I am more of a chemist than a biologist and more of a biologist than a geologist.
Using molecular compounds that are associated with known processes (those in the business refer to these compounds as biomarkers) I learn how Earth has evolved through time - from the earliest iron and sulfur rich oceans, to the first signs of life, on to the rise of oxygen, to the demise of the dinosaurs, and all the way up and through modern day processes.
This approach can be described as organic geochemistry, geobiology, or biogeochemistry. No matter what you call it, the best part is being able to use my knowledge of chemistry (my first scientific love) to inform and answer compelling questions in geology and environmental science.
It's like being a detective and a historian. I get to tell the tales that Earth has chronicled by deciphering the language they are written in - which can be intimidating and ambitious, but most of all it's exciting!
Samples at various stages in their work-up for instrumental analysis
...to collect facts for their own sake, as many now gather facts, without a program, without a question to answer or a purpose is not interesting. However, there is a task which someday those chemical reactions which took place at various points on earth; these reactions take place according to laws which are known to us, but which, we are allowed to think, are closely tied to general changes which the earth has undergone by the earth with the general laws of celestial mechanics. I believe there is hidden here still more to discover...