Post the Geological Times

Quick Answer: Post the Geological Times is a geological time scale poster that sets out the divisions of Earth’s history, from eons and eras down to periods, in their correct order with the ages that separate them. Earth-science and biology teachers use it when teaching rock dating and the fossil record.

Reading a Chronostratigraphic Chart

The geological time scale is the calendar geologists use for the 4.6 billion years of Earth’s history. It is built as a ladder of nested units: eons are split into eras, eras into periods, and periods into epochs, with the oldest units at the bottom, just as the oldest layers lie at the bottom of an undisturbed rock sequence. A poster of this kind shows that ladder with boundary ages in millions of years, so students can place any rock or fossil in its interval at a glance.

The names on the scale carry information. Cambrian, Ordovician and Silurian come from the Latin name for Wales and two tribes who once lived there; Jurassic comes from the Jura mountains; Cretaceous from the Latin word for chalk. Boundaries are not arbitrary either: many mark changes in the fossil record, such as the end-Permian and end-Cretaceous mass extinctions. Teaching those links turns the chart from a list to memorise into a record of events.

Boundary ages are revised from time to time as dating methods improve, so a printed chart shows the values current when it was designed. In class, the order of the units and their approximate ages are what matter.

Specifications

Care & Handling

• Hang the time scale vertically if its layout allows, so the older units sit at the bottom like rock strata.
• Place it where students can read the smaller epoch labels without climbing on stools.
• Keep it clear of radiators and damp walls, which make paper posters ripple.

Applications

• Placing rock specimens and fossils from the school collection in their period during practical sessions
• Teaching the principle of superposition and how index fossils correlate layers between sites
• Locating the first fish, land plants or mammals in time during lessons on evolution
• Revising period names in order, for example with a mnemonic the class invents

Why Choose LabEquip

Earth-science teachers often display this scale beside the History of the Earth poster so events can be matched to named periods. Both belong to the Educational Charts range, and questions about either can be sent through the LabEquip contact page.

Frequently Asked Questions

What is the difference between an eon, an era and a period?

They are ranks of the same time scale. An eon is the largest unit, such as the Phanerozoic; it is divided into eras such as the Mesozoic; eras are divided into periods such as the Jurassic. Periods are split further into epochs.

How do geologists know the ages printed on the chart?

Numerical ages come mainly from radiometric dating of volcanic rocks, which measures the decay of radioactive isotopes. The order of events comes from relative dating, using superposition and fossils to decide which layers are older.

What is an index fossil?

It is a fossil of an organism that was widespread but lived for only a short span of time, such as certain ammonites or trilobites. Finding it in a rock layer lets geologists assign that layer to a narrow interval on the time scale.

Why do some period boundaries coincide with extinctions?

The scale was first drawn from changes in fossils between rock layers. Sudden losses of many groups, such as the end-Cretaceous extinction that removed the non-avian dinosaurs, created sharp breaks that geologists used as boundaries.

Does the poster show the Precambrian in detail?

The Precambrian covers most of Earth’s history but has few fossils, so time scale charts often compress it into a narrower band than the Phanerozoic. Check how your syllabus treats the Archean and Proterozoic when using the chart.

How can students get a sense of deep time from the chart?

Convert the scale into a length, for example one metre of corridor for every hundred million years, and mark events along it. Students then see that the whole of human history occupies a tiny fraction of the final step.

Last Updated: September 2026