Archaeology is the study of physical, non-biological evidence left behind by past human cultures. Archaeologists are especially important to the field of anthropology because many human cultures of the past predate writing and therefore left no records behind. Archaeologists are invaluable to the study of virtually all past cultures, and can be subdivided based on the time periods and regions that they work with (for example, classical archaeologists focus on ancient Mediterranean societies such as Rome and Greece).
Linguistics is the study of how human beings in past and present cultures communicate. Both verbal and non-verbal communication (such as facial expressions) are included in linguistics, as well as writing. Linguists often focus their study on smaller, present-day cultures that have not been exposed to modern dominant languages in order to determine which attributes of their niche language overlap with languages of others.
Biological anthropology focuses on how homo sapiens (the scientific classification of human beings) have evolved throughout their 2 million years of history, as well as what differentiates homo sapiens from their precursors. Given the course of evolution and human links with past and present-day primates, biological anthropologists often study non-human biology as well. Biological anthropologists are constantly having to adapt their theories to adjust for new-found discoveries from our primitive primate past.
Cultural anthropologists seek to identify trends in how human societies establish and maintain themselves. This involves an examination of a culture's mores, which includes everything from what they eat, to clothing, to how they select their leaders. Much like linguistic anthropologists, cultural anthropologists looks at both past cultures as well as smaller, sequestered present-day cultures in order to try to identify trends that are common in the whole of humanity.