How Old was Nutcracker Man?
Best current Estimate: 1.75 million years old
Previous Estimate: 600,000 years old
Methods Used: relative dating, K-Ar Dating, Fission Track Dating, and Amino Acid Racemization
Initial Relative Dating
When Nutcracker man was discovered in 1959, he was believed to be the “world’s earliest man” (Leakey and Leakey). Louis and Mary Leakey, the scientists who found him, used relative dating techniques to hypothesize that he was 600,000 years old– at least 100,000 years older than the oldest previously discovered hominin(Leakey and Leakey). They used pre-historic animal bones that were found in the same stratum or soil layer as Nutcracker Man to place him at the lower end of the Pleistocence (Simons; Leakey and Leakey). They used the bones of (Leakey and Leakey):
- Afrochoerus: a gigantic pig with large tusks
Afrochoerus (image from ShukerNature) - Pelorovis: what Leakey describes as a large “pre-historic sheep”, but is now understood to be an ancient African cow
Pelorovis (image from deviantart.com) - And other pre-historic animals found with Nutcracker Man
to show that Nutcracker Man was alive around the same time these animals -which (in 1959) was believed to be 600,000 years ago (Leakey and Leakey).
Absolute Dating
Potassium-Argon Dating:
Everden and Curtis (image from UCBerkley)
Shortly after the Leakeys published their results, two geochemists-Jack Everden and Garniss Curtis- proposed a new age for Nutcracker Man- 1.75 million years old (Dunsworth). They used a new technique they had designed themselves, potassium-argon dating, to date the soil surrounding Nutcracker Man’s skull (Intro). This was the first time K-Ar dating had ever been used and their estimate (almost 3 times older than Leakey’s) shocked paleoanthropologists (Jurmain et al).
This type of dating was possible because the Olduvai Gorge is in the middle of the Great Rift Valley and was therefore subject to volcanic activity (Dunsworth). The extreme heat of a volcanic eruption eliminates all pre-existing argon from the rock, leaving only potassium (Dunsworth). The resulting ash (or tuff) that is laid down on earth’s surface has only potassium which will decay into argon at a predictable rate (Dunsworth). Scientists can then measure the tuff’s argon to give a date of when the volcanic eruption occurred(Dunsworth). Everden and Curtis tested several soil samples around Nutcracker Man’s skull, including:
- The soil immediately above and below Nutcracker Man’s horizon (soil level his skull was found within)
- Above: 1.89 million years old
- Below: 1.64 million years old
- The soil at a nearby site:
- Below NM’s horizon: 1.78 million years old
- The soil several miles away, but with comparable strata
- Above NM’s horizon: 1.74 million years old
- Below NM’s horizon: 1.63 million years old
and came to an average value of 1.75 million years old (Howell).
Controversy and Additional Dating Efforts:
This date was initially controversial for a couple of reasons (Howell):
- it was so much older than any other hominin estimates
- at the time, scientists believed the earliest hominins emerged only 1 million years ago
- Everden and Curtis sent their samples to two separate labs- one in California and one in Germany
- each lab came up with slightly different dates
- at the time, scientists feared their samples had been contaminated
- For example, the sample taken immediately below NM’s skull included some bone fragments within the tuff (could this skew the results?)
- Question of inherited argon (could argon have already been present at the time of crystallization/ soil formation?)
These initial concerns have subsided as K/Ar dating has become more commonplace. The results have also been corroborated by fission track dating (Fleischer et al). In 1965, three new scientists tested the same soil using this different technique (Fleischer et al). Using a subset of the same tuff (breaking it up and separating out the bits of porous glass), they dated the soil to 2.03 million years (+ or – .28 million years) (Fleischer et al). Taking the margin of error into account, this estimate aligns nicely with the initial 1.75 million year finding.
More recently (in 1987), amino acid racemization has also been applied to several bones and teeth found at Olduvai Gorge (Bada). Like radiocarbon dating, this is a direct method that instead of testing the soil surrounding the fossil, directly dates the fossils(Jurmain et al). It can be used to date items that are too old for carbon-dating techniques, although the researchers point out that the dates from earth’s oldest stratigraphic layers “should be viewed with caution and used only as minimum age estimates” (Bada). They found (Bada):
- Bottom of Bed I (NM’s soil layer): was at least 1.3 million years old
- Top of Bed I: was at least 1.2 million years old
These dates may not be as precise or useful, but do support what was already found.
Stratigraphy, Geology, and Context of Nutcracker Man
Olduvai Gorge is an open-air site in the middle of Africa’s Great Rift Valley. It is broken up into several different soil layers or “beds”. Nutcracker Man was found in the oldest layer, Bed I, 22 feet below its top boundary, at a spot later named FLK I (Leakey and Leakey). Bed I is roughly 40 feet deep and consists of alternating layers of tuff and lake sediment claystone (Hay).
