Aide and Aide reported in 2012 that he rare earth elements (REEs) are commonly deï¬ned as lanthanum (La) and the 14 elements comprising the Lanthanide series. The REE’s typically exhibit trivalent oxidation states; however, Europium may also occur as Eu2+ and Cerium may occur as Ce4+. The REE’s ionic radii decrease on progression from La to Lu, which results in a slight but predictable change in their chemical affinity.
Typically,the light REE (La to Sm) reside in trace minerals such as apatite,epidote and allanite, whereas the heavy REE (Gd to Lu) are associated with minerals such as zircon. Investigations typically show that the REE are depleted in near-surface horizons and accumulate in deeper horizons or the regolith as clay-oxyhydroxide adsorbates or REE-phosphate precipitates. Numerous studies show the heavy REE accumulating in the deeper soil regions to a greater extent than the light REE, whereas other studies show the light REE’s preferentially accumulating at greater soil depths. The degree of interhorizon transport has great potential to become an index of weather intensity. The various REE soil migration pathways have been isolated, including lessivage (i.e., consists of a substantial vertical transfer of fine particles from an eluvial E-horizon to an illuvial B-11 horizon, a kind of leaching from clay particles being carried down in suspension. The process can lead to the breakdown of peds (the particles that give the soil its characteristic structure)), soil organic matter complexation, leaching in groundwater, adsorption by inorganic colloids, and precipitated by phosphate-bearing minerals.
Pathways for REE migration are numerous, involving (1) plant uptake, (2) erosion, (3) leaching of REE-inorganic complexes in percolating water, (4) organic complexation which may result in either mobilization or immobilization of the REEs, (5) lessivage (aka eluviation-illuviation of clay with coadsorbed REE’s, (6) removal o fREE’s from groundwater attributed to precipitation reactions, and (7) adsorption of REE’s by inorganic colloids (phyllosilicates and oxyhydroxides).
An important aspect of the REE’s is their similar soil chemistry; however, small differences in their hydrolysis and inorganic-organic complexation constants and inherent differences in the weathering susceptibility of the various REE-bearing minerals allow fractionation and differential migration potential. The real value of the REE’s to soil scientists lies in their ability to shed light on rates of elemental depletion and soil weathering intensities. If a greater understanding of the REE’s result in quantiï¬cation of soil processes; such as eluviation-illuviation, spodic horizon formation, erosion, elemental depletion because of leaching, oxyhydroxide formation, and hybridization, i.e., the term used in biology is defined as the process of halving the chromosomal content of a cell, creating a haploid cell. Within the normal reproductive cycle, haploidisation is one of the major functional consequences of meiosis, the other being a process of chromosomal crossover that mingles the genetic content of the parental chromosomes. Usually, haploidisation creates a monoploid cell from a diploid progenitor, or it can involve halving of a polyploid cell, for example to make a diploid potato plant from a tetraploid lineage of potato plants.
If haploidisation is not followed by fertilisation, the result is a haploid lineage of cells. For example, experimental haploidisation may be used to recover a strain of haploid Dictyostelium from a diploid strain. It sometimes occurs naturally in plants when meiotically reduced cells (usually egg cells) develop by parthenogenesis. Haploidisation was one of the procedures used by Japanese researchers to produce Kaguya, a fatherless mouse; two haploids were then combined to make the diploid mouse. Haploidisation commitment is a checkpoint in meiosis which follows the successful completion of premeiotic DNA replication and recombination commitment, according to Wikipedia at least.
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