The Formation of Rocks and Bedrock

1. Tectonic Plates
The tectonic plates move relative to each other due to the convection currents in the underlying mantle layer, causing earthquakes and volcanic eruptions along the plate boundaries, where they collide or slide beneath one another. The tectonic plates in the lithosphere float on the heavier rocks of the mantle. The Earth has one large long-term natural satellite, the Moon.

2. The Bedrock of Finland
The glacial periods may have lasted for up to tens of millions of years, and the thickness of the ice sheets may have been several kilometres. During the Weichselian glaciation, the glacier reached its maximum extent around 25,000 years ago.
The glacial periods cost Finland many of its interesting deposits, but the ice also revealed layers residing deep in the bedrock, generally difficult to access. Now these intrusive rocks can be extracted for durable, high-quality building stone and beautiful migmatites. The most recent glacial period largely eroded away the uppermost layers of the Finnish bedrock. Durable intrusive rocks, such as granite, were revealed underneath.
Finland’s bedrock used to be located near the equator. From there, the Fennoscandian Shield has drifted along the Earth’s crust to its current location. At the same time, it has transformed into its current shape and size due to the collisions and ruptures in the surrounding tectonic plates. As the plates collided, fold mountains were also created. Two of these ancient mountain ranges can be seen in Finland: the Karelides are a mountain range running from Eastern Finland to Lapland that formed around 2 billion years ago. The Svecofennides ran through Southern and Central Finland. They were folded somewhat later, around 1.9 billion years ago.
The Finnish bedrock is primarily old and worn away by erosive forces. The effects of the most recent glacial period can be seen in the bedrock: the uppermost deposits have largely been eroded away and the layers that normally reside deep in the Earth’s crust are visible. These layers consist of intrusive rocks, which have been created deep in the crust, in slowly cooling magma chambers. Intrusive rocks are hard and durable, making them excellent building stone material. Granite is one type of intrusive rock.

3. The Oldest Rock Gneiss
A piece of the world’s oldest known rock. This tonalitic gneiss (quartz-diorite gneiss) contains a mineral called zircon, enabling the radiometric dating. The dating revealed the mineral to be 3862 +/–3 million years old. This gneiss comes from an island in the Acasta river, flowing in the Northwest Territories of Canada.