Even Older Fossils

You may recall that 2017 was the year that the conventional timeline for human evolution and migration finally toppled thanks to overwhelming archaeological and paleogenetic evidence. Our species is much older, and left its ancestral continent of Africa much earlier, than we previously thought. But a month after leading paleoanthropologists formally called for a rewrite of the timeline for humans leaving Africa, a stunning find in Israel pushes the revised date back even further. … Today, a partial jawbone from Misliya Cave in Israel joins those other early fossils outside Africa — and this new find is a lot [emphasis theirs] older.

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Known as Misliya-1, the partial maxilla, with several teeth preserved in situ, is 177,000 to 194,000 years old. That date range was determined by three different dating methods: uranium-thorium, combined uranium series and electron spin resonance. Tools found nearby (more on them below) were found to be approxiately [sic] the same age using thermoluminescence.

That date range makes Misliya-1 the oldest human fossils outside Africa as well as a contemporary of the humans found at Herto and Omo Kibish in Ethiopia. The Ethiopian fossils, however, like the even older Jebel Irhoud individuals from Morocco, exhibited some primitive traits. Crucially, all of Misliya-1’s features fall within the range of anatomically modern humans, and none of the traits resemble those of Neanderthals or other archaic humans. ¹

Most paleoanthropologists now agree on this new start date for our species in Africa (though a small number of researchers argue that humans evolved outside of Africa). But there is still a considerable amount of disagreement in the field about when anatomically modern humans left the continent and spread across Eurasia. For decades, conventional thinking set the date of our first exodus between 40,000 and 60,000 years ago. ²

There is disagreement about which Homo species count as human (just as some paleoanthro types disagree whether certain individual hominins in the fossil record represent discrete species or are merely different populations of a single species). In common usage, unless otherwise specified, the term “human” on its own refers to anatomically modern humans. You know, us. ³

Three independent numerical dating methods— U-series (U-Th), combined uranium series and electron spin resonance (US-ESR) series, and thermoluminescence (TL)—carried out in three different dating laboratories yielded consistent results (Fig. 2B [below], figs. S2 and S3, and tables S1 and S3). ⁵

The results of the 7 crust samples (one could not be dated) taken from the maxilla yielded (corrected) ages ranging from 19.4±2.5 ky to 185 ± 8.0 ky. Nevertheless, the dates are not randomly distributed along this time-range but rather are grouped: young dates 19-24 ky (2 samples), intermediate dates 45-70 ky (4 samples) and an old date 185.0 ky (1 sample). Similar distribution of dates was obtained for the 11 crust (2 failed to yield results) removed from animal bones and tools: 15-30 ky (6 samples), 50-60 ky (2 samples), >170 ky (2 samples). ⁶

In summary, the remarkable consistency of the dating results deriving from independent methods (carried out in three different independent laboratories) indicates the robustness of the chronological constraints of the Misliya-1 fossil. ⁷

Thermoluminescence can be used to date materials containing crystalline minerals to a specific heating event. This is useful for ceramics, as it determines the date of firing, as well as for lava, or even sediments that were exposed to substantial sunlight. These crystalline solids are constantly subjected to ionizing radiation from their environment, which causes some energized electrons to become trapped in defects in the molecular crystal structure. An input of energy, such as heat, is required to free these trapped electrons. The accumulation of trapped electrons, and the gaps left behind in the spaces they vacated, occurs at a measurable rate proportional to the radiation received from a specimen’s immediate environment. When a specimen is reheated, the trapped energy is released in the form of light (thermoluminescence) as the electrons escape. The amount of light produced is a specific and measurable phenomenon. If the specimen’s sensitivity to ionizing radiation is known, as is the annual influx of radiation experienced by the specimen, the released thermoluminescence can be translated into a specific amount of time since the formation of the crystal structure. Because this accumulation of trapped electrons begins with the formation of the crystal structure, thermoluminescence can date crystalline materials to their date of formation; for ceramics, this is the moment they are fired. The major source of error in establishing dates from thermoluminescence is a consequence of inaccurate measurements of the radiation acting on a specimen. The complex history of radioactive force on a sample can be difficult to estimate. However, thermoluminescence proven acceptable in providing approximate dates in the absence of more exact measures. ⁸

This finding changes our view on modern human dispersal and is consistent with recent genetic studies, which have posited the possibility of an earlier dispersal of Homo sapiens around 220,000 years ago. ⁹

All these dates, except for the U-series dating of the dentine, which exclude the possibility of recent intrusion, fall within the time range for the Early Levantine Mousterian lithic industry (TabunD-type) observed at Tabun, Hayonim, and Misliya caves … ¹⁰