Passive vs active voice
The use of either passive or active voice in scientific writing often depends on the style and goal of the text. Passive voice generally focuses more on the action (i.e. the verb) of an object rather than the subject in a sentence. Active voice is defined by a subject taking action upon an object. For example, one might choose to say, passively: “The orientation of slickensides was measured in three locations”, in which the emphasis lies on the object (the slickensides) and the action (was measured). In active voice, the sentence would be: “We measured the orientation of slickensides in three locations”, i.e. highlighting the subject (we) simultaneously to the action and object.
Traditionally, scientific texts relied on the use of passive voice; however, there has been a more recent shift towards active voice use in scientific publications. Sometimes, passive voice is conceived as more objective, but sentences using passive voice are also lengthier, impersonal, and may be perceived as boring. In texts where you present your own results next to cited results from other scientists, passive voice may confuse your audience as it could be unclear whose results you are actually discussing. In contrast, active voice is more concise and unambiguous; it appropriately describes science, which is actively performed by scientists. Because the purpose of scientific texts is to transfer knowledge and ideas to an audience, it is valuable to write it down in such a way that it cannot be interpreted incorrectly, or out of context. The unambiguity of active voice is a useful tool to do so. Despite this, the focus on subject (we, I) in active voice both is still not always preferred by readers and reviewers. In some (research) cultures and countries, a fully active text is therefore not always applied. An example of the focus on subject:
“We measured the metal concentrations in the water samples by ICP-OES”; i.e. active voice: emphasis lies on subject (we) as well as action and object.
“The metal concentrations in the water samples were measured by ICP-OES”; i.e. passive voice: emphasis lies on action (measure) applied to object (metal concentrations in samples).
The debate over the use of either active or passive voice in scientific writing is also ongoing amongst the instructors of the Earth Science programmes at Utrecht University. Therefore, make sure to check the requirements of your assignment, thesis, or journal paper and ask supervisors/editorial boards for their preferences if you are unsure what voice to use.
Most importantly, remain consistent in your voice use, and remember to clarify which results were obtained by what research group (i.e. separate your own results from those of others and correctly apply references). Also, keep in mind that in Earth Science we often describe actions (e.g. deposition of sediments, deformation etc.) to which the subject is unclear or unimportant. In such cases, passive voice is preferred, and such contexts allow for a deviation from a generally active narrative in the rest of your text. For example:
“During the early Malm (Oxfordien) thick layers of dark marl were deposited. We analysed samples from this deposit using XRF.”;
In the first sentence the subject is unclear (and unimportant) and the action (deposition) and object (marl) are emphasized. In the second sentence active voice is used as it refers to the action taken by the authors.