The article points out that footprints in the 3.5 million years old range have been found, these are just the oldest footprints of Stone Age humans.
-- Only two things are infinite, the universe and human
stupidity, and I'm not sure about the former. (Einstein)
Re:Actually ...
by
reverseengineer
·
· Score: 3, Informative
Well, they're footprints of a recent precursor to modern humans, Homo heidelbergensis, which is believed to be the forerunner of both H. neanderthalensis and H. sapiens There are some paleoanthropologists, however, who think that H. heidelbergensis (I just love that name) might only be the direct ancestor of Neanderthals and that the break between H. neanderthalensis and H. sapiens occurred earlier.
It is also interesting to note that these footprints indicate that they were made by beings which were approximately 4.5ft (1.5m) tall, though H. heidelbergensis remains suggest that adults of the species may have been as tall as 6 feet (1.9m). Thus, as the article suggests, these footprints may have been made by children- or they made be from a completely different hominid species.
-- "FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
You can tell a lot from the footprints, such as the shape of pelvis bones, relative age and weight of the print maker, frequently the gender of the print-maker... all from the angle of the foot prints. If the prints are the correct proportions for 'human' and have the correct angles for a human walker, then scientists can probably narrow it down to being human prints with great accuracy.
-- The next Slashdot story will be ready soon, but subscribers can beat the rush and slashdot the links early!
Too bad Steve's been debunked
by
Anonymous Coward
·
· Score: 2, Informative
Re:How old are they?
by
Bowling+Moses
·
· Score: 2, Informative
I took a slightly extended lunch break today and went down to the university library to grab the original paper. There's some truly interesting things about your citing of Dalrymple. First off, you (or whoever your source is--in my experience creationists rarely read the original) didn't read the table right. The numbers that you present are actually the concentration of Ar-40 found in the sample, in 10^-12 mol Ar-40/g sample. The apparent age is in the third column of table 2 on page 51--I won't give them here (you'll have to look it up yourself) but they are much higher than the known age of the rock sample. However in the very first page of the article, Dalrymple states "The use of historic samples for these studies has two important advantages: (1) the ages of the flows are unambiguous, and (2) the material is so young that it is not necessary to make any correction for the 40Ar that is generated by the decay of 40K since the rock formed(emphasis mine)." The point of the study was a check of the methodology for K-Ar dating by looking at original levels of 40Ar present in the sample, not to date the rock sample itself. This is obvious--the half life of K-40 to Ar-40 is ~1.3 billion years so there should be very little Ar-40 in the sample produced by radioactive decay, which is exactly what we find. The most anomolously elevated level of Ar-40 is in the Hualalai sample, with 1.60x10^-12 mol Ar-40/g sample. In table 1 on page 50 we see that that the total amount of Ar-40 in this sample is 115x10^-12 moles, meaning that in this sample there is 1.4% more Ar-40 than is expected. What Dalrymple says about dating young rocks is this: "...anomalous 40Ar/36Ar ratios could be a problem in dating very young rocks. If the present data are representative, argon of slightly anomalous composition can be expected in approximately one out of three volcanic rocks (emphasis mine)." on page 52, meaning that the method would be inappropriate to apply to young samples--thus the USGS' 10,000-year limit (and I imagine the error bars here are still large). However as the rock grows older more Ar-40 will build up as K-40 decays. The more Ar-40 there is, the less that initial anomalous amount of Ar-40 will matter as its percentage of the total Ar-40 present in the rock drops--meaning that (to quote Dalrymple again on pg 52): "...the amounts of excess 40Ar and 36Ar found in the flows with anomalous 40Ar/36Ar ratios were too small to cause serious errors in potassium-argon dating of rocks a few million years old or older." (pg 52) ie. for old samples, the method is perfectly valid.
Slashdot Mirror
The article points out that footprints in the 3.5 million years old range have been found, these are just the oldest footprints of Stone Age humans.
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. (Einstein)
You can tell a lot from the footprints, such as the shape of pelvis bones, relative age and weight of the print maker, frequently the gender of the print-maker... all from the angle of the foot prints. If the prints are the correct proportions for 'human' and have the correct angles for a human walker, then scientists can probably narrow it down to being human prints with great accuracy.
The next Slashdot story will be ready soon, but subscribers can beat the rush and slashdot the links early!
Yawn. Look here troll.
I took a slightly extended lunch break today and went down to the university library to grab the original paper. There's some truly interesting things about your citing of Dalrymple. First off, you (or whoever your source is--in my experience creationists rarely read the original) didn't read the table right. The numbers that you present are actually the concentration of Ar-40 found in the sample, in 10^-12 mol Ar-40/g sample. The apparent age is in the third column of table 2 on page 51--I won't give them here (you'll have to look it up yourself) but they are much higher than the known age of the rock sample. However in the very first page of the article, Dalrymple states "The use of historic samples for these studies has two important advantages: (1) the ages of the flows are unambiguous, and (2) the material is so young that it is not necessary to make any correction for the 40Ar that is generated by the decay of 40K since the rock formed(emphasis mine)." The point of the study was a check of the methodology for K-Ar dating by looking at original levels of 40Ar present in the sample, not to date the rock sample itself. This is obvious--the half life of K-40 to Ar-40 is ~1.3 billion years so there should be very little Ar-40 in the sample produced by radioactive decay, which is exactly what we find. The most anomolously elevated level of Ar-40 is in the Hualalai sample, with 1.60x10^-12 mol Ar-40/g sample. In table 1 on page 50 we see that that the total amount of Ar-40 in this sample is 115x10^-12 moles, meaning that in this sample there is 1.4% more Ar-40 than is expected. What Dalrymple says about dating young rocks is this: "...anomalous 40Ar/36Ar ratios could be a problem in dating very young rocks. If the present data are representative, argon of slightly anomalous composition can be expected in approximately one out of three volcanic rocks (emphasis mine)." on page 52, meaning that the method would be inappropriate to apply to young samples--thus the USGS' 10,000-year limit (and I imagine the error bars here are still large). However as the rock grows older more Ar-40 will build up as K-40 decays. The more Ar-40 there is, the less that initial anomalous amount of Ar-40 will matter as its percentage of the total Ar-40 present in the rock drops--meaning that (to quote Dalrymple again on pg 52): "...the amounts of excess 40Ar and 36Ar found in the flows with anomalous 40Ar/36Ar ratios were too small to cause serious errors in potassium-argon dating of rocks a few million years old or older." (pg 52) ie. for old samples, the method is perfectly valid.