Gill Home


Michael Sharpe, Mathematics, UCSD and S. Gill Williamson, CSE, UCSD


(1) Click Grand Canyon (pdf) and Death Valley (pdf) in the Geo Charts List (right) to compare the structure of these two charts. Note where the information on the two charts are the same and different. Many of the items on these charts are hyperlinks. Explore these hyperlinks. Note the amazing amount of the earth's history that is represented by formations in Death Valley (over two billion years).

(2) Red text on a chart indicates that a formation from that time period can be found in the park or region. Non-red indicates no such formation is present (missing geology). Hyperlinks in red text should be specific to the park. Hyperlinks for the latter should be generic, common to all charts. We have found it difficult to get good park-specific hyperlinks in many instances so some such links are generic. Most generic links are to Wikipedia. Some are to Palaeos.

(3) The list of charts completed thus far is on the right side of this page. Printed out, these charts can be cut and folded to make a two-sided 4 x 6 card. This card can be used as bookmark (laminate it for durability). By the time you have finished the book you will have memorized much basic information about the earth's history!

(4) The arrow of time on each chart is the green arrow that contains the names of the Hadean, Archean, and Proterozoic eons (right panel) and the Paleozoic, Mesozoic, and Cenozoic eras (left panel). All of these names are hyperlinks. The Phanerozoic Eon is at the bottom of the left panel. These websites undergo changes from time to time. If you have problems go to their home pages (2) above.

(5) At the bottom of the left panel of each chart is a link to the UC Museum of Paleontology. This site is excellent for beginners and young students.

Geo Charts List

Anza-Borrego CA
Big Bend NP
Bryce Canyon NP
Death Valley NP
Grand Canyon NP
Torrey Pines SNR
Zion NP


The earth is about 4.54 billion years old, and geological time is divided into four eons with approximate start and end times as follows: Hadian (4.5 - 3.8 Ga), Archean (3.8 - 2.5 Ga), Proterozoic (2.5 - .542 Ga), and Phanerozoic (.542 Ga - present) where "Ga" means "billion years ago."

The official source for geologic time is GSA Geologic Time Scale. You should refer to this site for the latest information on geologic time at all levels of subdivision.

The Phanerozoic Eon (bottom of left panel) is divided into three eras, the Paleozoic, Mesozoic, and Cenozoic which are further subdivided into periods. The Cenozoic periods are further divided into epochs. There are two ways of dividing the Cenozoic into periods (1) Quaternary, Tertiary and (2) Paleogene, Neogene.




Cenozoic: Mammoths in background and foreground: (background) (foreground)

Both sources public domain art.The contextual art for the mammoths was drawn by S. Gill Williamson with Adobe Illustrator. This artwork is intended to be public domain.

Cenozoic: Mammoths Crossing Ice Field

Mesozoic: Mike Sharpe got the images of Brachiosaurus and kid from the following: (Monster Hunters, Francis Rolt - Wheeler, Lothrop, Lee & Shepard Co., 1916, page 346 picture opposite: Brachiosaurus). Another image (a Stegosaurus) from the above book is at This source states that the copyright on this book (Monster Hunters) expired and was not renewed, at least in the US.

The contextual art for this scene was drawn by S. Gill Williamson with Adobe Illustrator and Photoshop. This artwork is intended to be public domain.


Mesozoic: Mama Brachiosaurus and kid (eating something he's not supposed to)


Paleozoic: Art done by S. Gill Williamson using Adobe Illustrator.

The cephalopod is imaginary, inspired generally by the web reference:

This artwork is intended to be public domain.

Paleozoic: Large Ordovician nautiloid cruising for a snack.


Proterozoic: Imaginary scene by S. Gill Williamson depicting volcanic activity near the end of the Cryogenian ice age near the end of the Proterozoic. Snow is a sample from an uncopyrighted photo taken by Don Smith (UCSD Mathematics) and given to us for this purpose.

This artwork is intended to be public domain.


Archean: Imaginary art by S. Gill Williamson depicting an Archean sea with stromatolites exposed on a sandbar at low tide. This representation of stromatolites is based on a small sample (one stromatolite plus surrounding sand) from an uncopyrighted photo of stromatolites taken at Shark's Bay, Western Australia, by Dr. David Wacey (University of Western Austrlia). Dr. Wacey gave us his stromatolite photo for use in this project.

This artwork is intended to be public domain.