|The Atom. . .the Nucleus|
History of Radioactivty
Hyper Physics Carbon-Dating
|Can We Prove That Carbon
Dates Are Accurate?
There are two ways to do this. We can date things for which historians know a "right answer". And, we can date things that have been dated by some other method.
Historians don't have "right answers" for really old things. However, carbon dating has done well on young material like the Dead Sea Scrolls, the Minoan ruins, and acacia wood from the tomb of the pharoah Zoser.
Some corals can be carbon dated, and also dated by another radioactive material, Thorium-230. Pollen found in the Greenland icecap has been carbon dated, and also dated by counting ice layers. The three methods confirm each other.
Trees grow a thick ring in a good year, and grow a thin ring in a bad year. It is sometimes possible to match up tree-ring patterns between different trees. When enough suitable trees are found, living or dead, the matching is completely accurate. Then, we have wood for which we know the right answer.
| So, carbon dating
has been calibrated against the rings of California bristlecone pines, and Irish
bog oaks, and the like. When this was first done, it turned out that carbon
dating had been giving too-young dates for early civilizations. Apparently,
the production of C14 by the Sun has changed by several percent across the last
10,000 years. We know (from other measurements) that the Sun hasn't fluctuated
by more than 10 percent in the last million years. However, even this small
an adjustment was a bit of a shock. For example, Stonehenge suddenly became
older than the Pyramids, instead of younger.
Since then, several other calibrations have been done, which confirm and extend the tree-ring one. Some were done by finding lakes with atmospherically derived carbon in their annual layers of silt (called varves ).
|Solar activity reaches new high|
|December 2, 2003
Geophysicists in Finland and Germany have calculated that the Sun is more magnetically active now than it has been for over a 1000 years. Ilya Usoskin and colleagues at the University of Oulu and the Max-Planck Institute for Aeronomy say that their technique - which relies on a radioactive dating technique - is the first direct quantitative reconstruction of solar activity based on physical, rather than statistical, models.
Sunspots are produced by magnetic activity inside the Sun. The more active the Sun is, the more spots are produced. Observations of sunspots began in 1610 - soon after the telescope was invented - and no other directly obtained data exists from before this time.
Now, Usoskin and co-workers have used the concentration of beryllium-10 in polar ice as a proxy for historic levels of solar activity. Beryllium-10 is produced when cosmic rays interact with particles in the Earth's atmosphere. The radioisotope then falls to the ground where it is stored in layers of ice. The Sun's magnetic field can deflect cosmic rays away from the Earth, so a stronger field should lead to less beryllium-10 being produced, and vice versa.
|Using modelling techniques, the Finnish team was
able to extend data on solar activity back to 850 AD. The researchers found
that there has been a sharp increase in the number of sunspots since the beginning
of the 20th century. They calculated that the average number was about 30 per
year between 850 and 1900, and then increased to 60 between 1900 and 1944, and
is now at its highest ever value of 76.
"We need to understand this unprecedented level of activity," Usoskin told PhysicsWeb . "Is it is a rare event that happens once a millennium - which means that the Sun will return to normal - or is it a new dynamic state that will keep solar activity levels high?" The Finnish-German team also speculates that increased solar activity may be having an effect on the Earth's climate, but more work is needed to clarify this.
|How can we find out how much C-14 is left?|
|Physics helps medicine gain a sharper view|
Positron Emission Tomography, or PET, is a procedure that allows a physician to examine the heart, brain, and other organs. PET images show the chemical functioning of an organ or tissue, unlike X-ray, CT, or MRI which show only body structure.
|Cog---our AI Friend|
is restricted to living things
. . .ones with brains sufficiently complex to allow them to draw fine perceptual distinctions, and to use them to select appropriate actions from an ample repertoire of behaviours.
. . .is the child of neural complexity
Contemporary physics and biology have sketched an ambitious account of our beginnings. It is, in a sense, our contemporary mythology, under-determined by the evidence, and doubtless incorrect in many details. Nevertheless it is the best cosmology to date, and has the great virtue that it is open to correction (modification) by new evidence.---Zeman
The elements of the nervous system - neuron, synapse, neurotransmitter and their receptors - are ancient indeed, originating in the common ancestors of multicellular organisms.
Which animals are conscious is much debated.
Encephalisation is associated with small broods, long lives, increasing biological intelligence, ever richer representations of the environment and increasingly flexible repertoires of response.
Simple nervous systems have no need of a 'perceptual code', while more complex nervous systems find it useful to develop conscious representations of objects organized in space and time.
These specific ideas are highly controversial, but they highlight the possibility that explaining consciousness may require a fundamental shake-up in physical theory.
Conventional explanations portray consciousness as an emergent property of classical computer-like activities in the brain's neural networks. The prevailing views among scientists in this camp are that
1) patterns of neural network activities correlate with mental states,
2) synchronous network oscillations in thalamus and cerebral cortex temporally bind information, and
3) consciousness emerges as a novel property of computational complexity among neurons.
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