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Author Topic:   Introduction To Geology
RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 250 of 294 (688070)
01-18-2013 8:30 PM
Reply to: Message 249 by Dr Adequate
01-18-2013 6:08 PM


Re: Tidal rhythmites and dating
* A mixed cycle. This can be seen in many locations on the west coast of America. In a mixed cycle, there are two high tides and two low tides per day, but one high tide is higher than the other, and one low tide is lower than the other.
At Victoria BC (Canada ... used to live there) the tides go through a cycle from two highs and two lows to one high high and one low low and back over a two week period. This is due in part to the geography affecting the tides coming around Vancouver Island in two directions.
Enjoy

we are limited in our ability to understand
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RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 252 of 294 (688291)
01-21-2013 5:26 PM
Reply to: Message 251 by Dr Adequate
01-20-2013 11:42 PM


Re: Fossils And Absolute Dating
Hi again Dr Adequate
But this means that we can now use the fossil species to date the sedimentary rocks in which it is found; ...
The typical creationist complaint is that this is circular reasoning: rocks to date the fossils that then date the rocks ...
... but it is not circular: the first rocks are dated by radiometric methods the second rocks are usually of a type that cannot be dated by radiometric methods, sedimentary rocks, which is where the fossils are found.
It's linear:
dated rocks → date range for fossils → date range for undated rocks
The layers can also be tracked across the countryside and sometimes found between date-able rocks.
... well-known species of ammonite, trilobite, foraminiferan, or whatever, the age of which is already known.
And diatoms among others.
Enjoy

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This message is a reply to:
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Replies to this message:
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RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 280 of 294 (697134)
04-21-2013 8:19 PM
Reply to: Message 266 by Dr Adequate
03-06-2013 1:32 AM


Re: Ice Cores
Excellent as usual.
Another visual of ice layers comes from South America:
Ice layers introduction on Age Correlations thread
quote:
Paleoclimatology | National Centers for Environmental Information (NCEI) (3)
quote:
...

(Slide 3) The Quelccaya cap terminates abruptly and spectacularly in a 55 m ice cliff. The annual accumulation layers clearly visible in the photograph are an average of .75 m thick. While snow can fall during any season on the altiplano, most of it (80-90%) arrives between the months of November and April. The distinct seasonality of precipitation at Quelccaya results in the deposition of the dry season dust bands seen in the ice cliff. ...
Note that they are talking about correlating layers with climate information provided by d18O. We'll also come across this in other measurement systems. This is the proportion of a "heavy" isotope of oxygen in the atmosphere (16O is "normal" weight oxygen)
see Oxygen-16 - Wikipedia (1)
and Oxygen-18 - Wikipedia (2)
While this series of layers only date back to ~500AD they are important for a couple of reasons: they show visible layers, and they allow calibration of the oxygen isotope ratio (d18O) as a measure of layers and of climate. These layers also show a period of sever weather that is known from history (the Little Ice A
And there is more about other ice layer data sources and how the atmosphere isotopes can then be used to estimate ages of deeper layers when they become hard to distinguish.
It saddens me to think that we may be losing the Greenland and Antarctic ice fields and the immense bank of data that has not yet been tapped.
Enjoy

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
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RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 288 of 294 (720195)
02-20-2014 7:10 PM
Reply to: Message 283 by Dr Adequate
02-20-2014 1:04 PM


Re: Wikibook
nothing on page 1 for historical geology from BING
but #1 for historical geology wikibook
Edited by RAZD, : bing

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

This message is a reply to:
 Message 283 by Dr Adequate, posted 02-20-2014 1:04 PM Dr Adequate has not replied

  
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