Seventh attempt to write this piece? Why?
The late Darryl Futrell, one of the greatest tektite aficionados of all time, was well-known for his belief that Muong Nong-type layered tektites held the keys to the kingdom of tektite mysteries, In his failing years, he sold off his world-class tektite collection in successive waves to help cover his medical bills. In the end, he became fully blind. But still, he retained crates and boxes and drawers and bins of tektites of all sorts including some of his favorite pieces. It was my privilege to catalog, appraise, and eventually broker (to a new museum), the collection he held back until the end. I never met him, but I feel I know him very well. We could’ve been dear friends. We would’ve had great fun discussing this fabulous Muong Nong!
I asked for, and kept, only one stone from the many thousands in his final collection. A 458.3 gram palm-sized layered tektite with deep bread crust-shrinkage cracks—a sharp crocodile-skin texture—, the most unique that I saw in his many hundreds of pounds of Muong Nong “keepers”, (and you must remember, he was perhaps the greatest lover of Muong Nongs ever). See figure 1. Layered tektites are well-known for their blocky fragmental character. It is rare to see remnants of primary external morphological character of any sort, but this one has skin!. I always considered this a superb and interesting specimen, but it was only now, as I began to write this article, that I began to grasp the story it has to tell. Futrell was quite right in his belief that Muong Nongs offer important insights.
There is not space in this forum to write the book that is now needed. Why is this my Seventh Sojourn—my seventh attempt to get this story on paper? Every time I consider this rock, more ends connect and I find it impossible to write of any detail without expanding into some whole new quantum universe of thought. Every draft spirals out of control. Even now, I need to apologize both to my readers and my references. Of necessity, I have had to forego formal source citations and a great deal of supportive detail. Initially, the story and the images expanded to include clues from all of the Muong Nongs in our collection. Truly, a book should be written. But this story started with a single special rock, and in the end, I have returned to that centerpiece to find my muse.
As my fingertips explore this piece, I feel I am wearing the spirit gloves of Futrell. I am certain that this very stone, was explored by his fingertips. I imagine his presence as I study this specimen. On that stone our fingers touched across time and the torch passed.
It falls to me to relate the story of this stone. The discussion that follows draws freely from a great deal of published research and also took inspiration from many years of geological fieldwork in the extensive welded ashflows of the great “ignimbrite flare-up” of the American Great Basin country. I find in the latter unambiguous parallels and insight.
With that, the story opens. Some 780,000 years ago there was a cosmic event quite unlike anything mankind has experienced (unless we include Homo erectus, who was on hand for this catastrophe). There was a shower of bolides, probably cometary fragments, that streamed into the earth (or, more properly, into earth’s atmosphere). Over the course of a few hours, a train of gravitationally-fragmented cometoids, something like 20 or 30 pieces ( and maybe as many as a hundred), was intersected by earth. This shotgun blast of structurally weak bolides triggered a series of great aerial bursts. There were few if any cratering events, as very little material had sufficient cohesion to penetrate earth’s atmosphere to reach the ground. But there was unthinkable energy to dissipate, which in this case would take the form of searing white-hot fireballs mushrooming into deep sky from explosions that make our 100 kilotonne bunker-buster bombs look like baby’s toys. Magma-hot glassy ash settled in gusting layers at quieter spots in the deep turbulence.
As the dune of frothing particulates vacuumed from the face of the earth by the first aerial burst gradually deflated into bubbly glass, shrinking and cracking like bread crust, a basal vitrophyre formed, precisely analogous to features commonly seen at the base of volcanic welded ashflow tuffs. Together, the surficial bread crust layer, a variably welded vesicular interior zone, and the basal vitrophyre compose a cooling unit, in the case of the Futrell 458.3 gram Hainan Muong Nong, about 2 inches in thickness (see figure 4).
