At this point in time, the field of Astrobiology is concentrating primarily on the discovery of life, either extinct or existent, upon the face of Mars. The field of Astrobiology is concentrating on three different questions...
1) To what extent did prebiotic chemical evolution proceed on mars?
2) If chemical evolution occurred, did it lead to teh synthesis of replicating molecules that subsequently became extinct?
3) If replicating systems arose on Mars, do they persist today?
The reason that astrobiologists believe that there may be or may have once been life on the Red Planet is because both Mars and Earth had similar histories. It is highly likely that since life on Earth developed so very quickly, it did the same on Mars.
As you can see, the fields of Astrobiology and that of Areopaleontology/Areopaleogenomics are following each other very closely at this point in time. It may be possible in the coming years for the the two fields to diverge as space travel becomes possible. Until then, these two fields will probably work together to each further their own means.