.

Dust concentration and size, glacier advance and magnetic susceptibility (8,000 BP - now)
© Vanneste et al., 2016
Dust concentration and size, glacier advance and magnetic susceptibility (8,000 BP - now)
Notice also that median dust grain size increases ca. 5,200 BP, suggesting that the dust source was not winds blowing over an arid region, because this eolian phenomenon tends to carry small dust particles.

Tierra Del Fuego is not the only place that witnessed an increase in atmospheric dust. In Huascaran (Peru), ice cores reveal a similar pattern, with a marked dust spike. A two-fold increase in dust concentration from 15,000 to 30,000 ca. 5,200 BP that lasted until ca. 4,600 BP.

Huascaran dust concentration (10,000 BP - now)
© Thomson et al., 1995
Huascaran dust concentration (10,000 BP - now)
Thousands of kilometers from Peru and Argentina, the African continent experienced dust spikes too. As shown in the diagram below, both the Kilimandjaro ice core and the Gulf of Oman eolian deposition reveal a dust spike starting ca. 5,200 BP (red vertical line) and lasting until ca. 4,600 BP (green box).

Dust concentration in Kilimandjaro and Gulf of Oman
© Thomson et al., 2002 - Cullen et al., 2000
Dust concentration in Kilimandjaro and Gulf of Oman
Notice that in the diagram above, the dust spike in the Gulf of Oman was the second largest over the past 11,000 years.

Similar to the methane, temperature, CO2 and wetness data, dust records reveal a disruption that started ca. 5,200 BP and lasted until about 4,600 BP.

In summary, so far, we have identified seven potential Venusian markers, namely temperature drop, methane, deuterium, sulfur dioxide, carbon dioxide, wetness and atmospheric dust. We have discovered that there's only one time period between 12,600 BP and 4,500 BP that ticks each of those seven markers. This date is 5,200 BP.

Impact On Human Populations

The neolithic age ended around 5,000 BP and was superseded by the Bronze Age. Thus the period we are studying (5,200 - 4,600 BP) corresponds to the late Neolithic and early Bronze Age.

Despite the relative scarcity of archeological data for these remote times, we can see that the Earth changes described above had consequences on the human population. Several cultures and settlements collapsed between 5,200 and 4,600 BP.

In Mesopotamia, the collapse of the Uruk culture after flourishing for 6 centuries has been pinpointed to around 5,200 BP, as Uruk "colonies" in the North were abandoned. Some smaller settlements in southern Mesopotamia were abandoned too. According to Peter Martini and Ward Chesworth, the collapse of the Uruk culture was due to rapid cooling.

Cone mosaics covering a wall in Uruk, Irak
© Benjamin Rabe
Cone mosaics covering a wall in Uruk, Irak
Another example from Mesopotamia is Jemdet Nasr, a settlement mound in Iraq encompassing 5 hectares (14 acres). After two centuries of development, a fast collapse occurred at 4,900 BP. Irrigation cultures continued in the region, but new strong dynasties thrived again in Mesopotamia only after 4,600 BP, after an increase of temperatures and higher precipitation.

In the Nile valley after centuries of an increase in population agglomeration and a parallel increase in social complexity, 5,200 BP marked the collapse of Northern Egypt, which was subjugated by Southern Egypt.

Like in Mesopotamia, the collapse of Northern Egypt is explained by "climatic deterioration":
This occurred against a background of population agglomeration in the Nile Valley at a time of increasing climatic and environmental deterioration and uncertainty, which may have played an important role in driving competition over resources.

Nick Brooks, Beyond collapse: climate change and causality during the Middle Holocene Climatic Transition, 6400-5000 years before present, 2013
According to Vernet et al. (2000), the Sahara region experienced a similar collapse with a sudden and marked reduction in the number of occupation sites north of 23°N over the 5200-5000 BP period. The chart below shows this decrease in human population ca. 5,000 BP (red vertical line) North of 23° latitude (blue columns). The human population decreased by about 50% after more than two millennia of relative stability.

Notice that south of 23° latitude, the population decreased too (purple dashed line) but in a less pronounced way. This depopulation happened after one millenium of sustained demographic growth.

Human occupation of the Sahara
© Vernet et al., 2000
Human occupation of the Sahara
The Knap of Howar on the island of Papa Westray in Orkney, Scotland is a Neolithic settlement which may be the oldest stone building in northern Europe. Radiocarbon dating shows that it was deserted ca. 4,800 BP after 9 centuries of occupation.

