The external intercostals elevate the rib cage during

Inhalation

Explanation:

The intercostal muscles consists of three sets of superimposed muscles located between adjacent ribs. These sets of muscles is made up of the external intercostal, internal intercostal, and innermost intercostal muscles.

The external intercostal muscles are involved in inhalation,and the elevate the rib during this process.

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.

hope this .. .