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Guido 2006-02-28 17:26

Major extinction events that came before Hikari
Ever since I heard the term Seventh Extinction, I felt curiosity about the extinction events that rocked the Earth mya, and the aftermath that they brought on to it.

Mass extinctions generally happened at the end of a period in the Geological Time Scale within the same era, or a period marking the end of an era to delimit the boundary for the beginning of the next era.

Six major extinction events ocurred throughout the course of the Phanerozoic Eon (the current Eon when mankind is still ongoing).

An interesting note is that the previous eons- Proterozoic + Archaean= Cryptozoic- accounted an 85% of the Earth's geological lifetime history.

The Big Five
1. Ordovician-Silurian extinction event.
Recorded time event: 444 mya
Speculative cause that triggered this event was a super-extended Ice Age period, followed before it by a steady drop of carbon-dioxide in the atmosphere. The ongoing glaciation gave away to an unstability in the rising and dropping of the sea levels.
Irregular change patterns in the rise and drop of water in the world-ocean destroyed marine biodiversity.
Aftermath: A 49% of the world's total fauna was wiped out.
Extincted species: One hundred marine families decimated, including the brachiopods & bryozoans. Many trilobite, conodont, and graptolite families were decimated as well.
Ranking: Second catastrophic extinction the Earth faced.

2. Late Devonian extinction.
Recorded time event: 364 mya
Suggested causes that triggered this event maybe were: a) bolide meteors that impacted on the Earth, b) the "Greening" of the continents by blooming of land plants produced photosynthesizing that led to a sharp decline of atmospheric carbon-dioxide, or c) widespread glaciation.
Aftermath: A 75% of the world's total fauna was wiped out. Marine genera- particularly the invertebrates- were the most affected. Land species and plants were the least affected.
Extincted species: The reef builders- stromatoporoids, rugose, & tabulate corals (collapse of the reef system). Almost all families of brachiopods, trilobites, ammonites, conodonts, acritarchs, and all placoderms. (The tetrapods barely survived)
Ranking: Third. This extinction was more drastic than that of the Cretaceous.

3. Permian-Triassic extinction event.
Recorded time event: 252 mya (Marked the boundary between the Paleozoic and Mesozoic Eras)
Theorized causes that triggered this event have been documented into the following:
a) The movement of the plate tectonics that united all continents to form Pangea. Formation of the super-continent likely could had altered oceanic circulation and changes in the atmospheres' weather patterns.
b) Massive impacts of large meteors on Earth's surface released heavy quantities of carbon-dioxide into the atmosphere depleting the ozone layer and increasing global warming.
c) A gamma ray burst resulting from a supernova explosion, at thousands of light-years away from Earth, destroyed the ozone layer, and the planet remained exposed to solar UV radiation for thousands of years.
d) Prolonged volcanic activity. The Siberian flood basalt eruption was the biggest volcanic explosion on Earth, lasting millions of years.
e) Over-extended volcanism caused cool water from the poles to warm. The warm water would had not dissolved enough atmospheric oxygen to circulate throughout the ocean current.
Scientists are still not convinced that a single cause would likely had triggered such widespread, cataclysm over the entire planet.
Aftermath: About 95% of all marine species became extinct. Around 70% of all land species were wiped out, also including plants, insects, along with vertebrates.
Extincted species: Systematic, global extermination of almost all marine & terrestrial fauna and flora. (Fungus lifeforms barely survived and became the dominant species for a relative, brief period of time)
Ranking: The worst extinction crisis event the Earth has ever experienced throughout its geological lifetime history.

4. Triassic-Jurassic extinction event.
Recorded time event: 200 mya
It has been speculated that a less combination of few of the factors, which helped bring forth the mass extinction of the Permian period, were responsible for triggering this event. However, they ocurred at a comparatively mini-scale than that of the Permian.
Aftermath: Accounted a 20% of total destruction of marine families. All dinosaurs' ancestors disappeared too.
Extincted species: Crurotarsi, remaining Therapsids, and many large amphibians.
(Dinosaur complete domination of the planet)
Ranking: Fifth. The mass extinction with the least consequences into the world's environment and biodiversity.

5. Cretaceous-Tertiary(Paleogene) extinction event.
Recorded time event: 065 mya (Marked the boundary between the Mesozoic and Cenozoic Eras)
A popular theory for the cause that triggered this event is the "Giant Impact Event".
A speculated 10-Km-wide asteroid crashed on the Earth. The resulting blast would have been millions of times more devastating than that of the most powerful nuclear weapon ever detonated. This in turn would cause gigantic firestorms of ravaging power that would have picked-up dust and vapor and released them into the atmosphere. The dust would clogged together to form a cloud, covering the planet and preventing sunlight for thousands of years thus provoking an extended winter.
Aftermath: Over 50% of the world's total fauna was decimated.
Extincted species: (Most notably) Dinosaurs- theropods, ornithiscians, great sea reptiles, pterosaurs -, bird ancestors- enantiornithes & hesperornithiformes -, many mammal groups, ammonites, some freshwater molluscs families, and many species of phytoplankton.
(Although large birds' ancestors became extincted in this event, some bird families barely survived)
Ranking: Fourth. The most well known and documented of all the extinction events.

Kensuke 2006-03-01 07:43

The latest extinction event (one that killed the dinosaurs) is no doubt the most famous, and it interest me too because probable cause is an asteroid and astronomy is my hobby.
The rate that plant and animal life is disappearing today can by considered as a new mass extinction, and the cause is, of course, we humans. I have read that the average lifetime of a species, from its "birth" to when it becames extinct is about four million years, and human race as a species has existed about that time.

I wonder if there was a message in KonoMini that this is also a threat to human race. :heh:

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