The presence of a distinctive basal vitrophyre is highly significant, as it implies an adequate residual heat budget within the ash layer itself to achieve dense welding and out gassing. This was not a surface deposit fused from the top down by a blistering overhead explosion although that may have played a role in the fining of the surface layer and the slumping folds often seen in Muong Nongs. The basal vitrophyre indicates a location that received direct and local fallout from an aerial burst. The ash consisted of fragmented magma that welded and deflated into semi-liquid behavior by merit of internal residual heat when it came to rest. The layering represents sedimentary accumulation, not viscous flow-banding, although in cases of advanced welding, the sedimentary layers were exploited by flowage. Muong Nongs formed in the immediate vicinity of the responsible heating event, probably directly below the aerial burst.
Herein are the seeds of a most important insight. The known distribution of Muong Nong layered tektites within the Australasian field has a heartland about 1100 km X 800 km, covering parts of Vietnam, Laos Thailand, and Cambodia. Although oceans confuse the view, there appear to be isolated populations in the Philippines and on Hainan Island, China (the source of the Futrell specimen here described). While there are several examples of tightly clustered finding localities in areas some 30-40 km in diameter, a great many of the reported sites are separated from their nearest neighbors by 50 to 100 kms or further. I believe that each of these localities corresponds to the location of one or more distinct aerial bursts.
It should also be pointed out that these rocks were not ejected into their present locations by a single deep cratering event. (It is not strange that we have been unable to identify a source crater for the 780,000 year Australasian tektite event. There isn’t one). The key inference is offered by the isotope 10Be. Tektites are relatively enriched in the beryllium-10 isotope, which is formed by cosmic ray bombardment and on earth is largely limited to the upper meter of soil where it collects as it washes out of the atmosphere. It decays radioactively such that it is undetectable after about 10 million years on earth. A crater blasted into bedrock over 10 million years old would produce ejecta devoid of any measurable 10Be.
The 10Be-rich raw material for tektites (of all types) is found in and restricted to surface soils! Not exclusively soils, but soils in large enough proportion to donate measurable 10Be to the impactites formed. The chemistry does indicate compositional variations consistent with mixing of two materials, presumable surficial soils and shallow underlying bedrock. The presence of coesite, a high-pressure polymorph of quartz, in a minor percentage of tektites does indicate some contributions from cratering, but it is most consistent with the chemical data to picture a massive aerial burst that vacuumed loessitic soils and limited underlying bedrock into a billowing fireball mushroom cloud. Chemistry also indicates systematic geographic zonation in Muong Nongs, more like compositions related to regional patterns of soil types, not some singular source.
But we are getting ahead of the story in Futrell’s rock. Fused onto the bread-crusted surface of the specimen is a little knob of dense, low-vesicularity resinous-lustered glass with upward closing shrinkage cracks. It may be a small bit, but it is huge in significance. It is a fragment of the basal vitrophyre of a second cooling unit! After the first layer formed, there was sufficient time for welding, out gassing, and shrinkage to form the alligator-skin crust seen in figure 1. Then another layer arrived! The stone itself presents direct and unequivocal evidence of two aerial bursts. This is consistent with the immense geographic distribution of Muong Nongs which requires not one, but a constellation of impactors. As I scan the map, I see on the order of 30 localities which I believe to represent discrete events, not counting impacts in the Philippines or in the oceans! The Futrell stone indicates two aerial burst fireball events affecting the same target area on Hainan Island, probably at least tens of minutes if not hours apart, presumably the product of neighboring cometary fragments following one after the other on the same trajectory. Given that such multiple impacts are to be expected if the individual bolides resulted from the disruption of a single cometary body, as well as the large areas of open ocean in the target region, it is not a stretch to expand my 30 localities into upwards of a hundred aerial burst events.