Nutcracker Man’s Ecosystem
Today the site is dry gorge with several different bands of weathered soil clearly visible. But during Nutcracker Man’s time, the area looked very different. Using an understanding of the area’s history and information gleaned from the soil’s stratigraphy, Leakey hypothesized that Nutcracker Man died beside the shores of a lake- making Olduvai Gorge a fluvial site (Leakey and Leakey; Jurmain et al). Shortly after Nutcracker Man’s death, Leakey believed that the lake’s levels rose and fell, depositing soil over NM’s remains, fossilizing him for eternity (Leakey and Leakey). In the thousands of years between his death and discovery-earthquake activity, nearby volcanic eruptions and soil erosion shaped the landscape and soil stratigraphy into what we see today (Leakey and Leakey).
This initial hypothesis has been supported and enriched by more extensive geological work (Hay). Several teams of geologists have applied their techniques and understandings(including microscopic and x-ray scans of the soil) to the site (Hay). Some of these findings include (Hay):
- Evidence that identifies the Ngorongoro volcano as the volcano that erupted shortly after Nutcracker Man’s death
- it’s volcanic ash covered and helped preserve the artifacts and fossils below (including Nutcracker Man)
- Fossilized algae and mollucs were found within the soil of Bed I
- This suggests that the nearby lake occasionally flooded over during NM’s era (as Leakey originally proposed)
- Evidence that suggests that at the time of NM’s death, the lake was alkaline and strongly saline
- which may have implications on what animals/organisms survived in it
The Plant, Animal and Cultural Material Remains Found with Nutcracker Man
Several animal bones, primitive stone tools, and tool flakes were found in the same context as Nutcracker Man (Leakey and Leakey). This included “bird, snake, lizard, rodent, antelope and immature extinct pig” bones along with “Oldowan pebble tools” (Leakey and Leakey). The Leakeys initially hypothesized that the placement and state of the animal bones (most were broken and scattered about, while Nutcracker Man’s cranium was largely undisturbed) meant that site was hominin controlled and that the majority of the animals had been been consumed by Nutcracker Man and his tribe with help from the Oldowan tools (Leakey and Leakey). Since their hypothesis, several older hominin remains (including Homo habilis) have been found at the site, promoting further debate on when tool use and animal butchery first occurred in early humans(Jurmain et al). Because of the wealth of finds at Olduvai Gorge, a wide array of additional taphonomic research has been applied to the site throughout the years (Jurmain et al). The amount of research is overwhelming, but some highlights include:
- Phytolith analysis that shows Nutcracker Man’s environment was partially wooded and dominated by palm trees (Aramendi et al)
- Cut mark and scanning electron microscopy analysis on surrounding animal bones show that hominins (either Nutcracker Man or another species) were skilled butchers (Domínguez-Rodrigo et al)
- They were using stone tools on animal tissues (Potts and Shipman)
- Though it is difficult to determine which early humans were actually making and using the tools
Works Cited
Aramendi J, Uribelarrea D, Arriaza MC, Arraiz H, Barboni D, Yravedra J, Ortega MC, Gidna A, Mabulla A, Baquedano E, Domínguez-Rodrigo M. 2017. The paleoecology and taphonomy of AMK (Bed I, Olduvai Gorge) and its contributions to the understanding of the “Zinj” paleolandscape. Palaeography, Palaeoclimatology, Palaeoecology [Internet] 488:35–49. Available from: https://www.sciencedirect.com/science/article/pii/S0031018216308112
Bada J. 1985. Amino Acid Racemization Dating of Fossil Bones. Annual Review of Earth and Planetary Sciences 13:241–268.
Domínguez-Rodrigo M, Barba R, Egeland CP. 2007. Deconstructing Olduvai: A Taphonomic Study of the Bed 1 Sites. Springer.
Dunsworth HM. 2007. Human Origins 101. Westport, CT: Greenwood Press.
Fleischer RL, Leakey LSB, Price PB, Walker RM. 1965. Fission Track Dating of Bed I, Olduvai Gorge. Current Anthropology 6:389–390.
Hay RL. 1963. Stratigraphy of Beds I through IV, Olduvai Gorge, Tanganyika. Science 139:829–833.
Howell FC. 1962. Potassium-Argon Dating at Olduvai Gorge. Current Anthropology 3:306– 308.
Jurmain R, Kilgmore L, Trevathan W, Ciochon R. 2014. Introduction to Physical Anthropology. Belmont, CA: Cengage Learning.
Leakey M, Leakey LSB. 1960. Finding the World’s Earliest Man. National Geographic Magazine 118:144–160.
Potts R, Shipman P. 1981. Cutmarks Made by Stone Tools on Bones from Olduvai Gorge, Tanzania. Nature 291:577–580.
Simons EL. 1969. Reviewed Work: Doctor Leakey and the Dawn of Man . National Geographic Society, Encyclopaedia Britannica Educational Corporation. American Anthropologist 71:577–578.
