1.3: Measurements in Geology
Measurements in Geology
Observations and measurements are used in all of the sciences. An observation Links to an external site. is information obtained directly from one of the five human senses. A measurement Links to an external site. is a means of expressing an observation with great accuracy. Measurements are expressed by both a numerical value and a unit. It is critically important to always ensure your number has a unit! In the US, we use two systems to measure: the English or Imperial System Links to an external site. and the Metric or International System Links to an external site. (SI). Typically, scientists will utilize the metric (SI) system for consistency.
Common geologic measurements
- Length: the distance between two points
- Mass: the amount of matter in an object
- Time: the duration of the event being observed
- Temperature: a measure of kinetic energy, commonly known as heat.
If you are unfamiliar with measurement abbreviations, the following tables may be a helpful reference.
| Imperial System Abbreviation | Imperial System Measurement | Metric System Abbreviation | Metric System Measurement |
| -- | -- | mm | millimeter |
| in | inch | cm | centimeter |
| ft | feet | m | meter |
| mi | mile | km | kilometer |
| °F | Fahrenheit | °C | Celsius |
Measurement conversions are an important part of the sciences. If you struggle with math, remember, you are better than math! Math is a skill to learn, in the same way you learned to read and write. Like learning a language, it takes consistent practice to become fluent. The internet contains a wealth of information -- good, bad, and ugly. You will likely find many conversion tools with a simple Google search; however, the process behind conversions is helpful to learn, particularly if you plan to enter a STEM-based field. Help on conversions is available Links to an external site.here Links to an external site..
Occasionally you many encounter measurements reported in scientific notation Links to an external site.. Scientific notation will contain exponents and is useful for measurements that are very small or extremely large (Table 1.2).
| Decimal notation | Scientific notation |
| 2.0 | 2 x 100 |
| 300 | 3 x 102 |
| 4321.768 | 4.321768 x 103 |
| -53,000 | -5.3 x 104 |
| 6,720,000,000 | 6.72 x 109 |
| 0.2 | 2 x 10-1 |
| 987 | 9.87 x 102 |
| 0.00000000751 | 7.51 x 10-9 |
Scientific Error
When recording measurements, scientists will sometimes indicate scientific error. Errors are differences between observed values and what is true in nature. For measurements, scientists commonly consider both accuracy (how close a measurement is to the true or accepted value) and precision (how close measurements of the same item are to each other). Precision is always independent of accuracy (Figure 1.11). The best quality scientific observations are both accurate and precise.
Figure 1.11: It is possible to be very precise but not very accurate, and it is also possible to be accurate without being precise. In this example, the closer the darts land to the bulls-eye, the more accurate they are. (CC-BY 4.0; Emily Haddad, own work).
What Is Rounding?
Rounding makes a number simpler but ensures it remains close to the original value. The rounded result is less accurate, but easier to use. This is why you should never round until you are ready to calculate the final answer. Your instructor will likely let you know to what place they would like you to round. So, how do you round numbers? First, identify which place value your instructor prefers you round to (whole number, tenth, hundredth, etc.); ask for clarification if you are unsure. Second, look to the next smallest place value, the digit to the right of the place value you're rounding to. If the digit in the next smallest place value is less than five, you leave the digit as-is. Any digits after that number (including the next smallest place value you just looked at) become zeros, or drop-off if they're located after the decimal point. This is rounding down. If the next smallest place value is greater than or equal to five (5, 6, 7, 8, or 9), you increase the value of the digit you're rounding to by one. Just like before, any remaining digits before the decimal point become zeros, and any that are after the decimal point are dropped. This is called rounding up.
For example, if we were to round 1.75 cm to the nearest tenth, the new value would become 1.8 cm. If we were asked to round 1.75 cm to the nearest whole number, the new value would become 2 cm.