Geologic Time Scale Infographic, Ray Troll Fossil Cliff

Key points from the drawing

• The drawing shows Earth’s history as a cliff of rock layers, oldest at the bottom and youngest at the top, packed with the fossils typical of each time.
• Three eras are labelled, the Cenozoic, Mesozoic and Paleozoic, split into 17 periods and epochs, with the Proterozoic and Archean eons below them.
• Two mass extinctions are marked: “T/K, big, big extinction” at the end of the Cretaceous and “T/P, gigantic extinction” at the end of the Permian.
• Dates are in millions of years ago, and the base reads “Earth forms 4.6 billion years ago”.
• Several dates are from an older version of the time scale. The table below gives the current figures.

Geologic time scale infographic in text

The column on the right of the drawing lists each unit with the date at its lower boundary, which is when that unit began. The last column adds the current start date from the sources listed [4] [8].

The bottom label puts Earth’s formation at 4.6 billion years ago. Wikipedia gives the age of the Earth as about 4.54 billion years, and the Hadean eon as starting 4,567 million years ago [4].

What the drawing shows

Ray Troll is an artist based in Ketchikan, Alaska, known for scientifically accurate and often humorous artwork [3]. The left side of his cliff is filled with fossils. The upper Cenozoic layers hold mammal skulls, jaws and leaves. The Mesozoic layers hold dinosaur skulls, including a large theropod and a crested duck billed dinosaur, along with ammonites. The Paleozoic layers hold early fish, crinoids, a sea scorpion and trilobites near the base. The Precambrian layers at the bottom are bare, since complex fossils from that time are rare. A pterosaur flies past, and on top of the cliff fossil hunters dig beside a blue pickup truck loaded with finds.

The drawing is not to scale. The three Precambrian eons cover about 88% of Earth’s history but take up only the thin bottom bands. The Phanerozoic, the eon of visible animal life that the cliff mostly shows, spans about 538.8 million years, around 11.8% of the total [4].

How the time scale is divided

The US Geological Survey explains that Earth’s history is divided into eons, eons into eras, eras into periods and periods into epochs [5]. The names carry clues: “zoic” refers to animal life, “paleo” means ancient, “meso” middle and “ceno” recent, which gives the order Paleozoic, Mesozoic, Cenozoic [5]. The Pennsylvanian and Mississippian on the drawing are the two subperiods of the Carboniferous. The split comes from North American stratigraphy, where they were once treated as full periods [8].

The two extinctions marked on the drawing

The “big, big extinction” is the Cretaceous to Paleogene event, formerly called the Cretaceous to Tertiary (K to T) event, about 66 million years ago. It wiped out about three quarters of plant and animal species, including all non bird dinosaurs [6]. The “gigantic extinction” is the Permian to Triassic event around 251.9 million years ago, Earth’s most severe known extinction. It killed an estimated 81% of marine species and 70% of land vertebrate species [7].

Notes on this infographic

• Older dates. Several boundaries are from an earlier edition of the time scale. The Pleistocene now starts at 2.58 million years ago, after a 2009 revision, not 1.8 [8]. The Cambrian base was revised from 541 to 538.8 million years ago in 2022 and is shown here as 542 [4]. The Holocene began about 11,700 years ago, not 10,000 [8].
• Later edition. A newer version of this drawing, signed by Ray Troll and shared by Science Acumen in 2023, uses updated dates such as 2.6 for the Pleistocene and 66 for the Paleocene [1].
• Missing eon. The Hadean, the first of the four eons, is not labelled [4].
• T/K label. The “T” stands for Tertiary, a name now replaced by Paleogene and Neogene, which is why the event is now called K to Pg [6].

Questions about the geologic time scale

How many eons are there?

Four: the Hadean, Archean, Proterozoic and Phanerozoic [4]. This drawing labels only the Archean and Proterozoic, with the Phanerozoic shown as its three eras.

What are the three major eras?

The Paleozoic, Mesozoic and Cenozoic, the three eras of the Phanerozoic eon and the three labelled on the drawing [5].

Which part of the time scale holds 88% of Earth’s history?

The three eons before the Phanerozoic, the Hadean, Archean and Proterozoic, together often called the Precambrian. They span about 4,028 million years, roughly 88.2% of Earth’s history [4].

Sources

1. Science Acumen on Facebook, This Geologic Time Scale drawn by Ray Troll, 19 August 2023 (a later, signed edition of the drawing).
2. Ray Troll, trollart.com, read via Wayback Machine snapshot of 3 January 2025.
3. Wikipedia, Ray Troll.
4. Wikipedia, Geologic time scale.
5. US Geological Survey, Fossils, Rocks, and Time, The Relative Time Scale.
6. Wikipedia, Cretaceous to Paleogene extinction event.
7. Wikipedia, Permian to Triassic extinction event.
8. Wikipedia articles for each unit, used for the current dates in the table: Holocene, Pleistocene, Pliocene, Miocene, Oligocene, Eocene, Paleocene, Cretaceous, Jurassic, Triassic, Permian, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician, Cambrian, Proterozoic, Archean.

Last reviewed 29 October 2026