Where is everybody? Don't tell me they've all been watching Kate & Wills ... WFL
FYI -- Below is a response I got back from an MIT earth sciences prof to my speculations on atmospheric loss due to K-T. I'm not convinced; we also used to think the continents didn't move, so why wouldn't the atmospheric composition be subject to changes? This prof is also ignoring the loss of a huge fraction of nitrogen on Earth relative to Venus. Re K-T event: we still aren't sure if it was one impact or a large number of impacts. If it was a large number of impacts of which the Yucatan crater is only the largest (and maybe not even the largest, if the largest crater were hidden in one of our oceans), then there could still be a lot of atmospheric stripping. "I think there is very little (no?) evidence that Earth's atmospheric pressure was higher in the last 100 Myr than it is today, dinosaurs notwithstanding. There is nothing but disagreement over atmospheric chemistry over Earth time. Venus' atmosphere is more massive because it is made of carbon compounds which are too massive to easily strip from the upper atmosphere, while Earth's carbon is sequestered as limestone rock thanks to our oceans. If all of Earth's limestone were vaporized we would be much like Venus." "Very large impacts like the Moon-forming impact are thought to be able to strip up to half the atmospheric mass of a dry planet, and more if the planet has oceans -- the ocean can deform far more and thus transmit forces to the atmosphere to accelerate it to escape. The K-T impact probably did not have anything like that effect, based on hydrocode impact modeling. It was just not big enough to create a big stripping event. there are a lot of people working on the effects of impacts, notably Sarah Stewart at Harvard, and this is not my main area of expertise."
On 4/29/2011 6:10 PM, Fred lunnon wrote:
Where is everybody?
Don't tell me they've all been watching Kate& Wills ...
WFL
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I have 0 interest in Kate & Willie. Here is a speculation on something nonmathematical. It often happens that we can't recall a word or someone's name but "know that we know" it. Consider the memory space taken up in two cases: 1. We recall the name with no problem. 2. We can't recall it, but it still takes up the same amount of memory, plus the space needed to realize we can't recall it. Brain economy would, I think, prefer the easier situation. So why does it ever happen that we know that we know it but can't recall it? Admittedly a very naive view, but this and other evidence convinces me that storing and retrieving are very different operations. Steve Gray
As we get older, we may lose some of the connections in our corpus collosum: http://en.wikipedia.org/wiki/Split-brain At 08:36 PM 4/29/2011, Stephen B. Gray wrote:
On 4/29/2011 6:10 PM, Fred lunnon wrote:
Where is everybody?
Don't tell me they've all been watching Kate& Wills ...
WFL
I have 0 interest in Kate & Willie.
Here is a speculation on something nonmathematical. It often happens that we can't recall a word or someone's name but "know that we know" it. Consider the memory space taken up in two cases: 1. We recall the name with no problem. 2. We can't recall it, but it still takes up the same amount of memory, plus the space needed to realize we can't recall it.
Brain economy would, I think, prefer the easier situation. So why does it ever happen that we know that we know it but can't recall it?
Admittedly a very naive view, but this and other evidence convinces me that storing and retrieving are very different operations.
Steve Gray
I just learned the other day that our brain constantly (?) prunes connections as we grow older. As a child, we have several orders of magnitude more synaptic connections than as an adult. I guess we could consider this as the brain optimizing. On Fri, Apr 29, 2011 at 10:32 PM, Henry Baker <hbaker1@pipeline.com> wrote:
As we get older, we may lose some of the connections in our corpus collosum:
http://en.wikipedia.org/wiki/Split-brain
At 08:36 PM 4/29/2011, Stephen B. Gray wrote:
On 4/29/2011 6:10 PM, Fred lunnon wrote:
Where is everybody?
Don't tell me they've all been watching Kate& Wills ...
WFL
I have 0 interest in Kate & Willie.
Here is a speculation on something nonmathematical. It often happens that we can't recall a word or someone's name but "know that we know" it. Consider the memory space taken up in two cases: 1. We recall the name with no problem. 2. We can't recall it, but it still takes up the same amount of memory, plus the space needed to realize we can't recall it.
Brain economy would, I think, prefer the easier situation. So why does it ever happen that we know that we know it but can't recall it?
Admittedly a very naive view, but this and other evidence convinces me that storing and retrieving are very different operations.
Steve Gray
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
Natural Compression/Decompression algorithms such that sometimes cross-referencing is accessible but specific data isn't ? On 30 Apr 2011, at 04:36, Stephen B. Gray wrote:
On 4/29/2011 6:10 PM, Fred lunnon wrote:
Where is everybody?
Don't tell me they've all been watching Kate& Wills ...
WFL
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
I have 0 interest in Kate & Willie.
Here is a speculation on something nonmathematical. It often happens that we can't recall a word or someone's name but "know that we know" it. Consider the memory space taken up in two cases: 1. We recall the name with no problem. 2. We can't recall it, but it still takes up the same amount of memory, plus the space needed to realize we can't recall it.
Brain economy would, I think, prefer the easier situation. So why does it ever happen that we know that we know it but can't recall it?
Admittedly a very naive view, but this and other evidence convinces me that storing and retrieving are very different operations.
Steve Gray
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
participants (5)
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David Makin -
Fred lunnon -
Henry Baker -
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Stephen B. Gray