Question

How do geologists determine how rocks were formed?

Answer 1

Geologists try and observe as many features in the rock and then develop an interpretation based on observations.

Explanation:

Field geologists will typically visit a number of different locations in a day and record data such as:

• geographical locations (Lat./long)
• geological formation if known
• strike and dip of the strata (if they are trending or dipping)
• rocks that lie above and below in a succession - type, color, etc.
• type of rock (sedimentary sandstone, basalt, gneiss, etc)
• description and thickness of the rocks (color, minerals, fossils present, bedding, etc).
• a sample is often taken to study back in the lab and this requires banging on the rock to produce some "fresh surfaces" wherein the minerals can be seen. Hand lenses are also used to see fine mineral grains.
• sedimentary structures if present, such as ripple marks, mud cracks, trace fossils, etc.

Once the geologist has all the field data in hand, they can start to interpret the rocks and come up with ideas related to how the rocks formed (e.g. a sandstone might have been deposited in an ancient beach environment). It is really important though to keep observations separate from interpretations!