What are the chances of finding a sample of earth atmosphere that was sealed in a very high-purity glass capsule with centimeter thick walls 780,000 years ago? A pristine sample before mankind had done anything to modify the air—no industrial revolution, no nukes, and no fluorocarbons. Homo erectus was still struggling to tame a campfire.
We do have such samples, preserved in a significant number of tektites. Not just tiny samples either, but big bubbles in some cases making up 40% or more of the tektite’s volume. In the image above, I have included two broken specimens to illustrate typical “capsule” wall thickness. The big Lei gong mo on the right weighs 328.9 gms, but given its volume, it should weigh 471.5 grams. It contains a bubble amounting to 30.2% of its volume. The example at center bottom was a new find from Tucson this year, a 54.9 gm spheroid that is 35% void space. And at lower left is our all time biggest bubble (relative to the size of the tektite): 54.7 grams, a whopping 43.7% bubble. With a density of 1.357 gm/cc, this one will almost (but not quite) float in saltwater!
These bubbles and their contents have received some academic attention in the past. We know something of their internal pressures and gaseous make-up, but much of the work is severely dated and incomplete in view of what could be done with current technology. It has long been known that the internal pressures correspond to conditions at an altitude some 40 to 50 km above earth’s surface. In the older literature it is often postulated that this suggests the altitude at which the bubbles closed, but there is the issue of extremely hot gases being involved with subsequent pressure changes related to cooling and condensation. Further, there is some concern that these very low pressures may be partly the result of water vapor reacting with the bubble walls to form hydration rinds. On the other hand, there is evidence that modern neon and helium have been able to diffuse through the glass into the bubbles.
But in any event, these hollow tektites probably offer the best samples of 780,000 year old atmosphere we are ever likely to obtain. They offer an unsurpassed opportunity for comparative atmospheric studies, which to the best of my knowledge have not been undertaken. As atmospheric research becomes more and more sophisticated and questions about ozone destruction, greenhouse gases, airborne pollutants, nuclear testing residues and similar matters rise in importance, how helpful might it be to have such a pre-human-impact baseline sample?
If forced to answer “what is the most important thing that tektites have to offer to science? (—that we know about right now—-), I would have to point at these unthinkably ancient atmospheric samples hermetically sealed in high-quality glass!