Close to 66 million years ago, an asteroid struck the Earth close to the Northern end of the Yucatan peninsula, leaving a crater close to 125 miles across. As of February 24 of this year, scientists working at the University of Texas, Austin have been able to conclusively link the impact site just off the coast near Chicxulub, Mexico To the extinction level event that eliminated %75 of life on the planet near the end of the Cretaceous period. The UT researchers were able to place the dust settling of the impact to within 2 decades, and speculated that the global winter could have been as short as that - but due to separate research on the eruption of Mount Pinatubo in the Philippines in 1991, we now know that even the low-density ash from a major volcanic eruption will have mostly settled within a matter of weeks, even days - not years. So, if it was not a dust-cloud induced winter that was responsible for the loss of most of the world's megafauna and megaflora, what was the culprit?
A more recent extinction level event might lend some clues: Within 30 million years, large animals were once more beginning to appear on Earth, this time from the family Mammalia. Wooly mammoths, giant sloths, rhinoceroses, and giant deer flourished up until just a few thousand years ago, when it is suspected that another impact event occurred, from a comet this time, not an asteroid, and with multiple impact sites. At this moment, the data is still being collected, and debates are still being held regarding the theory - if research comes along at the same pace as the findings for the K-P boundary Extinction event, the science won't be 'settled' for another forty years - but if true, then this event that occurred nearly 13,000 years ago would have made such changes in the climate as to make it impossible for many of the large land mammals to continue living. Aside from size, the difference between dinosaurs, wooly mammoths and human beings is this: Those creatures that went extinct when their environments changed were not able to adapt to the changes, humans were.
The Younger Dryas period was a global cooling event that commenced nearly 13,000 years ago when (it is suspected) that meltwater lakes on the receding glaciers burst, sending vast amounts of water into the world's oceans, halting the circulation of warm currents from the tropics to the polar regions. Any human living at the time would have been witness to sudden rises of water levels, especially in coastal areas and low lying inland waterways. Survivors would have told tales of great floods and unusual torrential rains that lasted for extended periods. If the bursting of those lakes had been precipitated by the suspected cometary impact, those tales would recount another interesting occurrence: Large animals of all sorts would begin to disappear, and lifespans would become shorter.
The vast amounts of food required to feed the dinosaurs of the old Cretaceous period has been explained away by suggesting that there must have been up to four times today's amount of CO2 in the atmosphere - a concentration of 1600 parts per million (%.16) would provide for an abundance of plant life - but Then there is also the problem of the sheer size of those creatures, as well - surely a large amount of oxygen would be required to keep such massive beasts going, but their lung capacities were not disproportionate from animals of today. There is only one hypothesis that satisfies the requirement for large amounts of carbon and large amounts of oxygen: Atmospheric density was higher on planet earth during the time that these creatures lived. Multiple impact events over time have stripped away large amounts of earth's atmosphere, shortening life spans, and preventing animals from reaching large sizes.
One of the adaptive strategies that our ancient ancestors employed was to use caves for shelter when climate conditions changed dramatically: and caves make excellent sense: the average temperature between 20 and 30 feet below ground stays within the range of 50 - 60 degrees F year round. Caves don't require much fuel to keep warm, and when your civilization's ability to make electricity is lost suddenly, they don't need air conditioning to stay cool. The downside to living in caves is that the size and location are mostly up to nature. Not having a convenient cave nearby was no deterrent to many ancient peoples; they simply built their own 'artificial caves' such as the cliffside pueblos of Mesa Verde that housed up to 1,500 people, or the vast complex of Derinkuyu in the Anatolia region of Turkey whose population numbered in the tens of thousands.
In the current era, artificial caves are made of wood and brick, or sometimes out of glass and steel. In order to compensate for their inherent lack of temperature control, they are heated by burning fossil fuels or sometimes wood, and cooled by way of machines that run on electrical power. As anyone who has ever experienced a prolonged power outage during a winter ice storm can attest, these are some very serious and potentially life threatening design flaws. These homes are completely dependent on a functioning supply chain in order to remain habitable, and as such are not permaculture habitats. Perhaps there is a way to get the advantages of an actual cave in an 'artificial cave' ..
"In a hole in the ground, there lived a hobbit" Author JRR Tolkien Published the famous book in 1937, and at that time, the concept of living in a hole in the ground seemed quaint, perhaps even a bit charming .. but practical? Although people have been using some form of geo sheltering or another for as long as there have been people, the concept did not begin to make a re-appearance in the modern era until the 1970s, when building 'earth ships' out of rammed earth and old tires or 'cob' houses began to become more common. To this day, houses of this type are still associated with counter-culture, and that association might be one of the reasons that they never have taken a more prominent place in modern architecture - difficulties in meeting universal building codes and perceptions that these kinds of structures are unsafe are also contributing factors.
