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They found a buried crystal cache. The sediment they were in dates to 105k years ago. I don't have access to the journal the actual paper is published in. Does

by seneca 6y ago

They found a buried crystal cache. The sediment they were in dates to 105k years ago. I don't have access to the journal the actual paper is published in. Does anyone know how they establish that they were gathered at that time and not just more recently buried? This article is light on details.

jph 6y ago
Article: We found 22 white and well-formed calcite crystals brought to the site 105,000 years ago. We determined this using a method called "optically stimulated luminescence", which dates sediments the crystals were excavated from. Our analysis indicates the crystals were not introduced into the deposits via natural processes, but rather represent a small cache of deliberately collected objects. See https://en.wikipedia.org/wiki/Optically_stimulated_luminescence https://en.wikipedia.org/wiki/Optically_stimulated_luminesce...
- seneca 6y ago
  Yes, I read the article. It specifically says the sediment was dated. I'm just curious how they're certain the placement of the crystals dates to the same time.
  - AlotOfReading 6y ago
    This dating method basically dates the last time the sediments were directly exposed to ionizing radiation (i.e. sunlight). The key here is that it sets a minimum age. Things can be older and have their "clocks reset", but the decay constant is fixed, so we can always determine the last time the object or sediment was exposed. There are a couple minor issues with it, but it's better (and sometimes cheaper!) than radioisotope dating. You can be pretty confident in OSL/TL dates more than a couple thousand years old.
Igelau 6y ago
Not an archaeologist, but if you're digging in a 105k year old sediment layer and none of the layers above it were disturbed, I'd say it's a pretty safe bet the stuff in it is also 105k years old.
- seneca 6y ago
  I suppose you must be right. I'm just wondering if there's some method they use to tell the difference between "this was left here 105k years ago" and "someone dug a hole here 50k years ago and buried them". Is it just as simple as "it doesn't look like it was ever dug up"? I have no clue how this stuff works.
  - klyrs 6y ago
    If you dig a hole, you puncture layers of sediment. Do it carefully, and you'll be able to see those layers of sediment on the walls of the hole. But the dirt you extract is mixed, and homogenized in the process. Fill in the hole, and the fill won't have nicely stratified layers. If somebody carefully digs in the same place 1000 years later, a cross section will reveal a homogeneous plug amid layers of strata. They'll be able to date when you dug the hole by looking at the layers above that homogeneous plug Fun thought: archaeologists 10k years from now unearthing today's digs, finding the traces of our careful destruction of ancient evidence...
- datavirtue 6y ago
  Archaeologists are very good at dating finds based on a range of different testing methods. In this case they used strata and an examination of the crystal's surface...at the very least.
adolph 6y ago
We excavated three areas of the shelter (4.75 m2 in total) and reached a maximum depth of 1.7 m, which revealed a sequence of stratified Middle Stone Age and Later Stone Age deposits Single-grain optically stimulated luminescence (OSL) dating of quartz from each of the three stratigraphic aggregates provided in-sequence dates with 1σ errors of 14.8 ± 0.8 ka (dark brown gravelly silt), 30.9 ± 1.8 ka (orange ashy silt) and 105.3 ± 3.7 ka (DBSR) (weighted mean, n = 3). Several lines of evidence provide support for an anthropogenic origin of the OES. First, the fragments occur within a well-preserved rockshelter context and are in direct association with many other traces of human activity (Extended Data Fig. 5). Second, the OES fragments show evidence of having been burned. Over 80% (n = 34) of the OES fragments display red colouration (Fig. 2, Supplementary Data), which reflects exposure to temperatures of 300–350 °C. Third, humans were the primary agents of accumulation for the faunal assemblage at GHN and there is no evidence for the presence of hyenas or other animals that consume ostrich eggs. The identifiable fraction of zooarchaeological material from the DBSR (n = 467) is dominated by remains of ungulates and tortoises (Table 1, Supplementary Data). Taphonomic analysis demonstrates a high frequency of anthropogenic percussion marks and cut marks (Table 1), and most of the faunal specimens show evidence of moderate burning.
- seneca 6y ago
  Thanks for the further info.

