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2019-12-17 12:57:16.0 [tstevens] Insert Concept
add narrower relation (ORDOVICIAN [02f8be65-6bdd-4f4d-9e69-adac5aec33f6,505095] -
UPPER [479caf3a-2744-4cef-b992-745c1ffd3e96,532251]);
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2019-12-17 12:57:26.0 [tstevens] Insert Concept
add narrower relation (ORDOVICIAN [02f8be65-6bdd-4f4d-9e69-adac5aec33f6,505095] -
MIDDLE [e941d527-8935-4b63-b76f-5febd609b9b5,532255]);
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2019-12-17 12:57:33.0 [tstevens] Insert Concept
add narrower relation (ORDOVICIAN [02f8be65-6bdd-4f4d-9e69-adac5aec33f6,505095] -
LOWER [00c6f0f3-5734-4500-a69e-f6780e365985,532259]);
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2019-12-17 13:22:47.0 [tstevens]
insert Definition (id: null
text: The Ordovician Period lasted almost 45 million years, beginning 488.3 million
years ago and ending 443.7 million years ago. During this period, the area north of
the tropics was almost entirely ocean, and most of the world's land was collected
into the southern supercontinent Gondwana. Throughout the Ordovician, Gondwana shifted
towards the South Pole and much of it was submerged underwater. The Ordovician is
best known for its diverse marine invertebrates, including graptolites, trilobites,
brachiopods, and the conodonts (early vertebrates). A typical marine community consisted
of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids,
and gastropods. More recently, tetrahedral spores that are similar to those of primitive
land plants have been found, suggesting that plants invaded the land at this time.
From the Lower to Middle Ordovician, the Earth experienced a milder climate — the
weather was warm and the atmosphere contained a lot of moisture. However, when Gondwana
finally settled on the South Pole during the Upper Ordovician, massive glaciers formed,
causing shallow seas to drain and sea levels to drop. This likely caused the mass
extinctions that characterize the end of the Ordovician in which 60% of all marine
invertebrate genera and 25% of all families went extinct.
language code: en);
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| definition |
The Ordovician Period lasted almost 45 million years, beginning 488.3 million years
ago and ending 443.7 million years ago. During this period, the area north of the
tropics was almost entirely ocean, and most of the world's land was collected into
the southern supercontinent Gondwana. Throughout the Ordovician, Gondwana shifted
towards the South Pole and much of it was submerged underwater. The Ordovician is
best known for its diverse marine invertebrates, including graptolites, trilobites,
brachiopods, and the conodonts (early vertebrates). A typical marine community consisted
of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids,
and gastropods. More recently, tetrahedral spores that are similar to those of primitive
land plants have been found, suggesting that plants invaded the land at this time.
From the Lower to Middle Ordovician, the Earth experienced a milder climate — the
weather was warm and the atmosphere contained a lot of moisture. However, when Gondwana
finally settled on the South Pole during the Upper Ordovician, massive glaciers formed,
causing shallow seas to drain and sea levels to drop. This likely caused the mass
extinctions that characterize the end of the Ordovician in which 60% of all marine
invertebrate genera and 25% of all families went extinct.
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