The Baked Earth and Cinders of the Miocene Pampas. Man made or natural?

In my recent post on the Diprothomo platensis, I mentioned among the evidence put forward by Argentine archaeologist and paleontologist Florentino Ameghino, the presence of "eoliths" (crude stone tools with an Oldowan appearance), and also, baked earth, which he attributed to the activity of hominins in the Miocene Pampas.

Today's post will look into the baked earth and the different theories about its origin, following, and expanding the interesting work by Pasquali and Tonni, 1998.

Original images of baked earth. Podgorny, 2015

There is a discontinuity in the sedimentary cliffs along the coast of Buenos Aires province, where, as a layer in the Cenozoic terrain there are chunks of spongy-like, dark rock-like fragments 3 to 10 cm in size (2.2 to 4 in), they are called escorias or slag, very similar to volcanic cinder and, accompanying them there are brick-like rocks, in different shapes and sizes which were named tierras cocids or baked earth. They seem to have been formed by applying intense heat to the soil.

Hearths

Florentino Ameghino suggested in 1881 in his work The antiquity of man in the Plata (see p. 240) that they were the outcome of cooking clay in a hearth, man made artifacts, and took them as proof the ancient presence of humans in the age of the megafauna (remains of extinct glyptodonts are found in this layer).

Ameghino asks what do the fragments of baked earth "indicate? Are they the products of the first experiments in ceramic art, or are they simply the result of the action of fire from a hearth lit by humans in the time of the Glyptodon? We believe that the latter supposition is the most plausible, since the humans who inhabited Europe during the later Quaternary period did not know the art of pottery. It would therefore require more than just goodwill to admit the existence of a potter contemporary with the Glyptodon."

Prairie Fire

Later, in 1907 he explained the origin of the baked earth by assuming that human beings deliberately set the dry grasses of the Pampa prairies alight, to make hidden prey escape, and hunt them. The fire spread quickly and the grass turned into ashes fast but the roots, below the surface kept on burning for days, causing the clay in ths soil to acquire a brick-like appearance.

But, Ales Hrdlicka, 1912 who came to Argentina to validate (actually to criticize and erase) Ameghino's theory of the Tertiary man, originating in South America, also studied the baked earth. Read the conclusions of Hrdlicka in his Early man in South America, 1912 Smithsonian Institution, Bureau of American Ethnology Bulletin which dedicates its Part. IV to the "Tierra Cocida, Scoriae" (p. 45-98).

Original caption reads: "fragments of 'baked earth' with Pampa grass slits (Cortaderia selloana) inside them. The handwritten label by Ameghino states "Lower Chapadmalense. Mouth of de las Brusquitas Creek. F. Ameghino, Septbr 5, 1908". (Ameghino Colection, MACN)". Source

A geologist in his team, Whitman Cross (p.47) conducted controlled burns and found no effect on the soil or subsoil. However, Bailey Willis, part of the same team, inspected a plot of land which had burned recently and found brick-like structures in the soil, and remarked (p. 48) that "There is nothing, however, to connect the burnt earths of the Pampean with man, so far as the occurrences were observed by the writer. Any fire whatever, whether originating in spontaneous combustion, in lightning, or in other natural conditions, independent of man, would have the effect of burning the earth under favorable conditions"

The samples were tested (see Part V, p. 88) and the results showed they had been subjected to temperatures ranging frmo 850°C to 1050°C. The cinders or escoria were found to be non-volcanic, these glassy particles were formed by the melting of certain minerals found in the loess of the Pampas at temperatures above 1050°C.

Much later, in 1971, Césear Cortalezzi proposed that the cinders were formed by chemical reactions in the soil, involving acidity and minerals in the loess.

Volcanic origin

Outes, Delachaux and Bücking had proposed in 1915 a volcanic origin: "General Conclusions. 1 The cellular-structured scoriaceous materials extracted from Monte Hermoso and other deposits are andesitic lava scoria. 2. The compact, red, brown, or grayish materials previously considered "fired earth" are mostly eruptive tuffs."

However, there are no volcanoes in the Pampas, the closest are in the Andes, in Neuquén and Mendoza and Neuquén provinces, over 860 km (530 mi.) west of Monte Hermoso (see the location of this site in Google maps).

