Eesti Loodusmuuseum/Näitus/Müstiline ürgmeri/ENG: erinevus redaktsioonide vahel
Eemaldatud sisu Lisatud sisu
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18. rida:
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Placeholder 4-3 wmf blue.svg| Jellyfish. Ancient jellyfish-like cnidarians may have lived in the waters here because fossils of such creatures have been found in Northwest Russia.
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=== THE [[:en:w:Cambrian|CAMBRIAN]] ===
;BALTICA SEPARATES
About 500 million years ago, the majority of land was united in the supercontinent [[:en:w:Gondwana|Gondwana]], which extended from the Northern Hemisphere across the equator to the South Pole. Just the small palaeocontinent Baltica, which comprised the territory of present-day Estonia, and a few other smaller continents were drifting independently from the South Pole towards the equator. As Baltica still remained rather close to the South Pole in the Cambrian period, the shallow sea in its inland remained cool and still rather poor in life.
;THE CAMBRIAN EXPLOSION
The Cambrian period saw a worldwide rapid appearance and spread of marine life, which has come to be known as the [[:en:w:Cambrian explosion|Cambrian explosion]]. Favourable environmental conditions enabled previously soft-bodied creatures to start growing protective mineral shells, or exoskeletons. This afforded those primitive creatures protection from predators and allowed them to colonise nutrient rich coastal areas exposed to strong waves. New taxonomic groups of animals appeared, such as [[:en:w:trilobite|trilobites]], the ancestors of modern arthropods. The shallow sea covering the territory of Estonia also hosted various ringed worms, beard worms, molluscs and moss animals.
''In the Cambrian, the territory of Estonia was shaken by a powerful meteorite explosion, which created the [[:en:w:Neugrund crater|Neugrund crater]], an about
ten-kilometre-diameter impact crater in present-day Northwest Estonian coastal sea.''
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Placeholder 4-3 wmf blue.svg| †''[[:en:w:Micromitra|Micromitra]] undosa''. Brachiopods were solitary invertebrates that attached to the seabed by means of a stalk or burrowed into mud.
Estonian Museum of Natural History - Hazelia Palmata.png| †''[[:en:w:Hazelia|Hazelia]] palmata''. Sponges are the most primitively built immobile multicellular creatures.
Estonian Museum of Natural History - Halkieria.png| †''[[:en:w:Halkieria|Halkieria]]''. A bottom-dwelling creature reminiscent of present-day slugs, with tiny shells resembling the valves of a bivalve shell at both ends of its body.
Estonian Museum of Natural History - Stromatocystites Balticus.png| †''Stromatocystites balticus''. Some echinoderms were starfish-like invertebrates that lived attached to the seabed.
Estonian Museum of Natural History - trilobite - Hydrocephalus.png| †''[[:en:w:Hydrocephalus (trilobite)|Hydrocephalus]]''. Trilobites were the ancient arthropods. The back of their body was covered with a hard outer skeleton; many species had well-developed compound eyes.
Placeholder 4-3 wmf blue.svg| †''[[:en:w:Scenella|Scenella]] discinoides''. Ancient mollusc with calcareous shell who looked like seashells today
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=== THE [[:en:w:Ordovician|ORDOVICIAN]] ===
;THE PERIOD OF SEAS
The Ordovician was characterised by worldwide intense volcanic activity, a meteorite shower, and rapid evolution of life. The Ordovician ended with an ice age, which, either directly or indirectly, led to the second-largest biotic extinction in Earth’s history. By about 460 million years ago, the independent palaeocontinent Baltica, including the territory of present-day Estonia, had shifted from the South Pole to subequatorial tropical waters. The ocean level was high and nearly the entire Baltica continent, including the present Baltic countries and a big part of Scandinavia, was flooded by a shallow tropical sea.
;ICE AGE ON ITS WAY
The ice age was preceded by global climatic cooling, while the Baltica continent enjoyed a mostly tropical climate as it was drifting closer and closer to the equator. The warm shallow sea here supported a thriving marine life dominated by animals with strong protective calcareous shells. The already widespread trilobites, sponges and worms were supplemented by new animal groups — [[:en:w:Coral|corals]], [[:en:w:Graptolithina|graptolites]], [[:en:w:Stromatoporoidea|stromatoporoid]] [[:en:w:Sponge|sponges]], and predatory [[:en:w:Cephalopod|cephalopods]] known as [[:en:w:Nautiloid|nautiloids]].
''In the Ordovician, the present-day area of [[:en:w:Hiiumaa|Hiiumaa]] was shaken by a meteorite impact that created the approximately four-kilometre-diameter [[:en:w:Kärdla crater|Kärdla crater]].''
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