Chapter 16
Radioactivity
Alpha
Beta
Gamma
Beta
Gamma
Carbon-14 Dating
Hyper Physics Carbon-Dating
ANSTO
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.
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 ).
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.
"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.
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.
Adam Zeman
. . .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.
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.
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.
Entanglement?
