Timeline for the History of Life
The age of the Earth is 4.54 billion years. This age is based on evidence from radiometric age
dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar
samples. Following the scientific revolution and the development of radiometric measurements,
uranium-rich minerals showed that some were in excess of a billion years old. It’s hard to wrap your
mind around the concept of 4.5 billion years. For many of us, the Pyramids—built 4,500 years ago, a
millionth of that time span—symbolize the distant past. The geological time scale helps us grapple
with the vast swaths of time that life has existed on Earth, dividing it into eras, periods, and epochs.
Walk the timeline! The number are how many steps away from today the event occurred.
Each step = 50 million years.
Major Events (know the bold)
1. Beginning of the Earth: 4.5 billion year old Earth – 90
2. 3.8 billion yrs simple cells appear (anaerobic bacteria) – 76
3. 2.8 billion years, photosynthetic cyanobacteria release oxygen
into the atmosphere - 56
4. 2 billion years aerobic bacteria appear- 40
5. 1.5 billion years, first eukaryotes appear (protists) - 30
6. 700 million years multicellular organisms - 14
7. 570 million years of arthropods- (ancestors of insects,
arachnids and crustacea) 11.4
8. 500 million years all animal phyla (types) exist - 10
9. 500 million years of fish - 10
10.
430 million years of land plants 8.6
11. 400 million years of insects and seeds 8
12. 360 million years of amphibians 7.2
13. 300 million years of reptiles 6
14. 200 million years of mammals 4
15. 150 million years of birds 3
16. 130 million years of flowers 2.6
17.
65 million years since the non-avian dinosaurs died out 1.3
18. 2.5 million years since the appearance of the genus Homo 0.6
inch
19. 200,000 years since humans started looking like they do today
0.05 inch (1.2 mm)
20. 25,000 years since Neanderthals died out. 0.006 inches / 0.15
mm