The protist known as an euglena is sometimes considered an animal-like protist and other times a plant-like-protist. why would scientists classify it as an animal-like protist?

Euglena is unicellular micro-organism which belongs to protista kingdom, mostly found in fresh water. Because of their unique characteristics sometimes they are considered as plant-like and sometimes animal-like.

Most of the euglena contains photosynthesizing chloroplast within the body of the cell, like plants.

Euglena cell contain flagella and tail which allow moving, it is the characteristic of animal like. When euglena goes into the darkness environment it's cell will engulf the food by phagocytosis. They have eyespot which is sensitive to light and compair to modern eye and these are the characteristic of animals.

This is why they are considered as both plant and animal-like.

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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