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Permian Period (290-248 mya)
A great merger of northern and southern landmasses creates the
supercontinent Pangaea. Stretching from pole to pole and surrounded almost entirely
by a single world ocean called Panthalassa, Pangaea's dry interior fluctuates in
temperature far more than its coastal zones, which are moderated by nearby water.
On land, reptiles continue to evolve. Mammal-like reptiles, precursors
to the true mammals, appear and quickly radiate. Seed-producing gymnosperms, which include
the conifers and the cycads, begin to replace lycophytes as the dominant
plant group.
In the oceans, brachiopods, ammonoids,
crinoids, bony fishes, and sharks still thrive, but rugose corals, tabulate corals,
and trilobite populations are on the wane. A catastrophic
extinction near the close of the period -- several times worse than any other --
nearly ends the entirety of life on land and in the seas.
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280 mya: Cycads
With a stout trunk and leafy crown, cycads provide vegetation and
canopy cover to animals. Cycad fossils -- leaves, stems, cones, and seeds -- are found
on every continent, suggesting these gymnosperms thrived in diverse climates over time.
Modern species exist only in tropical regions, however.
280 mya: Pangaea supercontinent forms
By the early Permian, Earth's major land masses -- Gondwana,
Laurussia, and Siberia -- fuse with smaller continents to form the supercontinent
Pangaea. Pangaea, which means "all the Earth," stretches nearly from pole to pole.
Where plates converge, crust folds and mountains form. Pangaea is surrounded almost
entirely by a massive ocean, Panthalassa. A secondary body of water, the Tethys Ocean,
cuts into the east of Pangaea near the equator.
280 mya: Drying trend begins
The interior of Pangaea begins to dry.
275 mya: Mammal-like reptiles
Mammal-like reptiles are cold-blooded, but they spawn true,
warm-blooded mammalian successors. They are the dominant land vertebrates during
the Permian, but despite their early success, only two families will survive into
the next period.
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End Permian extinction
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Date:
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250 mya
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Intensity:
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1
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Affected:
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Approximately 90 percent of all
species, including nearly 57 percent of marine families and nearly 70 percent of
land vertebrate families go extinct
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Hypotheses:
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Volcanic activity, glaciation,
sea-level changes, changes in ocean chemistry, global warming, meteor impact
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Summary:
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In the most devastating of
all extinctions, an estimated 90 percent of all species are eliminated over
two pulses, spaced about 8 million years apart.
All remaining trilobites, all graptolites,
and nearly all echinoderms are killed off. The brachiopods,
dominant through most of the Paleozoic era, will be only a minor marine invertebrate
group in the Mesozoic and Cenozoic eras. Marine predators such as sharks and
coelacanths are hit hard, and coral reefs will require at
least 10 million years to recover. Among the land animals, two-thirds of amphibian
families, all large herbivores, and most reptiles die out. Terrestrial plants also
suffer greatly.
The extinction might be the result of a combination of
factors, including massive glaciation, changes in sea level, and either an
oversupply of carbon dioxide or an undersupply of oxygen in the oceans. Some
of these conditions might have been triggered by volcanic eruptions in Siberia,
or perhaps even by a meteor impact.
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Read more
The mother of all extinctions (250 mya)
Marine communities are at their most diverse, and flora and
fauna radiate on land throughout the Permian period. The end Permian
extinction is the closest that life has come to complete annihilation in the past
600 million years, if not the entire history of Earth.
- In the oceans, approximately 57 percent of all marine
families die out, which is about 400 families. On the species level, 90-95
percent may have perished. That means as few as 12,500 out of 250,000 marine
species may have survived.
- On land, more than 70 percent of all vertebrate families
are wiped out, including approximately 75 percent of all reptiles and
approximately 67 percent of the amphibians. Most plant life disappears, as
does nearly 33 percent of insect orders, marking the only time insects have
ever suffered mass extinction.
The extinction generates a complete reorganization of both
marine and terrestrial life. Dominant groups that vanish leave several ecological
roles vacant. Many of the groups that fill these roles in the subsequent period
persist through the Mesozoic and, in some cases, to the present day.
The cause of this extinction is still largely unresolved.
Some hypotheses suggest that slow but progressive changes in climate
or sea level were responsible. Other hypotheses point to quick-hitting, catastrophic
events such as extraordinary volcanic activity. Still others suggest a combination
of factors may have contributed to the mass killing.
In 2001, a new hypothesis was put forward. Scientists found
traces of iridium in rocks dated to the time of the extinction. Iridium is scarce
in Earth's crust but plentiful in asteroids, and the scientists think an asteroid
as large as seven miles across might have slammed into Earth, releasing at least
a million times more energy than the strongest recorded earthquake. But until more
conclusive evidence like a large impact crater is found, this hypothesis will
remain, like others, an intriguing but unproven explanation.
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