Although the picture above is from the movie set of "The Hobbit" in New Zealand, and is only a façade, real versions of 'hobbit holes' DO exist, and their construction is not significantly difficult, being essentially a concrete dome structure that has been buried, or at least partially buried. Burying concrete tends to preserve the material - I have excavated old sites where the concrete slab had been exposed to weather in places, and remained buried in others, and found that despite many years, the buried parts still looked like fresh concrete, even though the exposed parts had begun to crack and deteriorate. Modern construction techniques greatly improve the aesthetics and durability of geo sheltered homes - there are even companies such as green magic https://greenmagichomes.com/ (unaffiliated) that build and sell modular shells made of polymer that can be assembled on-site, and custom finished in whatever way their clients desire. For the person who wants a custom build, but would rather let the professionals handle all aspects of construction there are companies like Terra Dome https://www.terra-dome.com/?gclid=Cj0KCQiAhP2BBhDdARIsAJEzXlGZpBx5kiojnjLuKuZYrpW_ADSAmmclVczdlNZB5SUU1Hi-H8mGcoUaAkboEALw_wcB who can take care of all aspects of a build.
Having a home buried (or even partially buried) in the earth is not practical for all locations - places where flooding is common, for example, would be a terrible place to put a geo sheltered house. People have been building homes on stilts in bayou country for centuries. There aren't really any good stock photos that I could find to demonstrate this concept, so just bear with me: A proper house for flood prone areas should have its foundation pillars driven down to bedrock, should be made of such materials as to be capable of withstanding a blow from a truck traveling at 60 miles per hour without giving way, and extend above the historical high water mark for the site. In order to achieve similar thermal insulative properties to a geo sheltered home, modern technology has come up with some interesting alternative construction materials.
Foamed concrete, sometimes called 'aircrete' is not exactly new, per se, having been in use primarily for insulation since the 1920s .. but with some advances in chemistry, it is now possible to create more durable and uniform air pockets in the material. Modern air crete has a durability very close to regular concrete, but an insulating factor that is more than 14 times that of earth - put another way, a one foot thick air crete wall is as well insulated as being buried 14 feet underground (R 44, for anyone interested in R values). Not too shabby. The weight of aircrete per cubic foot varies depending on the mix, but it falls between 20-60 pounds per cubic foot .. compared to the specific gravity of water at just over 62 pounds per cubic foot, and yes, it floats! The material is fireproof, waterproof, and does not suffer insect damage either.
Having a home made of aircrete on stilts takes care of a couple of concerns, but it still lacks the ground temperature constant that a geo sheltered home would have. In order to get close to that ground temperature constant, a passive geothermal heat exchange system can be used. The picture above is a rough sketch for the concept that was on my daughter's short list of science fair projects - we wound up building an electric generator from scratch instead - that shows how a very simple system of subterranean coils can be used to cool air from the surface, and circulate the cooled air up into a building. The Long black stacks on the peak of the roof absorb solar energy as heat, causing the heated air to rise, creating a pressure differential within the building, which draws the air through the pipes. This uses the same physics as the cupolas on the roofs of wineries .. the chambers create air flow to pull carbon dioxide gas away from the fermentation vats to prevent workers from suffering from asphyxia.
The position of the buried coils for cooling air can be as shallow as ten feet below the surface, or as great as thirty feet .. the precise optimal depth is variable from site to site .. but this same concept presents another interesting possibility: Thermoelectricity. Anyone who has or has had a gas powered water heater or floor furnace has already seen this principle at work: a series of circuits composed of two dissimilar metals (such as iron and copper) generate a low voltage current when heat is applied to the junction of the two metals. That current is used to hold a solenoid switch open, allowing the gas to flow, but will close if the pilot light (which is supplying the heat) goes out .. part of the reason for keeping the flame going when lighting your pilot lights is to allow for the thermopile to heat up enough to keep the solenoid open. The difference in temperature between the stacks on the roof and the ground constant temperature could be utilized to generate a small amount of electricity, enough to supplement a solar or wind system, for example. I will be doing some more experimentation with this concept in the future.
So, if you are ready to become a high-tech caveman (or woman) or just want to know a little bit more about some of these topics, materials and construction designs, I'm going to drop a few links here for your further exploration and enjoyment:
For how-to videos on aircrete, building a foam generator, and other nifty stuff, try Honeydo Carpenter: https://www.youtube.com/c/HoneyDoCarpenter/videos
Interested in free-standing concrete dome construction? This guy has some interesting techniques. Aircrete Harry: https://www.youtube.com/user/Cncdesignwork
Want to hear about universal habitat design from a rocket scientist? Sure, we can do that at Galactic Gregs: https://www.youtube.com/channel/UCmigPwwtQbetT7aVa9ToRuA