The authors overcome this problem by citing Charles Darwin: "Numerous, small, well rounded pebbles of pumice lie scattered both on the plain and sand-hillocks: at Monte Hermoso, on the flat summit of a cliff, I found many of them at a height of 120 feet (angular measurement) above the level of the sea. These pumice pebbles, no doubt, were originally brought down from the Cordillera by the rivers which cross the continent, in the same way as the River Negro anciently brought down, and still brings down, pumice, and as the river Chupat brings down scoriæ: when once delivered at the mouth of a river, they would naturally have travelled along the coasts, and been cast up, during the elevation of the land, at different heights" (Source).

Meteor Impact

Another explanation published by Schulz et al., 1986, in Science (A 3.3-Ma Impact in Argentina and Possible Consequences) suggested an impact origin: a meteor hit the Earth around 3 million years ago. This team had previously studied the craters of a meteorite that struck the ground ~4000 years ago in Río Cuarto, Córdoba, Argentina and found the cinders similar to those found in the baked earths. They found a mineral formed by zircon dioxide which requires a temperature of 1700°C, which is far to high to be produced by burning grasses.

The dating of the cinders led Schulz to believe that a meteor struck the region close to Buenos Aires province 3.3 million years ago, and as there is no visible crater, they conjecture it impacted the now submerged continental shelf close to Miramar or Mar del Plata, in Buenos Aires province (see map below, from their paper). This event was catastrophic: "[the
age of the deposits coincide with a pulselike change in the deep-sea stable isotopic record, reflecting a sudden change in climate and ocean circulation. These coincidences suggest that the impact may have directly induced regional faunal extinctions or triggered broader environmental changes leading to ecosystem collapse in Argentina." If there were Tertiary humans in the area, they would have been wiped out.

Conclusion

Whether we believe or not in the Tertiary man proposed by Ameghino, or in an early peoping of America by non-Homo-sapiens people, the question of baked earth has puzzled scholars for over 140 years. The explanations are interesting, some more formal than others. My preference is the meteoric impact. I don't think that it has a volcanic origin, or that wildfires of prairie grasses caused the baked earth.

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Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2026 by Austin Whittall © 

The Diprothomo platensis

In a recent post, I mentioned the Diprothomo platensis, a hominin described by Florentino Ameghino (see his work online Le Diprothomo Platensis, (full title in French adds "A precursor of the Lower Pliocene man"), published in 1909 in Buenos Aires, in French.

I have mentioned this "hominin" in several posts over the years: Diprothomo and Lagoa Santa - Homo erectus? (2011) and more recently At the Buenos Aires Natural Sciences Museum (2025) where I got to see the skull.

Ameghino's book on the Diprothomo platensis

In his book he mentions how the upper part (calotte) of a skull was discovered during the construction of Buenos Aires' port, on the River Plate, at Dry Dock #1 on the north flank of the Darsena Norte (North Dock). Though built between 1887 and 1897, ths spot still exists even though the old port and docks have been recycled and revamped into a posh,expensive neighborhood (see Google map).

Ameghino stated that the skull came from the basal layer of the Pampean Formation of Pliocene age, 40 to 50 m thick (120 to 150 ft.), and that dips up to 20 m (60 ft) beneath the River Plate's water level. The lowest level was labeled "Pre-Ensenadan", 32 meters (66 feet) below ground surface.

Fig. 7. Diprothomo platensis seen from above, at natural size. The oval-shaped depression seen on the left side of the frontal bone is the imprint of an old wound

Ameghino also added two plates with top views of a Pithecanthropus (now known as Homo erectus) and and a Neanderthal, shown below.

He included a lateral view of it (below) and remarked about it being more primitive (inferior) than the (already inferior) Neanderthal: "The famous Neanderthal skull, whose inferior characteristics have been greatly exaggerated, differs profoundly in its lateral view from that of Diprothomme and by characteristics that indicate a much more advanced evolution than that of the latter."

Below is a front view of the skull cap and the browridges.

Ameghino provided a reconstruction of the complete skull, as he imagined it, a primitive, small-brained, low forehead, hominin with prominent brow ridges:

In the article, he fitted the Diprothomo into his evolutionary sequence for the first humans, originating in South America, and from there, expanding across the globe. Ameghino believed that humans had evolved during the Tertiary Period (see my posts on his theory). His phylogenetic tree, outside of America places the Diprothomo as an ancestor of both modern humans and the parallel branch of Neanderthals, and regarding the Pithecanthropus, he states they are different genra, and points out the lack of metopic crest in the Diprothomo (no mention of the saggital crest) adding: "These are two divergent morphological lines, the one that leads to Pithecanthropus is completely extinct. Based on the bestialization characteristics it presents, I declared in 1906 that Pithecanthropus was not and was the ancestor of Man." Below is Ameghino's phylogenetic tree:

Notice the progression from the Tetraprothomo to the Triprothomo (leading to the pithecanthropus or Homo erectus), diprothomo, prothomo, and the Homo pampaens, that leads to modern Homo sapiens!