The Knap of Howar,  one of the oldest Neolithic complexes Orkney, Scotland
© Message to Eagle
The Knap of Howar, one of the oldest Neolithic complexes Orkney, Scotland
Cucuteni-Trypillia culture is a Eastern European culture that emerged ca. 5,800 BP and flourished for eight centuries. It encompassed hundreds of km2, about 3,000 structures and tens of thousands of inhabitants.

It eventually came to an end around 5,200 BP. For a long time the collapse of the Cucuteni-Trypillia culture was attributed to the Kugan invasion. But nowadays another explanation prevails:
In the 1990s and 2000s, another theory regarding the end of the Cucuteni-Trypillia culture emerged based on climatic change that took place at the end of their culture's existence that is known as the Blytt-Sernander Sub-Boreal phase. Beginning around 3200 BC, the earth's climate became colder and drier than it had ever been since the end of the last Ice age, resulting in the worst drought in the history of Europe since the beginning of agriculture.

- Anthony, David W. (2007). The Horse, the Wheel, and Language
In The Indus Civilization: A Contemporary Perspective, Gregory L. Possehl shows that the end of stage 2 of the Indus civilization occurred ca. 5,200 BP. Eventually, it transitioned to Stage 3 or 'Early Harappan'.

In China, the Yangshao culture existed for two millennia. According to Xiao et al., 2004, around 5,100 BP a cooling episode occurred in the Daihai Lake region (China):

Climate pattern over the Daihai region for the last 10,000 years
© Xiao et al., 2004
Climate pattern over the Daihai region for the last 10,000 years
This cooling episode marked the end of the late Yangshao culture in the Daihai Lake region.
A model of Jiangzhai, a Yangshao village
© Prof. Gary Lee Todd
A model of Jiangzhai, a Yangshao village
Uruk, Jemdet Nars, Northern Egypt, the Northern Sahara, the Knap of Howard, Cucuteni-Trypillia, the Indus civilization and the Yangshao culture all exhibit a similar pattern: after centuries of development, they suddenly collapsed between 5,200 and 4,800 BP.

As shown above most of these collapses are attributed to sudden climate change. However, the collapse of some of these cultures and settlements has been attributed to wars or epidemics.

Climate change, wars and epidemics are not mutually-exclusive causes of collapse. Cometary events can and do cause drastic climate changes as detailed above. But, cometary events can also be the cause of wars (due to the reduced resources) and epidemics (because of cometary-borne pathogens).

Venus: From Comet To Planet

The former cometary nature of Venus has been demonstrated in my article titled 'Did Earth steal Martian Martian Water?' based on geophysical, astronomical and meteorological evidence.

In the same article we've shown that ca. 12,600 BP cometary Venus was already in the solar system and 'pushed' Mars close to Earth. Nowadays Venus is not a comet; it has a stable circular orbit as a planet.

Venus as a planet is attested to as far back as Mesopotamia (ca. 4,500 BP). It means that the transformation of Venus from comet to planet occurred between 12,500 and 4,500 BP. The seven Venusian markers studied above suggest this transformation began ca. 5,200 BP.

This transformation involves an orbital change: a progressive transition from a long duration highly elliptical cometary orbit to a short duration circular planetary orbit. It is the progressive capture of cometary Venus by the Sun that transformed it into a stable planet.

We're looking here for several passes, with shorter and shorter intervals during the 5,200 to 4,600 BP timespan.

Do myths provide any hints about cometary Venus? Its orbital change ? Its number of passes? The effects on Earth of those passes? The time interval between the passes?

Cometary Venus In Myth

The cometary nature of Venus is attested by several myths, among which:
The Aztec Codex Telleriano-Remensis represents Venus as a smoking star in A.D. 1533, linking Venus to imagery of comets {Aveni 1980:27). A Maya text in the Songs of Dzitbalche seems to identify Venus as a smoking star (Edmonson 1982a:183).

- Susan Milbrath, Star Gods of the Maya: Astronomy in Art, Folklore, and Calendars
The Aztec Codex is only one among numerous ancient sources describing Venus as a comet. Most traditions followed the same line of thought:
Each of the goddesses [Inanna, Hathor, Anat, Athena and Kali among others] is explicitly described as a celestial body, identifiable with the planet Venus; and the imagery surrounding each goddess is consistent with that universally associated with comets (e.g., long, disheveled hair; serpentine form; identification with a torch; association with eclipses of the Sun, etc).

