The age of Earth and the fossil record are intimately interconnected. In studying one you are ultimately studying the other and, by extension, the theory of evolution. There are many interesting subtopics in the history of life ,but I tend to look at it in this order of firsts. As is the nature of science and discovery – each of these is subject to change as new discoveries are made. In fact, there is no fully established theory for how life first came to arrive on Earth. Be it panspermia (from meteors) or abiogenesis (from nothing). Carl Sagan has a wonderful YouTube video on abiogenesis. This is a great way to start a unit as it truly captures students’ imagination. Regardless of where you turn is an abundance of great research opportunities for students to dig deeper.
1. First earth forms from solar nebulae
2. Moon forms
3. First evidence of life – prokaryote
4. First evidence of nucleus – eukaryote (endosymbiosis?)
5. First evidence of multicellular life
6. First evidence that oxygen becomes abundant (banded iron formations)
7. First evidence of massive explosion of life forms :Cambrian explosion of life
8. First plants
9. First fish
10. First amphibian
11. First reptile
12. First dinosaur
13. First mammal
14. First flowering plant
15. First lungs
16. First limbs
17. First amniotic egg
18. First feather
19. First live birth
20. First hominid
21. Mass extinctions (5)
22. Are we in the midst of the 6^th mass extinction
My personal favorite time period above all else is the Cambrian. It is during the early Cambrian when evolution shows off its proverbial “guns.” Having had the chance to work at Yale Peabody in the invertebrate lab and see some of the original Burgess Shale specimens was an honor and experience I will never forget.
Of course for the higher grade students this lesson offers a wonderful opportunity to look into physics and chemistry behind the different dating techniques used to calculate the age of specimens from earth and the moon. Here is a cool radioactive dating game from PhET – simulations by the University of Colorado.
My favorite links to find more information:
Tree of Life: Yale Peabody Musuem of Natural History
Evolution Explained (Berkely)
Cladogram of Life (American Museum of Natural History)
5 lines of evidence for evolution - Mr. Sneideman’s blog
Great video:
My favorite naturalist and chronicler of life, David Attenborough, has a great series called First Life on the origins of early life by the BBC.

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