geo

A Tour of Geologic Time

Introduction
Geologic time can be defined as the time over which the Earth has formed into the present-day Earth we know today. It is difficult for most students to grasp just how much time has passed since the Earth formed, and the huge amount of life that has now disappeared. Scientists estimate that 99% of all the life that has ever lived on Earth is now gone.
We understand that the Earth is about 4.7 billion years old. We’re now finding that the Earth cooled enough to support life by about 4.2-3.9 billion years ago. There are some controversial reports of biological structures and chemical structures that indicate life was beginning at or about 3.8 billion years ago.
One thing is certain—the rocks that formed in that early Earth scenario show a global lack of oxygen in the atmosphere and oceans. The only life forms are unicellular bacterial types, but amongst this group, some evolve the ability to turn light energy into chemical energy (early photosynthesis).
It took these early photosynthesizers a long time, but eventually, over the next billion years, the atmosphere and oceans are oxygenized to the point where other bacteria can use oxygen to reverse photosynthesis and create energy molecules from simple sugars (carbohydrates).
This is the point where we can explore the long history of Earth’s past and, perhaps, its future as well.
Note:

Part 1: Understanding the geologic timeline
Visit the link below and explore the geologic timeline; this will help you tremendously in completing the activity in part 2: https://rmpbs.pbslearningmedia.org/resource/tdc02.sci.ess.earthsys.deeptime/deep-time/
Part 2: Making your own geologic timeline
Procedure:
1. Obtain a piece of string or tape (like that used in crime scenes) to make your timeline. You’ll make 2 timelines—1 of geologic time in general, and 1 chosen from the 3 major periods containing life: Paleozoic, Mesozoic, or Cenozoic.
A. Geologic Time Overall
You’ll need a 5 meter length of string/tape (tape will work better). Anchor each end in the ground or floor with a pin/tack or adhesive tape. Remember that Ma = mega annum (million years) and Mya is millions of years ago, and bya is billions of years ago. For this exercise, each meter represents 1 billion years. Measure, from the far left edge, the Hadean Eon by subtracting 4.6bya from 5.0bya, giving you 0.4m from the left edge. Continue to plot the Eons and Eras on your 5m tape. Don’t forget to take a photo of the finished product.

B.
Repeat the process, but this time with only 1 Era chosen from Paleozoic, Mesozoic, or Cenozoic eras, and complete with the Periods for your chosen Era within that timeline.

Analysis Questions:
1. In which Eon did life appear?
2. In which Eon did the atmosphere become oxygenated?
3. In which Eon did multicellular life appear?
4. In which Eon did we see life on land?
5. In which Eon do we see the dinosaurs go extinct?
6. Which Era did you choose?
7. List the Periods of your era in order from newest to oldest.
8. In each Period, what was the dominant life form?
9. In each Period, what was the climate like overall?
10. In each Period, did any life go extinct? If so, list two or three types that went extinct.

Geologic Time Scale:
Eon Era Period Dates (Ma)
Phanerozoic Cenozoic Quaternary 2.58-0
Neogene 23.03-2.58
Paleogene 66-23.03
Mesozoic Cretaceous 145-66
Jurassic 201-145
Triassic 252-201
Paleozoic Permian 299-252
Carboniferous 359-299
Devonian 419-359
Silurian 444-419
Ordovician 485-444
Cambrian 541-485
Proterozoic Neoproterozoic Ediacaran 635-541
Cryogenian 720-635
Tonian 1000-720
Mesoproterozoic Stenian 1200-1000
Ectasian 1400-1200
Calymmian 1600-1400
Paleoproterozoic Statherian 1800-1600
Orosirian 2050-1800
Rhyacian 2300-2050
Siderian 2500-2300
Archean Neoarchean   2800-2500
Mesoarchean   3200-2800
Paleoarchean   3600-3200
Eoarchean   4000-3600
Hadean     4600-4000
Eon Era Period Dates (Ma)

Source: https://www.thoughtco.com/geologic-time-scale-eons-eras-periods-1440796