- Efemeral Research Foundation, Exploring the Saturn Myth
Not only was Venus described as a comet by numerous ancient mythologies, but it was considered a destructive one, as depicted in the prayer of lamentation to Ishtar:
O Ishtar, queen of all peoples . . .
Thou art the light of heaven and earth. . . .
At the thought of thy name the heaven and the earth quake . . .
And the spirits of the earth falter.
Mankind payeth homage unto thy mighty name,
for thou art great, and thou art exalted.
All mankind, the whole human race,
boweth down before thy power. . . .
How long wilt thou tarry, O lady of heaven and earth . . . ?
How long wilt thou tarry, O lady of all fights and of the battle?
O thou glorious one, that ... art raised on high, that art
firmly established, O valiant Ishtar, great in thy might! Bright torch of heaven and earth, light of
all dwellings, Terrible in the fight, one who cannot be opposed, strong in the
battle! O whirlwind, that roarest against the foe and cuttest off the
mighty! O furious Ishtar, summoner of armies!

- Leonard W. King, Enuma Elish: The Seven Tablets of Creation
Myths depict Venus as a destructive comet, but do they provide any information about the timing of her passes?
[...] the natives of pre-Columbian Mexico expected a new catastrophe at the end of every period of fifty-two years and congregated to await the event. "When the night of this ceremony arrived, all the people were seized with fear and waited in anxiety for what might take place." They were afraid that "it will be the end of the human race and that the darkness of the night may become permanent: the sun may not rise anymore." They watched for the appearance of the planet Venus, and when, on the feared day, no catastrophe occurred, the people of Maya rejoiced.

They brought human sacrifices and offered the hearts of prisoners whose chests they opened with knives of flint. On that night, when the fifty-two-year period ended, a great bonfire announced to the fearful crowds that a new period of grace had been granted and a new Venus cycle started.

The period of fifty-two years, regarded by the ancient Mexicans as the interval between two world catastrophes, was definitely related by them to the planet Venus; and this period of Venus was observed by both the Mayas and the Aztecs.

The old Mexican custom of sacrificing to the Morning Star survived in human sacrifices by the Skidi Pawnee of Nebraska in years when the Morning Star "appeared especially bright, or in years when there was a comet in the sky.

- Velikovsky, Worlds in Collision, pp.155-156
The Mayan and Aztec traditions mention a 52-year Venus cycle; other cultures have similar myths about a cyclically destructive Venus but the duration of the cycle is different. Such is the case in the Etruscan myths:
It can be variation of 52 like in Codex Vaticanus. In the Codex Vaticanus the world ages are reckoned in multiples of fifty-two years with a changing number of years as an addition to these figures. A. Humboldt (Researches, II, 28) contraposed the lengths of the world ages in the Vatican manuscript (No. 3738) and their lengths in the system of the tradition preserved by Ixtlilxochid. According to Censorius it is a 105 year period: Four ages of 105 years are referred to by Censorinus (Liber de die natali) as having taken place, according to the belief of the Etruscans, between world catastrophes presaged by celestial portents.

- Velikovsky, Worlds in Collision, p. 154
And there is a Judaic 50-year Jubilee tradition whose duration is very close to the Mayan/Aztec tradition:
The fiftieth year was a jubilee year [...] The festival of the jubilee, with the return of land to its original owners and the release of slaves, bears the character of an atonement, and its proclamation on the Day of Atonement emphasizes this still further. Was there any special reason why fear returned every fifty years? [...] On the Day of Atonement the Israelites used to send a scapegoat to "Azazel" in the desert.[...] It was also called Azzael, Azza, or Uzza. [...] The Arab name of the planet Venus is al-Uzza.

- Velikovsky, Worlds in Collision, p. 154
So, according to several traditions, Venus was a destructive comet, exhibiting cycles of 52 years (Mayan/Aztec tradition), 50 years (Judaic tradition) or 105 years (Etruscan tradition).

