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What important function did rudists perform during the cretaceous?
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What are five prehistoric small marine creatures?
Trilobites ranged in size from about half an inch to around two feet in length. Haikouicthys, one of the earliest known fish, was about an inch long. Ammonites ranged in size from around 9 inches to some species as large as 6.5 feet. Anamolocaris was a huge apex predator for its time, but by modern standards wasn't very large, only measuring three to six feet long. Rudists, a type of bivalve that was so common during the Cretaceous, piles of them formed reefs. They ranged from a few centimeters to over a meter in length, depending on the type.
What rocks have carbonate in them?
Sedimentary rocks are usually divided into: siliciclastic rocks and carbonate rocks. Siliciclastics are usually composed of the weathering products of older rocks carried and delivered to a basin of deposition by rivers. Carbonate rock, however, are generally composed of carbonate minerals (e.g. Calcite, Dolomite, Anhydrite..) these minerals form either biologically (as skeletons of sea organisms such as foraminifera, rudists and corals) or chemically by sea water. The most famous carbonate rock is probably Limestone, other rocks include: Dolostone (aka Dolomite) and evaporites; interesting to note that Marble is metamorphosed limestone.
Where is calcite found on earth?
The largest documented single crystals of calcite originated from Iceland, measured 7×7×2 m and 6×6×3 m and weighed about 250 tons. Calcite is the primary mineral in metamorphic marble. It also occurs as a vein mineral in deposits from hot springs, and it occurs in caverns as stalactitesand stalagmites.Calcite is a common constituent of sedimentary rocks, limestone in particular, much of which is formed from the shells of dead marine organisms. Approximately 10% of sedimentary rock is limestone. Lublinite is a fibrous, efflorescent form of calcite. Calcite may also be found in volcanic or mantle-derived rocks such as carbonatites, kimberlites, or rarely in peridotites. Calcite is often the primary constituent of the shells of marine organisms, e.g., plankton (such as coccoliths and planktic foraminifera), the hard parts of redalgae, some sponges, brachiopods, echinoderms, most bryozoa, and parts of the shells of some bivalves (such as oysters and rudists). Calcite is found in spectacular form in the Snowy River Cave of New Mexico as mentioned above, where microorganisms are credited with natural formations. Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. Calcite seas existed in Earth history when the primary inorganic precipitate of calcium carbonate in marine waters was low-magnesium calcite (lmc), as opposed to the aragonite and high-magnesium calcite (hmc) precipitated today. Calcite seas alternated with aragonite seas over the Phanerozoic, being most prominent in the Ordovician and Jurassic. Lineages evolved to use whichever morph of calcium carbonate was favourable in the ocean at the time they became mineralised, and retained this mineralogy for the remainder of their evolutionary history. Petrographic evidence for these calcite sea conditions consists of calcitic ooids, lmc cements, hardgrounds, and rapid early seafloor aragonite dissolution. The evolution of marine organisms with calcium carbonate shells may have been affected by the calcite and aragonite sea cycle.
