Dead Things In Rocks!
Posted in Science on | 3 minutes | 3 Comments →
Usually occurring in layers of sedimentary rock distributed around the world, a fossil is any geological imprint of a once-living life form and the study of fossils is known as paleontology.
Fossils can be found by deliberate searching but they are often discovered as a result of industrial mining, development, natural disasters or weathering. A specimen need not die to leave a fossil, but the best fossils occur when a specimen is buried alive or rapidly after death as in land-slides, tar-pits, volcanic catastrophe and river-bank sediments. This process can occur in land, water or even amber, a hardened form of tree sap, often resulting in unaltered preservation. Water-dwelling creatures comprise the most common fossils, and natural mineral growths are occasionally mistaken as fossilized organisms.
The most common types of fossils are impressions and casts. An impression is any imprint of any organism initially made in soft sediments; a cast occurs when an organism’s hard parts are preserved in rock and subsequently washed out, leaving a cavity that may later be filled with hard minerals.
Although the chemical process of fossilization is rather simple, the particular conditions necessary for this process to occur are accordingly rare, and any given specimen will only fossilize under scant, fixed circumstances. Scientists estimate that archaeopteryx once thrived in a population of 1 million; the number of known extant archaeopteryx fossils is under ten. Intact fossilized bones are rare; full skeletons much more so. If a specimen is not buried rapidly after death, it is usually destroyed by scavengers. Specimens lucky enough to remain intact a few years after death will leach carbon, calcium and other minerals over time, and eventually turn to dust. Arid environments will retard natural decomposition, while acidic environments typical of tropical regions will expedite the decay process.
Museum reconstructions of dinosaurs typically contain very little genuine fossil remains. In the cases where we are lucky enough to have a full skeletal form, fossils can show us the general shape of an organism and reveal details about its skeletal structure, however, it is important to note that in most cases of fossilization, records of any internal structure are seldom discernible.
Additionally, sediments containing fossil specimens must not shift; even light tremors and other tectonic activity can disturb the fossilization process. Natural forces beneath Earth’s surface often twist, bend or bury sedimentary layers, even pushing parts of the sea floor into mountain ranges in a process of recycling carbon dioxide. Fossils usually will not preserve in sediment subjected to extremes in heat or pressure, such as those required to convert sedimentary rock into metamorphic rock.
Provided a specimen is rapidly buried under a sufficient amount of sediment, the resulting pressure typically expels water from that sediment, which will then convert into rock. Water flow through a rock containing a specimen can cause its organic elements to leach out and the specimen will convert into soft minerals, which are gradually replaced by hard minerals such as pyrite, silica, quartz, aragonite, or calcite. This process of remineralization can also reverse itself under certain circumstances, and the road that a living, breathing organism must travel to become a fossil is full of challenges!
Chet
says...Just wanted to pop by and let you know – “thalamus”, the singular, does actually refer to both lobes of the gland.
A single normal individual has only one thalamus; their single thalamus contains two major subparts.
That’s according to every standard usage in the literature.
cl
says...Chet,
What does it say about the meat in your arguments if they’ve been downgraded to banter over mere tense of a word?
Interesting that you’d slink over here telling me you were right when I wasn’t even wrong in the first place. You were unreasonably rude and condescending right off the bat on the other thread, even when I expressed that I agreed with your overall points as stated to John D, and even after our first little ditty which I thought was positive. You insulted me with ad hominems simply because you couldn’t wrap your head around my argument, and that’s a bona fide cheapshot in an ostensibly rational debate.
With that out of the way..
Yes, a thalamus contains two major thalami. The terms are interchangeable and so I was not in error to use the plural, but somehow I doubt you’ll agree or apologize.
Chet has spoken so we can rest assured, and there you go with your out-of-scope quantifiers again. Admitting my use of the plural thalami was correct would be much easier and courteous than trying to justify something I already know to be false, namely that zero eminent individuals in the field use the plural thalami. There’s so much reading I could suggest to you on this point, starting with Hillman.
Now if you want to tackle some real questions, get on any of my threads discussing AGITM and try again.
Or, take this one you left hanging:
“Technically, the thalamic nuclei show strong and reciprocal affiliations with the cerebral cortex, forming thalamo-cortico-thalamic circuits that are believed to be involved with consciousness, so I opine its absence is relevant, but feel free to state your counterpoint.”
Or any of these:
“My argument is that line-point mechanisms are not absolutely extensible. Surgical incisions and electrode stimulation merely alter circuitry and do not post hoc establish the origin of emotion in any spatial place. How would you respond to Spiegel, Wycis, et al. in their conclusion that “..it is not possible to refer emotional reactions to a single circumscribed nucleus within the diencephalon or to connections with the frontal lobes, but there exists a multiple representation of this function?” How do you reply to Grinker’s strong symposium against the absolute extendability of line-point mechanisms? How does the argument from mind-brain unity square with the well-documented tonsillectomy studies of the Italian brothers Calderelli showing that the emotions and personalities of tonsillectomy patients were noticeably and predictably affected, not by direct perturbations of brain matter but a commonplace medical procedure? If all emotion and personality resides in the brain, how is it that tonsillectomies produce similar effects? How do you respond to Shewmon, Holmes, and Byrne that kids and teenagers with congenital brain malformations involving the complete or near-complete absence of cerebral cortex curiously retain discriminative awareness, including but not limited to functional vision, distinguishing familiar people and environments from unfamiliar ones, social interaction, orienting, musical preferences, appropriate affective responses, and associative learning?”
gwp
says...I just received your feed blitz update and I am constantly enamored by your diarrhea geyser of knowledge which flows out of your mind. I am not trying to argue your points this is just another backhanded compliment in a style that I learned from you.