In Mesopotamian mythology, Inanna is Venus, the goddess of war and sex. There is an interesting myth titled "The Descent of Inanna into the Underworld" that goes as follow:
Inanna passes through a total of seven gates, at each one removing a piece of clothing or jewellery she had been wearing at the start of her journey, thus stripping her of her power. When she arrives in front of her sister, she is naked:

"After she had crouched down and had her clothes removed, they were carried away. Then she made her sister Erec-ki-gala rise from her throne, and instead she sat on her throne. The Anna, the seven judges, rendered their decision against her. They looked at her - it was the look of death. They spoke to her - it was the speech of anger. They shouted at her - it was the shout of heavy guilt. The afflicted woman was turned into a corpse. And the corpse was hung on a hook."
To understand the symbolic meaning of this myth, we have to know that in Mesopotamian mythology (and art), the symbolism of nakedness is very specific:
Nakedness, correspondingly, is frequently associated with a state of powerlessness and with captivity and impending execution, not only in Mesopotamian literature but also in art.

- Karen Sonik, Bad King, False King, True King: Apsû and His Heirs
If nakedness equates powerlessness and captivity, could the Inanna myth depict the comet Venus progressively rendered "powerless" and "captured", over 7 passes (the 7 gates of the Underworld), into a circular planetary orbit?

This capture of Venus where she is progressively rendered powerless might be reflected by the removal of one 'item' of hers at each 'gate'. 5 out of the 7 items are jewels. Might this be a symbol of a loss of shiny cometary fragments during each of the seven passes?
At the first gate the great crown is removed from her head, at the second gate the earrings from her ears, at the third gate the necklace from her neck, at the fourth gate the ornaments from her breast, at the fifth gate the girdle from her waist, at the sixth gate the bracelets from her hands and feet, and at the seventh gate the covering cloak of her body.

- Manly P. Hall, Masonic, Hermetic, Quabbalistic & Rosicrucian Symbolical Philosophy
Coincidentally or not, the Aztec symbology represents Quetzacolatl (Venus) as a snake or a dragon (two recurring symbols for cometary bodies).

Often Quetzalcoatl is represented swallowing its own tail like in the picture below. This representation, also known as Ourobouros, symbolizes cycles. Notice that Quetzalcoatl/Ourobouros is usually depicted with seven segments/vertebrae, as indicated by the seven red arrows in the picture below:

Quezatcoatl (Venus) and its seven segments

Quezatcoatl (Venus) and its seven segments
Going back to the Middle East, the Mesopotamians paid very special attention to Innana/Ishtar (Venus). It was one of the most venerated deities in the Sumerian pantheon, the most important and widely venerated deity in the Assyrian pantheon.
Ishtar, "powerful queen [...] is the luminary of heaven and Earth: the greatest Gods have lifted her high, they have made her authority greatest among the gods...they have her heavenly station highest of all whereas at the thought of her name heaven and netherworld quake [...] she alone is "the great one, the exalted one".

- Jean Bottéro, Religion in Ancient Mesopotamia, p 59
According to the same Bottéro, Innana is the divinity to which the most clay tablets are devoted. Inanna appears in more myths than any other Sumerian deity. It was the most observed astronomical body. So, do the numerous Venus observations and the dating of those clay tablets relating to Venus provide any additional clue?

Interestingly, the Innana myth about her descent to the underworld is dated to ca. 2,500 BC (4,500 BP), right after the 5,200 - 4,600 BP destructive episode described above.

Innana on an Akkadian seal. She is equipped with 7 spears, a horned helmet and a 7 segments dress
© Creative Commons
Innana on an Akkadian seal. She is equipped with 7 spears, a horned helmet and a 7 segments dress
Notice that the huge popularity of Innana described above happened quite suddenly. During the Pre-Sargonic era (ca. 4,300 BP) Inanna had virtually no cult despite the fact that Innana was known for nine centuries. Indeed, the earliest mention of Innana dates back to only ca. 5,200 BP:
The earliest references to the name Inanna are on clay tablets from the Eanna district of Uruk; in levels below the remains of major religious buildings dating to the 3rd Dynasty of Ur [ca. 3,200 BC or 5,200 BP]

- Paul Collins, The Sumerian goddess Inanna
In summary, if we are to take the above Sumerian, Judaic, Mayan, Aztec and Etruscan myths as reflections of actual astronomical events involving Venus, we might expect the following:
  • first pass ca. 5,200 BP (first mention of Innana/Venus)
  • 7 passes (the 7 rings of the Underworld)
  • decreasing level of destruction (loss of garments and jewels)
  • 7th and last pass ca. 4,600 BP (first mention of Innana's descent/capture ca. 4,500 BP)
  • time interval between passes is 50 and/or 100 years (Aztec, Mayan and Judaïc traditions)
Do geological, geophysical, meteorological data confirm any of those mythical claims? Thanks to the millennial scale data records studied above, we know that something happened from 5,200 BP to 4,600 BP, but this wide scale doesn't allow a detailed analysis of what happened precisely during those six centuries.

