Interdisciplinary research can be challenging because you are hoping to study a topic from different viewpoints - perhaps from a pure sciences perspective, and from a humanities perspective.
Journeying through different disciplines and subject areas makes it useful to be aware of how research is done in different fields.
Are you clear on the difference between the humanities and the sciences? More confusingly, do you understand where the social sciences fit into this puzzle? Here are some guidelines:
Primarily history and the arts, although things like philosophy and religion are included here as well. Check this page from Stanford for a brief overview.
Biology, chemistry, physics, geology etc. When you can stick something under a microscope or zap it in a particle accelerator, you're in the sciences. From the Science Made Simple website, this is an overview of the sciences.
This is the great "grey zone" between the humanities and the sciences. Some "social science" fields are like the humanities, and some are more like the sciences. If you want to use a social science approach to your essay topic, talk to your prof first and ask him or her if it is appropriate. Examples of social sciences include: anthropology, sociology, political science, economics, human geography, cultural studies.
What is quantitative vs. qualitative research?
This page provides a good overview, but here are some quick guidelines:
People in white lab coats measuring and testing physical things and being able to accumulate hard data. When you do quantitative research you can say with certainty that (for example) the concentration of propylene glycol in a section of the Gulf of Mexico in July 2010 was 400 parts per million.
Instead of hard data, you are accumulating information on how people think, and trends in the way large groups of people feel on different topics. If you interview a group of 20 nurses and ask them questions about causes of stress on the job, you are doing qualitative research. You will be presenting your research with language such as "many nurses cite shift work as a cause of stress, because of the burden it places upon family life". Qualitative research examines areas which cannot really be examined with hard numbers. Another example of qualitative research might be emailing 100 people an image of a famous painting, and asking the 100 participants to explain how the painting makes them feel.