Historical geology

Historical Geology


Vastness of time




The act of comprehending is defined as a person's ability to understand a concept completely. When a human attempts to understand geological time they run into the problem of understanding numbers. Let's assume that understanding is related to experience. The number “10” is easy to understand since not only is it easy to count even as a child, but a standard human hand has ten digits. Let's continue that assumption and view “100”. The number takes long to count, but it can be done in minutes and can be viewed easily.



10 randomly selected people were timed for their ability to count in a clear and understandable fashion. The average time to count ten seconds was 3.75 seconds[citation needed]. The average showed that every second a person is able to count 2 single digit numbers. We will assume I can keep this pace even as the number of symbols of the pronunciation of the number increases such as saying “9” compared to “9,999” and use a precision of whole numbers for seconds.

NumberTime required to count
21 second
1,000,0005 days 18 hours 53 min 20 sec
1,000,000,00015 years 312 days 0 hours 53 min 20 sec



The time required to count to one billion would take a person almost 16 years to count if they count at a continual pace. Earth is currently thought to be 4.5 billion years old. Just counting to that number would take about 70 years. That's nearly a human lifetime. This number is simply incomprehensible due to its vastness.

Geological Time


Geology Time and a Clock


Each geological time unit can represent a unit of daily time. An Eon can stand for hours, era for minutes, periods for second, and epoch for milliseconds.

As the animation shows. Time starts at the beginning of the Earth and continues to the present 4.6 billion years later. Eons change and has Eons move on Era's change. Era are a division of Eon's. This is the same for Periods and Epochs. The units of time increase in precision and decrease in scale. Comparing the Eon clock rotation to the Epoch rotation and you can see how small Epoch and even Eras are in the scale of geological time.



The geological time scale is measured in Million Years Ago (Mya).

Geological Time Scale


Eoarchean Era(? - 3600 Mya)

Paleoarchean Era (3600 Mya - 3200 Mya)

Mesoarchean Era (3200 Mya - 2800 Mya)

Neoarchean Era (2800 Mya - 2500 Mya)

Paleo-Proterozoic Era (2500 Mya - 1600 Mya)

Meso-Proterozoic Era (1600 Mya - 1000 Mya)

Neo-Proterozoic Era (1000 Mya - 542 Mya)

Cambrian Period (542 Mya - 488 Mya)

Ordovician Period (488 Mya - 443 Mya)

Silurian Period (443 Mya - 416 Mya)

Devonian Period (416 Mya - 359 Mya)

Mississippian Period (359 Mya - 318 Mya)

Pennsylvanian Period (318 Mya - 299 Mya)

Permian Period (299 Mya- 251 Mya)

Triassic Period (251 Mya - 200 Mya)

Jurassic Period (200 Mya - 145 Mya)

Cretaceous Period (145 Mya - 65 Mya)

Palocene Epoch (65 Mya - 55 Mya)

Eocene Epoch (55 Mya - 34 Mya)

Oligocene Epoch (34 Mya - 23 Mya)

Miocene Epoch (23 Mya - 5 Mya)

Pilocene Epoch (5 Mya - 1.8 Mya)

Pleistocene Epoch (1.8 Mya - .01 Mya)

Holocene Epoch (.01 Mya - Present)



USGS Geological Time by William L. Newman