2.1 - Geological Timescale
The purpose and structure of the geological timescale
The geological timescale is a framework used to categorise and understand the vast history of the Earth, which spans billions of years.
Understanding the geological timescale
The Earth's history is split into distinct segments known as geological periods. These periods are defined by major occurrences, such as the formation of particular rock types or notable shifts in climate and life forms.
Key geological periods and their timelines
Geological periods cover vast stretches of time, dating back hundreds of millions of years.
Timeline of major geological periods
The table below outlines the most recent geological periods and when they began, measured in millions of years before the present.
| Geological Period | Began, million years before present |
|---|---|
| Quaternary | 2.6 |
| Tertiary | 65 |
| Cretaceous | 145 |
| Jurassic | 215 |
| Triassic | 245 |
| Permian | 285 |
| Carboniferous | 360 |
| Devonian | 410 |
| Silurian | 440 |
| Ordovician | 505 |
| Cambrian | 585 |
Formation of rocks in the UK during specific geological periods
Many of the rocks found in the UK today were formed millions of years ago under climatic conditions very different from the present.
Rock formations in the UK across geological periods
- Tertiary Period (65 million years ago) - Chalk was formed in the UK during this time, when much of the land was submerged under warm tropical seas.
- Jurassic Period (215 million years ago) - Clay deposits were created in the UK under warm and humid conditions.
- Carboniferous Period (360 million years ago) - Carboniferous limestone emerged in the UK under tropical conditions.
- Ordovician Period (505 million years ago) - Granite was formed in the UK during volcanic activity.
While these periods mark the primary times of formation for these rocks, some of these rock types also formed during other geological periods.
Comparison of geological time to human timescales
The immense scale of geological time is difficult to grasp when compared to human history.
Contrasting geological and human timescales
The Earth is estimated to be around 4,600 million years old. In contrast, humans have only been present for approximately the last 200,000 years. Geological time operates on a scale of millions and billions of years, making it vastly different from the human perception of time.