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Three billion years of earth history

Scotland's oldest rocks formed some 3 billion (3,000 million) year ago which is a very long time ago! Comprehending the immensity of the time it has taken for Scotland to form - the immensity of geological time - is not easy.

A brief history of geology

The first person to suggest how vast a stretch of time we have to comprehend, was Scottish gentleman farmer and geologist James Hutton (1726-1797). Hutton realised that several cycles of sediment deposition; burial; heating, compression and folding; and re-exposure through erosion, must have occurred to account for the rocks formations he observed in Scotland. He also realised that these cycles would each take thousands or even millions of years. His studies lead to the observation that there is 'no vestige of a beginning, no prospect of an end' to the processes which formed rocks in the past and are still forming them today.

Eons, epochs and ages

These days, radio-isotope dating has allowed us to begin to quantify the depths of geological time, and the internationally agreed geological timescale allows us to correlate rocks and geological events world-wide. The timescale divides geological time into Periods and also larger divisions (Eras and Eons) and sub-divisions of time-Periods (Epochs and Ages). The current geological Period, the Quaternary, began 2.6 million years ago with the start of the most recent Ice Age. In contrast, the well-known Jurassic Period ('Age of the Dinosaurs') spanned a much larger time than the current Quaternary, lasting from 200 million years ago to 145 million years ago. Other geological periods are similarly of various different lengths, their starts and ends defined by factors such as global or regional change in environment or mass extinction events.

Fossil records

One very important geological boundary is that at the start of the Cambrian period (542 million years ago). This is the point, in the geological record, where life-forms with hard body-parts (e.g. shells) first appear. As hard body-parts, unlike soft ones, preserve well as fossils, this is the point at which our main fossil record begins. Because we get a lot of our information about past environments and geological time from fossils, the start of the Cambrian period is defined as the start of the Phanerozoic Eon or 'Known Time'. Geological time before the Cambrian period is often referred to simply as the Precambrian.

Hutton leading the way

Hutton's observations and theories marked the birth of the science of modern geology. They paved the way for later geologists to unravel the breathtaking tale of how Scotland has been 3 billion (3,000 million) years in the making. Study of the Earth as it is today, with its volcanoes and glaciers has been key in understanding Scotland's 3 billion year history. However, the truly ancient history of our country, the evidence for which is all around us, is crucial in helping us to understand our world today and predict how it will change tomorrow.

Last updated on Monday 14th December 2015 at 09:41 AM. Click here to comment on this page