The Ediacaran period was previously called the Vendian period. The Vendian period was proposed in 1952 by Russian geologist/paleontologist Boris Sokolov. The term "Vendian" is still widely used.
The two terms are not the same. The Vendian was a longer period: it included the whole of the Marinoan glaciation, of Snowball Earth fame. In other words, the Vendian included the last part of the Cryogenian period.
The Ediacaran lasted for about 90 million years. It began at the end of the Cryogenian Snowball Earth. It ended with the first appearance worldwide of some kinds of trace fossils ("Trichophycus pedum") at the base of the Cambrian. The Ediacaran period's start is defined at the base of a carbonate layer, referred to as a "cap carbonate". This caps glacial deposits and shows a sudden climatic change at the end of the Marinoan ice age. The period ended with the mass extinction of almost all the Ediacaran fauna.
No exact dating has been possible at the type section of the Ediacaran period in South Australia.
The Ediacaran biota include the oldest definite multicellular organisms. The fossils are traces or impressions of soft-bodies forms with segments, fronds, disks, or bags. Skeletons or shells are not found.
Ediacaran biota
The Ediacaran biota are the fauna of the Ediacaran period. This geological period was from 635–542 million years ago, but the fossil biota was only from 575–542 million years ago. This was after a series of ice ages and just before the Cambrian period. The biota consists of soft-bodied multicellular organisms, probably animals, which left trace fossils in rocks of Ediacaran age.
The biota is quite unusual, and there is no sign of it in the preceding Marinoan glaciation. The biota appears to suffer a fairly severe extinction event at the boundary with the Cambrian. Some of the biota may have survived into the early Cambrian.
There have been several different interpretations of the biota. The standard view is that the traces are fossils of well-known phyla (Cnidaria, annelids, early arthropods) with body plans that disappeared before the Cambrian.
Quite different ideas have been put forward. Seilacher thought few if any of the forms belonged to living phyla. Conway Morris opposed this idea. Rentallak suggested the biota might be lichens.
As Narbonne explains, the Ediacaran biota occupies a critical position in the fossil record. Before them, for a long period of the Archaean and most of the Protoerozoic, the only fossils were those of bacteria and bacterial mats, a form of life which continues to the present day. The Ediacaran biota is found worldwide, and the most typical forms disappeared just before the Cambrian radiation, which begins with the 'small shelly fossils'. That is probably enough to justify the description of the change as an extinction event, though what caused it is not clear. One suggestion is that the evolution of animals which grazed upon the soft-bodied forms would have been sufficient to cause a collapse of the biota.
The biota was extremely varied, having many different body forms, and hence species. The ecology was benthic (sea bottom), in both shallow and deeper water. Narbonne notes the absence of different life and different depths, the apparent absence of burrowing organisms, and the absence of animals capable of preying on the soft-bodied forms. If these conditions changed, the soft forms would be in peril.
Ediacaran-type fossils are recognised globally in 25 localities, and a variety of depositional conditions, and are commonly grouped into three main types, named after typical localities. Each assemblage occupies its own habitat, and after a burst of diversification changes little for the rest of its existence.
In the White Sea region of Russia, all three assemblage types have been found close together. This, and the faunas' overlap in time, makes it unlikely that they represent evolutionary stages. Since they are found on all continents except Antarctica, geographical boundaries do not appear to be a factor. The same fossils are found at all palæolatitudes.
Probably the three assemblages mark organisms adapted to survival in different environments. An analysis of one of the White Sea fossil beds, where the layers cycle from continental seabed to inter-tidal to estuarine and back again a few times, found that a specific set of Ediacaran organisms was associated with each environment.
It is no surprise that not all environments are exploited. Of 92 possible modes of life — combinations of feeding style, tiering and motility — no more than a dozen are occupied by the end of the Ediacaran. Just four are represented in the Avalon assemblage. The lack of large-scale predation and vertical burrowing are perhaps the most significant factors limiting the ecological diversity; the emergence of these during the early Cambrian allowed the number of lifestyles occupied to rise to 30.
Antonio de Trueba
Antonio de Trueba (24 December 1821-10 March 1889) was a Spanish poet, novelist, and folklorist born at Montellana, Biscay, in 1821 (some sources say 1819), where he was privately educated.
Arrangement (music)
An arrangement of a musical composition is a reworking of a piece of music so that it can be played by a different instrument or combination of instruments from the original. For example, a song written for one voice with piano accompaniment might be arranged so that it can be sung in parts by a choir, or a piece for violin might be arranged so that it can be played on a clarinet instead. The person who does the arrangement may be the composer themself, or it may be someone else.
In music history, composers often published their compositions, saying that the music could be played or sung by various instruments. For example, when English composers published madrigals in the late 16th century they often stated that they could be sung by singers or played on viols (“apt for voices as for viols”). In the Classical music period a composer might publish a sonata, stating that it could be played on the violin or flute or recorder. This helped to sell more copies, because violinists, flautists and recorder players might all want to buy the music. In a sense this is not really an arrangement, because no changes have been made to the music.
However, when violin or cello music is arranged so that it can be played on a viola, some changes may be necessary as the viola may be playing in a different key, or some chords may be more awkward the way they were originally written. This is an arrangement.
A popular piece such as "The Flight of the Bumble Bee" by Rimsky-Korsakov can be played by almost any melodic instrument: violin, xylophone, tuba etc. These are all arrangements.
When a piece for choir and orchestra is printed for choir members to use, the orchestral part is printed on two staves so that it can be played on a piano for rehearsals. This is another kind of arrangement.
In music history, many composers have made arrangements of music composed by others. They did this in order to learn about musical composition, as well as in order to be able to play it on another instrument. For example, Johann Sebastian Bach made arrangements of four concertos by Vivaldi so that they could be played on the organ.
Arrangements are often made by people who play instruments that have not had much music written for them. People who play the viola, guitar, tuba etc. often arrange other music so that they have a larger repertoire (more music to play).
Sometimes composers have made changes to the orchestration of works for orchestra written by others. They may have done this because instruments had changed since the music was written, or simply because they thought they could do it better. For example, Mozart made an arrangement of Handels "Messiah ", adding instruments such as clarinets which Handel would not have known. Rimsky-Korsakov made arrangements of the operas by Musorgsky thinking that he was improving them.