Was it a single event whose effects lasted for several centuries? Was it a series of discrete events? If it's the latter, how many events occurred? At what date? What was the time interval? What was the magnitude of each event?

Zooming in 5,200 - 4,600 BP

It's now time to zoom in and to examine high resolution records. To do so, we have to compile raw data from the ice core (dataset from NOAA or from the NBI).

Here is the bidecadal chart (20-year increment) of the average temperature variations from ca. 5,200 BP to 4,600 BP. This average is based on the temperature reconstructions from five regions: Antarctic, Southern Hemisphere, Tropics, Northern Hemisphere, and Arctic:

The diagram below reveals 7 temperature drops ca. 5240, 5060, 4960, 4860, 4800, 4720, 4660 BP (see dates in red on top of the curve).
ice core temperature reconstruction (5,260 - 4,600 BP)
© Sott.net
ice core temperature reconstruction (5,260 - 4,600 BP)
Notice that overall each pass induces a less severe and less lasting cooling period (shown by the yellow triangles). For example, pass 1 induced a temperature about 15 times more severe and 5 times longer lasting than pass 7. This overall decrease in cooling severity is consistent with progressively less destructive passes of Venus, as suggested by the Inanna myth.

Also note the recurring time intervals between passes (green numbers at the bottom of the chart): 60 years between pass 4 and 5, and between pass 6 and 7, which is quite close to the Maya, Aztec and Judaic tradition fixing respectively the recurrence of Venus passes to 52 and 50 years.

On the same note, the 100-year time gap between pass 2 and 3 and between pass 3 and 4 is very close to the 105 years between Venus returns according to Etruscan mythology.

The chart above suggests that cometary Venus returned every 60 years and every 100 years. So, maybe the two sets of mythologies (Mayan 52- year cycle, and Etruscan 105-year cycle) were both right, only they were referring to different passes of cometary Venus.

Also the interval between each of the seven passes tends to diminish overall from 160 years between the first and the second pass to 60 years between the sixth and the last pass. This overall interval decrease is consistent with a progressive capture of cometary Venus in the Solar system, where its orbit progressively becomes shorter and more circular.

While the time gap between each pass decreases overall, there is however one exception: the time gap between pass 5 and 6 is longer (80 years) than the previous time gap between pass 4 and 5 (60 years).

This non-linear decrease in time intervals between the passes of cometary Venus might be due to the fact that comets, even short period/stable ones, do not return at exact periods because of perturbations caused by astronomical bodies, particularly larger planets.

This variability even applies to the most famous comet of our era: Halley's comet, which has an average period of 77 years, but whose single periods span from 74.33 years to 79 years.
Halley's comet photographed during its last pass in 1986. Its next pass is announced for 2061
© European Southern Observatory
Halley's comet photographed during its last pass in 1986. Its next pass is announced for 2061
Researcher Joachim Seifert came up with a temperature graph similar to the one above, but he added one variable, the Earth Orbital Oscillation (EOO), i.e. the temperature changes induced by the variation in Earth's orbit.

Because of the limited temperature variations induced by this EOO variable, it is neglectable when dealing with major events on a millennial scale, but it is relevant when dealing with high resolution temperature reconstructions:
The upper and the lower Earth orbital oscillation line, within which the Earth climate varies, if not impacted by large cosmic bolides. As we demonstrate, the Holocene temperature evolution does not remain confined within these upper and lower horizontal lines, because strong cosmic impacts always and necessarily produce a strong temperature down-spin spike, followed by a strong upward temperature rebound spike, regressing thereafter. This is the so-called Z-shaped temperature pattern of each cosmic impact on Earth.

- Joachim Seifert, Climate Pattern Recognition In The Mid-To-Late Holocene
Here is Joachim Seifert's temperature graph:
EOO temperature reconstruction (3,400 - 1,600 BC)
© Seifert et al., 2016
EOO temperature reconstruction (3,400 - 1,600 BC)
In the graph above, the time period we're studying (ca. 5,200 - 4,600 BP) is in pink. The green dotted line is the theoretical Earth temperature if the only driver was the Earth Orbit Oscillation (hence the sinusoidal shape). But we can see that the recorded temperature curve (solid black curve) departs from the theorical EOO curve in several places.

