TECTONICS BLOG Rev. 2021-06-24
Gregory Charles Herman, PhD   Flemington, New Jersey, USA

One bad period on Earth about 800,000 B.P.

On the day following my 65th birthday I started focusing on the large-impact scenario of Australia using Google Earth.  Much to my surprise, lying right beside the confirmed Acraman impact in south-central Australia is what I suspect to be an enormous asteroid-impact strewn field event of probable Mid-Pleistocene age that covers the eastern third of the continent. This event likely ties together 1) the Australasian Tektite field, 2) long lasting, global-climate change at that time, 3) our last geomagnetic reversal, and perhaps even, 4) the demise of Peking Man (fig. 1). All of these events date to within about 12,000 years of 790,000 B.P. (before the present) considering time-measurement errors!  What a tumultuous time that must have been for Earth's creatures, especially those living in the eastern hemisphere.

Figure 1. A summary of climate indicators for the past 3 million years and references to associated phenomenon.

Climate cycles

At this stage of the investigation, three primary, suspected craters are mapped as part an enormous impact strewn field covering the eastern third of Australia, with the largest and leading crater buried beneath the Bass Strait north of Tasmania (fig. 2). This is apparently the first in string of craters spread over an enormous impact strewn field estimated to be 800,000 years old, the age of the associated tektites (figs. 3-5).  Global gravity and magnetic potential-field anomalies show that the event happened along a ~355o heading and appears to be of low- to moderate incidence (estimated to be less than 45o) based on it's elongate, tapered geometric nature. I am unsure whether this represents a fragmented strike from impacting at a low-angle of incidence, a dissociated parent body ricocheting across the landscape, or a set of bolides coming in to bear on Earth like a string of pearls, but this event was BIG. Many Earth-systems were disrupted in it's wake. Estimates of the bolide size stem from the volume of tektites in the Australian tektite field that cite a 20-km object, or one roughly the same as that which excavated the Gulf of Mexico at the Mesozoic-Cenozoic time boundary (Chicxulub ~ 66 Ma).

Figure 2. The Suspected Eastern Australian Impact Strewn Field

Eastern Australian strewn field Eastern Australian strewn field Eastern Australian strewn field

Figure 3 details the locations of three of the bigger, suspected craters, although there seem to be many more.  These three are aligned along the ~355o heading and most likely stem from a low incidence angle with secondary splatter and fragments peppering the countryside. It appears that different regions in the surrounding Australasian tektite field show morphological and chemical dissimilarity owing to where they're located, but this aspect requires much more study.

Figures 4 and 5 show how this relates to the the enigmatic Australasian tektite field (figs. 3 and 4). It all seems to correlate very nicely, but awaits field confirmation. Any help with that would be appreciated.

Figure 3. The largest, suspected crater locations.  

Eastern Australia strewn field Crater No. 2 No. 3 

The distribution of the Australasian tektite field appears to reflect the counterclockwise rotation of Earth, with airborne ejecta falling over an area reflective of such dynamics. This aspect will also require more robust modeling reflecting atmospheric transport. The large quantity and size of the glass shards that rained down on man during this event is astounding as characterized in figures 4 and 5 that include a spatial comparison of the Australasian tektite field and the suspected, East Australian strewn field (EASF).

Figure 4. Spatial comparison of the Australasian tektites and the East Australian strewn field

Eastern Australian strewn field and the Australasian tektite field

Figure 5 is a photograph posted on line in Wikipedia commons that was taken by James St. John, a geology professor at Ohio State University, Newark Campus. When asked through correspondence, he told me that the photograph was taken at the Cincinnati rock and mineral show. This photo includes samples of the material collected form the tektite field that exemplifies the glass bombs and particles that rained down on Earth's surface at that time.

Figure 5. A photograph showing mid-Pleistocene objects from southeast Asia.

Wikipedia picture
Photo by James St. John, Ohio State University, Newark, Ohio; Cincinnati rock and mineral show

Earth's climate underwent a major shift about 800,000 years ago when its long-term oscillatory cycles of hot versus cold extremes transitioned from 41,000 year cycles before to 100,000-year-ones afterwards. One can debate when this transition took place from the various temporal metrics (fig. 1), but 800,000 B.P. appears to be as robust candidate for a defining line as those near to it. When considering the accurately dated 800,000 year-age for the tektites, it is likely that these events are related. Even more so because of the small lapse of geological time between 800,000 B.P. and the last geomagnetic reversal, about 12,000 later. 

A pertinent question thus arises: is 12,000 years he time needed for Earth to adjust to such an energy flux? That is, 12,000 years of ensuing lithospheric flexure and changed mantle dynamics needed to reconfigure Earth's magnetic armature? And what about the climate-frequency change? Does that result from a sudden perturbance to a pre-existing axial wobble? Epeirogenic uplifts seem to correspond spatially with the 2900-km radius rings circumferentially drawn around this strewn field (fig. 2). Tasmania was glaciated for the first time in the mid-Pleistocene, when the entire Australasian region was uplifted. Again, what a tumultuous period that must have been. More work is also needed in bringing together data that will perhaps disclose the demise of Peking Man. At this point, I am still startled by the temporal coincidence between the four enigmatic circumstances noted above in figure 1 and the apparent, common link to the EASF. Impact tectonics is a plausible mechanism to account for that synchronicity.  But alas, this may just be another of my 'far-field' ventures of highly speculative nature that still needs ground truthing. That's one problem with virtual intelligence; it leaves a lot to be desired. Stay tuned.