How can the age of fossils be determined?

In humans,the nictitating membrane is a/an....

According to Darwinism,the fossils of organisms found in South America most closely resemble the fossils of:

In the evolutionary history of the human heart,it is observed that it passed through a two-chambered heart like that of fish,to a three-chambered heart like that of amphibians,and finally became a four-chambered heart. Which concept is closest to this statement?

Select the appropriate option for the work done by $Ernst$ $Haeckel$.

State the modifications of forelimb in animals as an example of homology.