Between the lobe-finned fish tetrapods and the first amphibia and amniotes in the Middle Carboniferous lies a gap of 30 million years, with few satisfactory tetrapod fossils. This, noted in 1950, is Romer's gap. Some new fossils were found in the 1990s, such as "Pederpes", right in the middle of the Romer Gap. The gap still obscures the details of the tetrapod transition.
Sometime, in the later Devonian or earliest Carboniferous, the fishapods became mainly land-based. One group of them kept their link to the water, and always laid their eggs in water. They became the amphibians. The others evolved a way of laying eggs on land. They were the amniotes, whose key innovation was the cleidoic egg.
Sometime in the middle or lower Carboniferous, the amniotes split into two lines. One line lead to the reptiles of all kinds, and we call that the Sauropsida. The other line led eventually to the mammals, and we call that the Synapsida. It is not right to say "mammals evolved from reptiles" because both groups derived from early amniotes. In any event, modern reptiles are vastly different from modern mammals. Both groups have evolved for over 300 million years from the early amniotes.
Conservation status
The conservation status of a species shows how likely it is for that species to survive now or in the future. Many factors affect the conservation status of a species: the number remaining, the overall increase or decrease in the population over time, breeding success rates, known threats, and others.
Abstract algebra
Abstract algebra is a part of math which studies algebraic structures. These include:
It is normal to build a theory on one kind of structure, like group theory or category theory.
The purpose of the theory of each concept is to organize the precise definition of the concept, examples of it, its substructures, the ways to relate different examples of the concept algebraically (these are called morphisms in some cases), and the concept's applications, both inside its own theory and outside in other areas of mathematics.
During history, different fields of mathematics have used algebras. Algebras are about finding or specifying rules on how to calculate with certain mathematical formulas and expressions. Another algebra (which is not "abstract") is elementary algebra, for example.
Geodesic
In mathematics a geodesic is a curve with the shortest length between two places on a surface when considering places which are not "too far". These paths on a sphere are also called great circles, such that in this case, two points are joined by two distinct geodesics. A minimal geodesic (or segment) is a particular case where the geodesic joining two distant points has the shortest length.
Anarcho-syndicalism
Anarcho-syndicalism is a form of anarchism. It sees labour unions as something which will cause revolutionary change. This change will give freedom and equality to the workers. Anarcho-syndicalists want to get rid of the wage system and capitalism. They believe this leads to class divisions and inequality.
The basic concepts of anarcho-syndicalism are:
Anarcho-syndicalists believe that only direct action can bring about change. Anarcho-syndicalists do not take part in indirect action, like electing a representative to a government position.
Anarcho-syndicalism played an important role in the Spanish Civil War.
Trotskyism
Trotskyism is the form of communism that is based on the ideas of Leon Trotsky. Trotsky described himself as an "orthodox Marxist". This is a different way of seeing the ideas of Karl Marx than the way other communists like Mao Zedong and Joseph Stalin saw them. The biggest difference is in Trotsky's idea that there needs to be an international "permanent revolution". A permanent revolution is the idea that proletarian revolution needed to spread in countries worldwide, even where capitalism was not as advanced as only the proletarian revolution could carry out the tasks of the unfinished bourgeois revolutions in these countries. This is different to the Stalinist idea of trying to preserve a single nation's revolution from within. Trotsky also supported a less authoritarian government and more democracy.
The largest Trotskyist organizations today are the Reunified Fourth International, International Socialist Tendency, the International Communist League, and the Committee for a Workers' International.
A Fistful of Dollars
A Fistful of Dollars (1964) is a Spaghetti Western movie directed by Sergio Leone and starring Clint Eastwood. It is the first movie in the Dollars trilogy and was the first Spaghetti Western to be released in the United States. The second movie in the Dollars Trilogy is "For a Few Dollars More"; the third is "The Good, the Bad and the Ugly".
For a Few Dollars More
For a Few Dollars More (1965) is a Spaghetti Western movie directed by Sergio Leone and starring Clint Eastwood. It is the second movie in the Dollars trilogy and was released in the United States in 1967. The first movie in the trilogy is "A Fistful of Dollars"; the third is "The Good, the Bad and the Ugly".
The Good, the Bad and the Ugly
The Good, the Bad and the Ugly (1966) is a Spaghetti Western movie directed by Sergio Leone and starring Clint Eastwood. It is the third and final movie in the Dollars trilogy and was released in the United States in 1967. The first movie in the trilogy is "A Fistful of Dollars"; the second is "For a Few Dollars More".
This movie and "Once Upon a Time in the West" are considered to be the greatest western movies ever.
Ennio Morricone
Ennio Morricone (November 10, 1928 – July 6, 2020) was an Italian classical composer famous for making movie scores. He composed the scores for more than 500 movies and television programs. He is well known for composing the scores to , particularly Spaghetti Westerns.
In 2007 he received the Honorary Academy Award for his many great movie scores. In his career, the composer sold over 50 million records worldwide. In 2016, he won an Academy Award for his work on "The Hateful Eight".
Morricone was born in Rome. He died at a hospital in Rome on July 6, 2020 from problems caused by a fall, aged 91.
XTC
XTC was an English rock band. Its members were: Andy Partridge, Colin Moulding, Barry Andrews, and Terry Chambers. XTC started in 1976. They had their biggest success in the late 1970s and most of the 1980s. XTC was best known in their home country of England, but they had some fame in other countries like the United States. Their 2 biggest hits in the U.S. are "Dear God" and "The Mayor Of Simpleton". Some of XTC's other hit songs include "Making Plans For Nigel", "Senses Working Overtime", and "Are You Receiving Me".
XTC made a total of 13 studio albums. Their last album came out in 2000 and they broke up in 2005. Andy Partridge, the band's singer, says he doesn't think XTC will ever get back together.
One interesting thing about XTC is that they almost never did live concerts since 1982. The reason for that is because Andy Partridge sometimes got very nervous performing on stage in front of thousands of people.
Roh Moo-hyun
Roh Moo-Hyun is a former President of South Korea. He was born on August 6, 1946 in Gimhae, Gyeongsangnam-do, South Korea. He took office on February 25, 2003. After retirement from Cheongwadae, he was residing in Bongha Maeul, Gimhae, Gyeongsangnam-do until death. He committed suicide on May 23, 2009, by jumping off a cliff.
Kim Young-sam
Kim Young-sam (December 20, 1927 – November 22, 2015) was the President of the South Korea from February 25, 1993 to February 25, 1998. He was born in Geoje, South Gyeongsang. When elected in 1992, he became the first civilian to become president in over 30 years.
Kim died in a hospital in Seoul, South Korea from heart failure caused by a blood infection, aged 87.
Roh Tae-woo