Seifert lists 4 catastrophic events that caused some of those departures.

- First pass ca. 5,210 BP (3,210 BC): hypothesized to be related to the Andaman Gulf impact, shown by a red arrow in the graph above:
The BC 3200 event is recognized in lake filling data, both at Lake Accesa and Lake Constance, as described before. The BC 3200 [...] The BC 3200 cosmic impact produced a Z‑shaped temperature pattern, which lasts until 2900 BC. This cosmic impact is responsible for the delayed temperature peak at 3000 BC, displacing the regular peak at 3081 BC by 80 years.

Looking for prospective impact candidates of this time, we found a cosmic meteor impact, striking the Andaman Sea. At Cape Pakarang (west coast of Thailand), a mega-‑tsunami struck (Neubauer, 2011) at 3200 BC, as an outstanding megatsunami event. Regular seaquake tsunamis are not forceful enough to destroy reefs and to move enormous cut-­‐‑off reef-­‐‑boulders far inland.

- J. Seifert, F. Lemke: Climate Pattern Recognition in the Mid-­Holocene (4800 BC to 2800 BC)
Notice also that one the greatest volcanic eruptions of the past 10,000 years also happened ca. 5,200 BP (3250+/- 200 B.C). It produced 175 ppm of sulfuric acid fallout and is attributed to the Akutan volcano in Alaska, USA.

- Second pass ca. 4,807 BP (2,807 BC)
: the Burckle impact, shown by a dark green arrow in the graph above:
[...] the Burckle impact (Gusiakov, 2010; AbboM, 2006). The date 2807 BC is given in Chinese celestial observation records. This impact was enormous in size and effect, the impact crater is 20 km in diameter. This impact sent global temperatures instantly deep down, the enormous fall-out of atmospheric moisture produced widespread global inundations.

- J. Seifert, F. Lemke: Climate Pattern Recognition in the Mid-­Holocene (4800 BC to 2800 BC)
4,807 BP is also the suggested date for an asteroid or comet impact occurring between Africa and Antarctica, around the time of a solar eclipse on May 10, based on an analysis of flood stories - possibly causing the Burckle crater and Fenambosy Chevron.

- Third pass ca. 4,700 BP (2,700 BC): The Campo de Cielo impact shown by a red arrow in the graph above:
Campo de Cielo impact at 2700 BC. The literature (Barrientos, 2014) actually sets a time frame of 2840-2146 BC, but the only impact date remaining is at 2700 BC. This impact is small to medium, delaying the temperature recovery after the Burckle event by one century.

- J. Seifert, F. Lemke: Climate Pattern Recognition in the Mid-­Holocene (4800 BC to 2800 BC)
- Fourth pass ca. 5,080 BP (3,080 BC): Seifert identified a fourth departure from the EOO curve that he attributes this time to a potential mega-eruption (see turquoise trough in the diagram above).

Interestingly, the 5,080 BP event coincides with the largest suspected volcanic eruption over the past 9,000 years, with 255 kg/km2 of acid fallout (sulfuric acid - H2SO4), recorded in Greenland. Notice that this alleged mega-eruption has not been attributed to any known volcano.

Major eruptions over the past 9,500 years
© Hammer et al., 1980
Major eruptions over the past 9,500 years
For comparison, the eruption of Krakatoa in 1883 'only' generated 21 kg/km2 of acid fallout in Greenland. That's 12 times less than the 5,080 BP event.

In addition to the suspected mega-eruptions, a cosmic impact was documented about this time, 3050 BC (5000 cal BP): The Morasko Crater Field in Poland (Wojciech, 2012). This impact field contains 8 smaller craters; peat sequences with meteor metal spherules were dated.

On top of the 4 departures from the EOO curve spotted by Seifert, there are 3 additional discontinuities, occurring towards the end of the 5,200 - 4,600 BP period. Their dating corresponds to the three last and lighter passes of Venus:

- Fifth pass ca. 4,960 BP, as indicated by the dark blue arrow in the EOO diagram,

- Sixth pass ca. 4,870 BP, as indicated by the light green arrow in the EOO diagram,

- Seventh pass ca. 4,650 BP, as indicated by the turquoise arrow in the EOO diagram.