The final part of the book includes some photographs of the skull.

But this theory, and the findings went against the dogma set down by the American (for U.S.A) school of thought that proposed the Beringian route for an Old World human to reach America relatively recently (3,000 to 10,000 years ago). This cause was championed by Czech - American anthropologist Alex Hrdlicka and his team. After visiting Argentina in 1910, and inspecting the bones (of Diprothomo and other specimens) they harshly refuted Ameghino’s theory, ridiculing it and effectively killing it (see a summary published in Science, 1912). Hrdlicka's legacy lives on in the Clovis First theory (see my post on it).

In 1912 Hrdlicka, Holmes and Bailey Willis published through the Bureau of Ethnology of the Smithsonian Institution a report, "Early Man in America". They say that the skull was not found embedded in the sediments, but that it probably fell down, into the excavation site of the dry dock from more recent sediments. That the workers had been playing "bochas" (bowls) with the skull (page 320). But, reading the arguments put forward to discredit the site, I am not fully convinced that they are impartial or that Ameghino was wrong.

Then, the authors state that Ameghino aligned the skull incorrectly, and this led him to conclude it had a small brain and slanting forehead: "In a detailed study of the specimen it soon became plain that almost the entire original description by Ameghino had miscarried by reason of the fragment having been placed and considered in a wrong position." Below is an image depicting the "correct" (upright - Hrdlicka) and the "incorrect" (slanting - Ameghino) positions for the calotte:

The American team concluded that "The sum of the results of the writer's study of the Buenos Aires skull fragment, regardless of its uncertain history, is that the specimen fails utterly to reveal any evidence which would justify its classification as a representative of a species of ancient Primates, premediate forerunners of the human being, the Diprothomo. Every feature shows it to be a portion of the skull of man himself; it bears no evidence even of having belonged to an early or physically primitive man, but to a well-developed and physically modern-like human individual" Categorical rebuttal of Ameghino's claims.

A Modern view on the Diprothomo

Schávelzon, 2018 argues that Ameghino's skull is recent, and was brought by the potent current of the Paraná River downstream, ending up in the sediments in Buenos Aires, he also states that it dates back to 1720, without providing a source.

Politis and Bonomo, 2011, review Ameghino's findings and theories, and regarding Diprothomo, they offers two explanations: the one given by Bailey Willis, or as a second option, a hoax; and they don't blame it on Ameghino but on the ones who discovered the skull perhaps with the intention of selling it, a common practice in those days.

The dating of the skull mentioned in both papers is unpublished, and Politis and Bonomo gives the following account: "In 1997, José Bonaparte, then director of the Vertebrate Paleontology Section of the Bernardino Rivadavia Museum of Natural Sciences, where the skullcap is currently housed, sent a sample of it to the University of California, Riverside laboratory for AMS dating. The age reported by Taylor on April 22, 1998, is 230 ± 40 14C years BP (Table 1). In the report, Taylor notes that the rest of the bone was in suitable condition for radiocarbon dating: “The analysis was taken on the total amino acid fraction by ion exchange chromatography after chemical and physical cleaning of the bone surface to remove any adhering contamination. The amino acid profile indicated that the bone still retained a considerable amount of collagen.”"

Conclusions

Despite his mistakes (earnest ones), which we can excuse due to the lack of adequate dating tools, other than sedimentary references, Ameghino may have been onto something.

Baked Earth

He also suggested that samples of "tierra cocida" or baked earth were primitive ceramics produced by these ancient hominins in their hearths during the Tertiary period. These chunks of clay similar to broken bricks caused quite an uproar during the early 1900s. (See Podgorny, 2015 who also gives a good summary on the Diprothomo). Ameghino also noted the presence of "eoliths" or very crude stone tools found in deep layers, which he believed were pre-Acheulean.

I will post about the Baked Earth in a coming article.

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Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2026 by Austin Whittall ©