The Jaramillo Subchron and the Domestication of Fire
Every now and again the Earth’s magnetic field flips, so that the + pole becomes - and vice versa [here].
A geomagnetic reversal is a change in the Earth’s magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth’s field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse polarity, in which the field was the opposite.
The geologic periods between polarity reversals are called chrons and subchrons [here].
Chrons are long periods during which the magnetic field remained oriented in one direction for most of the duration of the chron. The current chron, called the “Brunhes normal”, began 780,000 years ago. The immediate prior chron was the “Matuyama reverse”. … Most chrons are interrupted by shorter periods, called subchrons, during which the field flips to the opposite of the dominant orientation during the longer parent chron.
The Jaramillo Normal Subchron was a “normal” period of about 40,000 years from approximately 1.1 million years to 970,000 years ago [here].
Our mid-Pleistocene 40Ar/39Ar age recalibration of the geomagnetic polarity timescale is nearly in accord with the oxygen isotope, climate record calibration of the astronomical timescale proposed by Johnson (1982) and Shackleton et al. (1990). 40Ar/39Ar ages of a normally magnetized rhyolite dome in the Valles caldera, northern Mexico, yielded a weighted-mean age of 1.004 ± 0.019 Ma. A K-Ar age of 0.909 ± 0.019 Ma for this rock by Doell and Dalrymple (1966) was the linchpin for the recognition and calibration of the Jaramillo Normal Subchron (JNS). Other 40Ar/39Ar ages from the Valles caldera and 40Ar/39Ar ages of Ivory Coast tektites indicate that the JNS began at about 1.11 Ma and ended before 0.92 Ma, probably near 0.97 Ma.
Why is that important? Because depositions of iron-bearing sediments align with the Earth’s magnetic field and leave a permanent record of the polarity, known as post-depositional detrital remanent magnetization (pDRM) [here]. And those deposits can then be dated to within their particular chron or subchron.
In a recent paper [here]:
Francesco Berna, Paul Goldberg, Liora Kolska Horwitz, James Brink, Sharon Holt, Marion Bamford, and Michael Chazan (2012) Microstratigraphic evidence of in situ fire in the Acheulean strata of Wonderwerk Cave, Northern Cape province, South Africa.
researchers discovered burned bone fragments and ashed plant remains inside a cave, and dated the silty aggregates that enclosed them to the Jaramillo Subchron.
The ashed plant remains are situated in the middle of archaeological stratum 10, which shows a normal magnetic orientation and is bracketed between two cosmogenic burial ages of 1.27 ± 0.19 Ma and 0.98 ± 0.19 Ma. The Normal event can therefore be assigned to the Jaramillo subchron (1.07–0.99 Ma), a time range that fits with current understanding of the chronological position of the early Acheulean within the ESA [Earlier Stone Age] in Southern Africa.
The Acheulean is a cultural era or tradition typified by special types of worked tools [here].
[The Acheulean] was the dominant technology for the vast majority of human history starting more than one million years ago. Their distinctive oval and pear-shaped handaxes have been found over a wide area and some examples attained a very high level of sophistication suggesting that the roots of human art, economy and social organisation arose as a result of their development.
“They” being our ancestors, Homo erectus [here].
What does all this mean? It means that proto-humans were cooking with fire at least 1,000,000 years ago. The Abstract of the Berna et al paper:
The ability to control fire was a crucial turning point in human evolution, but the question when hominins first developed this ability still remains. Here we show that micromorphological and Fourier transform infrared microspectroscopy (mFTIR) analyses of intact sediments at the site of Wonderwerk Cave, Northern Cape province, South Africa, provide unambiguous evidence—in the form of burned bone and ashed plant remains—that burning took place in the cave during the early Acheulean occupation, approximately 1.0 Ma. To the best of our knowledge, this is the earliest secure evidence for burning in an archaeological context.
In Catching Fire: How Cooking Made Us Human [here] primatologist Richard Wrangham theorizes that Homo erectus was physiologically adapted to eating cooked food, and that adaptation dates to 1.8 million years ago. If proto-people could cook, if indeed cooking was a biological imperative, then ipso facto proto-people were capable of controlling fire.
And it follows that if our ancestors could cook with fire, they were certainly capable of setting fire to their environs.
Anthropogenic burning is a technology at least as old as Acheulean handaxes. Strong evidence from Wonderwerk Cave dates control of fire to 1,000,000 years ago, during the Jaramillo Subchron.
Hominids have been burning their landscapes for at least that long.
By the time the First People arrived in North America (15,000+ years ago), they had a million years of burning technology experience and practice under their belts.
If someday some fool questions you as to whether the Indians burned Oregon with skill and adroitness (as happened to me recently, by a college professor no less) you can tell him (as I did) that a million years of practice makes perfect.
by bear bait
We all become personally acquainted with our immediate environment, and go about ordering it to fit our particular needs. I would suppose that tendency is genetic/instinctive. We have been programmed by mutation and selection over the ages to hone that skill and purpose.
Of course fire is our domain. You don’t see any other critters packing matches or a zippo. We find all the time that other creatures use tools of one sort or another. Recently it was the bear using a rock to accomplish dermal abrasion to remove the detritus of hibernation. But not fire. That tool is ours alone.
The whole essence of survival is being able to either control or follow the environment that nourishes and promotes reproduction and long life. Fire is most important to our species. It allowed us to manage the environment, change the nutritional components of “food”, forge metals into tools, and protect our lives from wildfire, enemies, and diseases.
Of course we have used fire since we evolved. Yes it has been the most useful of our tools/skills. Apparently modern man has lost a lot of empirical knowledge of how fire is/was used in the past. The push to regain that knowledge and skill has been placed on Federal land managers, who seemingly can’t manage much other than self survival and cashing a paycheck. Academics are marginally better, if at all, as it appears they protect their livelihoods sort of like musk ox protect their young: circle up with all the weapons pointed out from their enclave of cloistered safety.