The Seifert EOO diagram is based on Greenland ice core (GISP2), while our duodecenal diagram is based on the average temperature recontruction from 5 regions: Antarctic, Southern Hemisphere, Tropics, Northern Hemisphere, and Arctic. Despite using different sources, both diagrams provide a strikingly similar image: 7 temperature drops with virtually the same timing.

GISP2 VS. region average temperature reconstruction
© Sott.net
GISP2 VS. region average temperature reconstruction
As shown in the table above, for the 7 events described previously, the dating difference between the GISP2 temperatures and the regional average reconstruction is only 13.8 years. It is not a bad match at all for events that happened about 5,000 years ago, knowing that the error margin for ice core dating is typically 2%, i.e. about 100 years for events that occurred 5,000 years ago.

Conclusion

Most literature dealing with cometary events posits regular cycles or a one-time event. While it is often true, it's not the whole picture. The seven passes of Venus described above were neither a one-time event nor part of a constant cycle.

Cometary events can be ongoing or a thing of past. Likewise they can be periodic, pseudo-periodic or a one-shot event.

For example, we know of ongoing periodic cometary cycles like the 27.9 million year cycle followed by Nemesis and its accompanying cometary swarm (see chapter 13 to 19 of Earth Changes and The Human-Cosmic Connection) or the ongoing 3,600 year cometary cycle described in my article 'Volcanoes, Earthquakes And The 3,600 Year Comet Cycle'.

There are also ongoing pseudo-periodic cycles like Comet Halley, whose average period is 77 years, but whose single periods span from 74.33 years to 79 years.

There are one-shot events like the 12,900 BP cometary event described in my article 'Of Flash Frozen Mammoths and Cosmic Catastrophes'.

And finally there are past pseudo-periodic comets like cometary Venus from 5,200 BP to 4,600 BP with decreasing orbital period: from 160 years for pass 1 to 60 years for pass 7.

In my previous 3 articles, I dealt mostly with cometary events:

Of Flash-Frozen Mammoths: Cometary event that triggered the Younger Dryas

Did Earth 'Steal Martian Water? Cometary Venus pushed Mars close to Earth

Volcanoes, Earthquakes And The 3,600 Year Comet Cycle

All of these refer to ancient history. Cometary events seems so remote when observed from a human timescale. However, in 2013 the Chelyabinsk overhead explosion released 30 times more energy than the Hiroshima bomb and damaged more than 7,000 buildings.

More recently, the meteor impact in Akure, Nigeria that created an 8-meter-deep, 21-meter-wide impact crater and destroyed 70 buildings reminds us that cometary events are not just an abstract concept that belongs exclusively to the distant past.

The crater left by a meteor impact in Akure, Nigeria
© PMNews Nigeria
The crater left by a meteor impact in Akure, Nigeria
Despite their apparent remoteness, cometary events are very real and might actually be one of the main punctuators of life and death on Earth. Most mass extinctions were triggered by cometary events and, interestingly, they were followed by the appearance of more complex forms of life.

We can witness this phenomenon, for example, at the Eoceone-Oligocene (E-O) boundary where numerous Eocene species went extinct and were "replaced" by the more complex Oligocene fauna:
Even more open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleocene epoch 30 million years earlier. Marine faunas became fairly modern, as did terrestrial vertebrate fauna on the northern continents. This was probably more as a result of older forms dying out than as a result of more modern forms evolving.
Source
There is a similar pattern at the Cretaceous-Paleogene (K-Pt) boundary (attributed to the Chicxulub impact) where numerous Cretaceous species went extinct and were 'replaced' by the more complex Paleogene fauna:
The Paleogene is most notable for being the time during which mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous-Paleogene extinction event that ended the preceding Cretaceous Period.
Source
If major cometary impacts trigger jumps in the complexity of life on our planet, the question is: how? One possible mechanism is via cometary-borne viruses. The presence of organic material in comets is now hypothesized by mainstream science. And we know that viruses can transfer DNA to their hosts.

Cyanobacterial filaments in the Murchison CM2 meteorite
© NASA/MSFC
Cyanobacterial filaments in the Murchison CM2 meteorite
So, are major cometary events the window of opportunity that 'intelligent design' uses to remove obsolete life forms (mass extinction) and to introduce more elaborate life-forms (life explosion) via the new DNA codes carried by the accompanying viruses?

That will be the topic of a future article.