Real Science Radio's List of Missing Fossils

[gcthomas]

These are finger bones. What does that have to do with their feet?

The perpendicular 'distal' and 'dorsal' labels indicate that they are indeed foot bones, not hand bones, and that the curvature was related to grasping feet for climbing.

 

[gcthomas]

Maybe, but wouldn't that leave just as much of an error bar around the date of any sample? Including the ones taken at Laetoli?

The error bars of a fixed size will be a smaller fraction of an old date than for a young date. The date ratio of 3.6 million years to 6 years reduces the relative size of error bars by a similar proportion.

 

[One Eyed Jack]

Okay, if it can't be used on young samples, then how can it be reliably used on samples you don't know the age of to begin with? You have to assume they're old to get acceptable results. That's just a more elaborate form of circular reasoning.

 

[One Eyed Jack]

The perpendicular 'distal' and 'dorsal' labels indicate that they are indeed foot bones, not hand bones,

Hand bones don't have distal and dorsal positions? In any case, the picture's called finger_compare.gif.

and that the curvature was related to grasping feet for climbing.

Do the Laetoli footprints look like they were made by grasping feet to you?

 

[gcthomas]

Hand bones don't have distal and dorsal positions? In any case, the picture's called finger_compare.gif.



Do the Laetoli footprints look like they were made by grasping feet to you?

Google image search the image, and you'll see the text accompanying the image on a couple of sites. Read a few.

 

[gcthomas]

Okay, if it can't be used on young samples, then how can it be reliably used on samples you don't know the age of to begin with? You have to assume they're old to get acceptable results. That's just a more elaborate form of circular reasoning.

Really?

Because the signal to noise ratio is to small for young smokers, but much bigger for old samples. (this is the same as my earlier error bars discussion that you have ignored)

 

[One Eyed Jack]

Google image search the image, and you'll see the text accompanying the image on a couple of sites. Read a few.

Okay, but that's an odd name to give the picture, given that fingers belong on hands. I guess you could argue that ape feet are essentially hands.

I still want to know if you think the Laetoli footprints look like they were made by grasping feet. Do you have an opinion on that?

 

[One Eyed Jack]

Really?

Because the signal to noise ratio is to small for young smokers, but much bigger for old samples. (this is the same as my earlier error bars discussion that you have ignored)

Earlier you were saying a young sample would have a 'huge' error bar. Now you're saying it would be small? What kind of error bar does that make for the older samples -- mega-huge?

And again, how do you know they're older before you perform any dating tests on them? You have to assume they're old to accept the results you get. It's like institutionalized confirmation bias.

 

[One Eyed Jack]

The error bars of a fixed size will be a smaller fraction of an old date than for a young date. The date ratio of 3.6 million years to 6 years reduces the relative size of error bars by a similar proportion.

Okay, so what's the error bar for K-Ar? We'll go with the assumption that anything younger than this margin of error is untestable. So how do you determine whether or not a sample is old enough to test to begin with?

 

[gcthomas]

Okay, so what's the error bar for K-Ar? We'll go with the assumption that anything younger than this margin of error is untestable. So how do you determine whether or not a sample is old enough to test to begin with?

If the sample has enough Ar to measure reliably above the experimental noise, then it is old enough. The older a sample is the more Ar is produced from the K. There does not need to be a predetermination of the age, but the samples discussed of 6 year old material were always going to have indeterminate ages from K-Ar dating, especially when suitable precautions were not taken to avoid (such as not sampling minerals that wouldn't have had their 'clocks' reset by the eruption process.)

 

[Daedalean's_Sun]

Actually, he classified both as primates, but I'm not going to get sidetracked arguing about this.

Fair enough

We know their feet are shaped like this, because they left footprints like this, because their feet are shaped like this? That's circular reasoning. They could have been left by humans for all you know.

Firstly, we have a good idea of what their feet were shaped like because of fossil evidence. Not just foot bones, mind you, but their entire anatomy from the hands, to the hips, to the legs, are a testament to their method of locomotion.

Matter of fact austrolopithecine fossils were found in the same layer nearby.

I know, I know -- they've been radiometrically dated at 3.6 to 3.8 million years old.

Not just that, but regardless of what absolute age you want to assign to the formation, human remains have never been found in these stratum.

K-Ar. But this same method arrived at similar dates for ash (from Mt. St. Helens) that was known to be less than 30 years old.

Let's begin with a basic understanding of the radiometric dating technique used, K-Ar, or potassium-argon. This dating technique depends on the fact that the radioactive isotope of potassium, 40K, naturally decays into other elements, as do all unstable radioactive elements. There are two ways that this happens to 40K. About 89 percent of the time, a neutron inside the 40K undergoes beta decay, in which the neutron decays into a proton and an electron. This gain of a proton turns the potassium into calcium. But about 11 percent of the time, an extra proton inside the 40K captures one of its electrons and merges with it, turning the proton into a neutron and a neutrino, and converting the potassium into argon. ... However, all of these numbers are probabilities, not absolutes. You need to have a statistically meaningful amount of argon before your result would be considered significant. Below about 10,000 years, potassium-argon results are not significant; there's not yet enough argon created. The 11% of the time that potassium decays into argon and not calcium is also a probability, so this contributes to the result having a known margin of error. In addition, the initial amount of 40K that you started with is never measured directly; instead, it is assumed to always be .0117% of the total potassium present, which is the known distribution in nature. This has a standard deviation, so it also contributes to the margin of error. So when my result says the sample was 2.4 billion years old, this is only correct if the sample was at least 10,000 years old to begin with, and it's only correct plus or minus a calculated margin of error, in this example about 600,000 years. The bell curve of probable age starts at about 1.8 billion years, peaks at 2.4 billion, and dips back to the baseline at 3 billion. So whether you call it an exact science or not is a matter of linguistics. Although the exact age can't be known, the probabilities can be exactly calculated. Since Dr. Austin's sample was known to have solidified in 1986, its argon content was clearly well below the threshhold where an amount of argon sufficiently useful for dating could have been present.[/quote] source^ So, really, how do you know some couple and their kid didn't make them while taking a stroll through the area sometime after the last volcanic eruption? See above. I think without the rest of the foot bones, you'd hard-pressed to guarantee their arrangement in this way. There are rarely any guarantees in science, but the available evidence is indicative of what we see here. What kind of feet was A. sediba supposed to have? http://en.wikipedia.org/wiki/File:Australopithecus_sediba_and_Lucy.jpg According to this picture (I can't post the image for some reason), they, as well as Lucy, had pretty standard looking ape-feet. We're talking about morphological gradations in anthropology. This is as asinine as stating "they look like rocks to me" in a discussion about geology. Of course they're ape feet, but we're discussing to what degree they deviate from existing non-human apes in regards to locomotive morphology.