Is it an Observation or an Interpretation?

In our daily life, we are constantly making observations of our surroundings. We notice whether cars are coming when we walk across the street, and we observe the reading on our watch to see if we have an appointment coming up. Is our observation "True?" Maybe, but in science we need to be aware that observations are subject to assumptions. We assume that our clock's time is correct (or not) and assume that cars are driving along the street and not dropping out of the sky. We do this to narrow down the amount of information we need to process before we act. Our "observation" is a piece of data or sensory input that we decide to trust, or that is appropriate to the situation.

For example, suppose you are a geologist and you have collected a rock from the field site you are studying. You want to determine the date at which the rock crystallized so that you can make a theory about how your site evolved. So, you send the rock to the lab to get it analyzed. The analyst grinds it up and puts it into a mass spectrometer that measures the radioactive isotope ratios. The analyst's observation will be the isotope ratio. She then calculates the age and emails it to the geologist. To the analyst, the observation is the isotope ratio and the interpretation is the age, but to the geologist, the observation is the age and the interpretation is the tectonic model of how the sites evolution.

So, the determination of whether a statement is an observation or an interpretation is determined by the purpose or type of investigation. For another example, suppose you are using the earthquake location data to study a plate tectonic boundary. You will consider that the location of the earthquakes are the observations and your assertions about what type of plate tectonic boundary created them will be the interpretations.

The question a scientist must address, though, is whether the observations are sufficient to support the interpretation. For the plate tectonics example, the accuracy of the earthquake locations must be considered. Their accuracy will determine how accurately the zone of earthquake activity can be located. One important artifact occurs in earthquake location data in regions distant from land stations. It appears that some quakes lie on a horizontal line at 35km depth. Seismologists know that this is an artifact of the earthquake location computation caused by the lack of close seismograph stations. The location program puts quakes with insufficient information to determine the depth at 35km. So, this creates the false illusion of a horizontal fault.

For the purpose of your investigations using the Solid Earth Data browser, you can consider the data plots that it creates to be your observations. If you are accessing this from the Earth Exploration Toolbook, the maps and earthquake plots should be considered to be your observations.