by seneca 6y ago

jph 6y ago

Article: We found 22 white and well-formed calcite crystals brought to the site 105,000 years ago. We determined this using a method called "optically stimulated luminescence", which dates sediments the crystals were excavated from. Our analysis indicates the crystals were not introduced into the deposits via natural processes, but rather represent a small cache of deliberately collected objects. See https://en.wikipedia.org/wiki/Optically_stimulated_luminescence https://en.wikipedia.org/wiki/Optically_stimulated_luminesce...

seneca 6y ago
Yes, I read the article. It specifically says the sediment was dated. I'm just curious how they're certain the placement of the crystals dates to the same time.
- AlotOfReading 6y ago
  This dating method basically dates the last time the sediments were directly exposed to ionizing radiation (i.e. sunlight). The key here is that it sets a minimum age. Things can be older and have their "clocks reset", but the decay constant is fixed, so we can always determine the last time the object or sediment was exposed. There are a couple minor issues with it, but it's better (and sometimes cheaper!) than radioisotope dating. You can be pretty confident in OSL/TL dates more than a couple thousand years old.

Igelau 6y ago

Not an archaeologist, but if you're digging in a 105k year old sediment layer and none of the layers above it were disturbed, I'd say it's a pretty safe bet the stuff in it is also 105k years old.

seneca 6y ago
I suppose you must be right. I'm just wondering if there's some method they use to tell the difference between "this was left here 105k years ago" and "someone dug a hole here 50k years ago and buried them". Is it just as simple as "it doesn't look like it was ever dug up"? I have no clue how this stuff works.
- klyrs 6y ago
  If you dig a hole, you puncture layers of sediment. Do it carefully, and you'll be able to see those layers of sediment on the walls of the hole. But the dirt you extract is mixed, and homogenized in the process. Fill in the hole, and the fill won't have nicely stratified layers. If somebody carefully digs in the same place 1000 years later, a cross section will reveal a homogeneous plug amid layers of strata. They'll be able to date when you dug the hole by looking at the layers above that homogeneous plug Fun thought: archaeologists 10k years from now unearthing today's digs, finding the traces of our careful destruction of ancient evidence...
datavirtue 6y ago
Archaeologists are very good at dating finds based on a range of different testing methods. In this case they used strata and an examination of the crystal's surface...at the very least.

adolph 6y ago

We excavated three areas of the shelter (4.75 m2 in total) and reached a maximum depth of 1.7 m, which revealed a sequence of stratified Middle Stone Age and Later Stone Age deposits Single-grain optically stimulated luminescence (OSL) dating of quartz from each of the three stratigraphic aggregates provided in-sequence dates with 1σ errors of 14.8 ± 0.8 ka (dark brown gravelly silt), 30.9 ± 1.8 ka (orange ashy silt) and 105.3 ± 3.7 ka (DBSR) (weighted mean, n = 3). Several lines of evidence provide support for an anthropogenic origin of the OES. First, the fragments occur within a well-preserved rockshelter context and are in direct association with many other traces of human activity (Extended Data Fig. 5). Second, the OES fragments show evidence of having been burned. Over 80% (n = 34) of the OES fragments display red colouration (Fig. 2, Supplementary Data), which reflects exposure to temperatures of 300–350 °C. Third, humans were the primary agents of accumulation for the faunal assemblage at GHN and there is no evidence for the presence of hyenas or other animals that consume ostrich eggs. The identifiable fraction of zooarchaeological material from the DBSR (n = 467) is dominated by remains of ungulates and tortoises (Table 1, Supplementary Data). Taphonomic analysis demonstrates a high frequency of anthropogenic percussion marks and cut marks (Table 1), and most of the faunal specimens show evidence of moderate burning.

seneca 6y ago
Thanks for the further info.