If the producers in this aquatic food chain produce 50,000kcal of energy; how much energy would the Perch have?

The perch have 500 kcal of energy.

Explanation: Perch is a type of fish which feed on zooplankton, so it belongs to secondary consumer in the trophic levels. In aquatic ecosystem, plants are the producer which contains 50,000 kcal of energy. When these plants are eaten by primary consumer i. e. zooplankton, so only 10 % of energy is transferred about 5000 kcal. When zooplankton are eaten by perch fish, so 10 % energy is transferred again i. e. 500 kcal.

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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