So the vision of a very large Tunguska-like aerial burst morphs into visions of Comet Shoemaker-Levy 9 versus Jupiter. It is easy, given our earth-centered frame of reference to imagine that those flashes we saw when the comet fragments streamed into Jupiter were monstrous impact explosions, (which they were, but not impacts on a terrestrial surface). Jupiter is gaseous. Everything that happened there was in the “sky”. Those flashes were aerial bursts that were significant events at the scale of planet Jupiter!
If earth encountered even a tiny version of Shoemaker-Levy 9 in the deep past, how would we know? What would we seek as evidence in the geological record?
There is strong agreement that a great many cometary bodies are structurally weak and can be tugged into pieces by gravitational forces even in deep space. Shoemaker-Levy 9 was torn asunder into a trail of fragments by the acceleration of Jupiter’s gravity. If we are seeking evidence of cometary (or subcometary) aerial burst events, Muong Nongs take center stage. Darryl would be thrilled.
Whatever hit our planet 780,000 years ago wasn’t a planet killer (I am betting a Shoemaker-Levy 9 would’ve taken us out without much drama.) I envision a full spectrum of sizes of cometary bodies (or their fragments) with varying densities traveling their foreordained paths through the deeps. We were lucky to get one that sprinkled debris over a third of the earth without any known lasting damage.
Here is the vision elaborated from the Futrell stone:
There came a rushing light so bright that closed eyelids gave no relief! It was silent as it grew in burning intensity, for it far outran the sound of its coming. It sprayed into arcing strands, subdividing like a long trailing firework. Then the first pieces encountered the denser atmosphere and there was near-instant conversion of cosmic speed into an intense flash of heat and light and shock. A blinding fireball of indescribable strength billowed into the heavens vacuuming the face of the underlying earth with mighty winds, spinning like clustered tornadoes. All the loose soil and a fair depth into the underlying bedrock was sucked directly into the heart of the inferno, where the beast was drawing its deepest breaths.
Expanding volatiles fragmented the resulting fully molten glass particles which swirled entrained in the blistering turbulence until sprinkled to earth at some calmer harbor in the storm. There, the fragments resumed their liquid state and fused together into a foaming froth and, ultimately in advanced cases, into dense glass, revealing its layered history only along chilled edges. A centimeter in, a polished sawcut etched with HF reveals little or nothing of the layering in the most densely welded Muong Nongs.
The train of cometoid fragments streamed earthwards, each terminating with the billowing fireball of an aerial burst, something like a swarm of near-simultaneous Tunguskas and larger, spread in a shotgun pattern over a region a couple thousand kilometers across.
I am still unsure where the splashform tektites enter the story. That is for another time, but the Muongs Nongs tell a story like that of Shoemaker-Levy 9. The target area was in eastern Thailand and southern Laos, but there were aerial bursts as far as Hainan to the northeast and the Philippines to the southeast. It is time to quit talking about the missing crater. There isn’t one. There are probably some little ones, but whenever investigated, researchers conclude early on (and correctly) that suspect crater x was not of sufficient size to account for the calculated volume of tektites spread from southern China to Antarctica. “This cannot be the source.” Indeed, one crater cannot be the source.
The vision, through eyeglasses of 10Be, shows a radiating and branching sunburst of great fingers of plasma buzzing across the face of the earth below the aerial burst, ripping up contrails of soil and shallow bedrock, feeding it to the great mushroom in the sky.
I think that the sub-cometary fragment constellation approached from the northwest and the majority of the aerial bursts centered on the border region of eastern Thailand and southern Laos (where the village of Muong Nong is memorialized in the name of the layered tektites found there). Outlier bolides apparently impacted Hainan Island, the Philippines—and maybe even coeval Belize?
For those who may wish to pursue the subject further, I recommend two references in particular:
Wasson, J.T., 2003, Large aerial bursts: An important class of terrestrial accretionary events, Astrobiology, v.3 No.1, pp. 163-179
Schnetzler, C.C., 1992, Mechanism of Muong-Nong-type tektite formation and speculation on the source of Australasian tektites, Meteoritics 27, pp. 154-165