What mainly distinguishes nekton from benthos? a) one lives in a freshwater ecosystem and the other lives in salty water. b) one swims freely and the other often lives attached to a hard surface. c) one is a predator and the other is a primary producer. d) all of the above

Answer is B) One swims freely and the other often lives attached to a hard surface.

Nektons are marine aquatic actively-swimming organisms. Nektons propel in the water column freely either by swimming or other by means. Examples include vertebrates such as fish, whales, turtles, sharks and invertebrates include squads.

Benthos are the animals which are found at the bottom of the seafloor. These animals can be free moving forms near the ocean bed or attached to the seafloor. Unlike the nektons, benthos cannot swim in water. Benthos mainly includes echinoderms, crustaceans, molluscs, poriferans and annelids.

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

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