Another important discrepancy between the whole mantle convection model and our observations is the lack of evidence for thin plumes, such as the one proposed to underlie Hawaii. This is of great concern to whole mantle convection proponents e. Importantly, a mechanism for plate tectonics is not described, and no heat source sufficient to drive mantle convection has been proven. These, other first-order problems described by Bercovici , and the issues set forth on www.
Our paper provides a new, pertinent, mathematical derivation of the Rayleigh number and a discussion of materials science literature. This webpage explains elementary, fundamental concepts. And yet the continental crust does not convect. Thus the Ra number of the lower mantle being large may not be sufficient evidence to demonstrate convection. What did Rayleigh assume?
The original derivation of Rayleigh was an attempt to characterize liquid behavior. This is hardly surprising as ships dominated transport at that time. Liquids behave differently from solids, as is taught very early in scientific education. One key difference is that solids melt when their internal temperature exceeds their melting point.
After this phase transition occurs, motions, including convective circulation, are easily stimulated. Rayleigh assumed that the motions of the medium were brought about by thermal buoyancy only. In contrast to liquids, solids must be significantly stressed to flow.
Liquids like water flow downhill with even the slightest tilt. The requirement of force to move solids is evident in the home during use of a garbage compactor.
Volume reduction is not the only change in a garbage compactor: the solids can also change shape, because the applied force is not uniform in all directions. Also, tough solids like a bone will not change shape, but softer things, e. Non-uniform force in scientific terms is called stress. How much stress is needed for deformation depends on the material. For example, munster cheese, a soft cheese, will deform at far lower stress than does a block of hard cheddar.
Importantly, deformation implies non-elastic behavior, where the solid does not return to its original shape after the stress is removed. More succinctly, above a certain stress the solid yields, but below a certain stress a solid responds elastically and reversibly. The mechanical behavior of cheese is discussed in terms of an activation energy by Kim et al.
Regarding convection of a solid, the material must be able to deformation and flow. Due to the great hardness and strength of rocks, the yield stress is necessary to describe their behavior. Furthermore, it is not volume reduction under hydrostatic conditions that is important, but the difference between the applied, directional forces and hydrostatic compression, i.
On this basis, our paper proposed that:. Deviatoric stress must exceed the yield stress of material for a solid to convect — 1. Our contention is supported by data and theory in materials science, such as the concept of an ideal Bingham plastic, and the large effect that grain-size has on deformation of solids e. Grain-size is irrelevant to liquids and to the Ra number.
Hence, a high value of Ra is no guarantee of convective instability of a solid system.
Deformation studies of rocks and mineral composites provide confirmation. Such conditions are outside the elastic regime see Figure 8 in our paper.
This conclusion is supported by seismic measurements, which provide data on the interior of the Earth from compression and shear waves induced by earthquakes, and by comparing the results to laboratory measurements of elastic properties e. Once stress is sufficiently high, a solid will move in a similar manner to a fluid. Under high stress conditions, rocks do deform.
Actually, the rocks creep. Brangwynne Nature , —; Each hypothesized that organic compounds underwent reactions leading to more complex molecules, and eventually to the first life forms. What was missing then, as now, is a concrete theory for the physics of what life is, testable against experiment — which is likely to be more universal than the chemistry of life on Earth.
Ball Nature , —; attempted to lay conceptual foundations for such a theory. Yet, more than 70 years and two generations of physicists later, researchers still ponder whether the answers lie in unknown physics. No one has led the charge on these questions quite like Stuart Kauffman. He posited that if a chemical soup of polymers was sufficiently diverse, these sets would emerge spontaneously as a phase transition — that is, a significant change in state or function, akin to the shift from solid to liquid.
The sets function holistically, mutually catalysing the formation of all their molecular members. Most atoms are simple, so all their possible states can exist over a reasonable period of time. Once they start interacting to form molecules, the number of possible states becomes mind-bogglingly massive. Only a tiny number of proteins that are modestly complex — say, amino acids long — have emerged over the entire history of the Universe.
Generating all 20 of the possibilities would take aeons. Given such limitations, how does what does exist ever come into being? This is where Kauffman expands on his autocatalytic-sets theory, introducing concepts such as closure, in which processes are linked so that each drives the next in a closed cycle. He posits that autocatalysing sets of RNA, peptides or both encapsulated in a sphere of lipid molecules could form self-reproducing protocells. And he speculates that these protocells could evolve. Thus, each new biological innovation begets a new functional niche fostering yet more innovation.
You cannot predict what will exist, he argues, because the function of everything biology generates will depend on what came before, and what other things exist now, with an ever-expanding set of what is possible next.
Jul 7, Anderson, Don L. () New Theory of the Earth. PDF (Front matter and table of contents) - Published Version PDF (Chapter 2. Buy New Theory of the Earth on huwataboqovo.tk ✓ FREE SHIPPING on qualified orders. New Theory of the Earth 2nd Edition. by.
This is the only book on the whole landscape of deep Earth processes that ties together all the strands of the subdisciplines. It includes dozens of new figures and tables. A novel referencing system using Googlets is introduced that allows immediate access to supplementary material via the internet.
There are new sections on tomography, self-organization, and new approaches to plate tectonics. As with the Theory of the Earth, this new edition will prove to be a stimulating textbook for advanced courses in geophysics, geochemistry, and planetary science, and a supplementary textbook on a wide range of other advanced Earth science courses.
It will also be an essential reference and resource for all researchers in the solid Earth sciences. Repository Staff Only: item control page. A Caltech Library Service.
New Theory of the Earth.