This text is read through and edited by  Doctor Tore Prestvik, NTNU, Institutt for geologi og bergteknikk:

Scientists estimate that the universe formed in a large explosion called the Big Bang, between 15 and 20 billion years ago.
The Earth formed ca. 4.6 billion years ago. The molten rock eventually cooled and a hard outer crust was formed. The Earth became stratified into three main layers that are called the core, the mantle and the crust. The heaviest elements sank to the core while the lighter elements became concentrated in the Earth’s crust. The temperature increases towards the center of the Earth and the matter behaves more plastically. The inner core is solid and probably consists of iron and nickel. The outer core is also made of iron and nickel but is molten. For the most part, the mantle behaves plasitcally except for the uppermost mantle, which is solid. This outermost mantle, taken together with the crust, make up the lithospheric plates that move around the Earth’s surface. When two plates colide, a mountain chain is formed (like the Himalayas). When the plates move apart, ocean basins are formed (like the Atlantic). The oceans have a thin crust while the continental crust (like under Norway) is much thicker. Where there are tall mountains, a root (made of the lithosphere itself) extends down into the mantle, just like an iceberg floating in the water. Likewise, the lithosphere is thinner where depressions or basins exist.

The island of Leka is composed mostly of serpentinite and gabbro (the main compenents of the Leka Ophiolite Complex). Serpentinites dominate the west side; these are made of the mineral serpentine and the remains of the olivine and pyroxene from the original dunite and harzburgite (rocks from the upper mantle made of olivine and pyroxene). Gabbro is the main rock on the south and east sides. Gabbro is made of olivine, plagioclase and pyroxene. The picture shows the serpentinite hills.

Picture taken of Dr Rolf Birger Pedersen, UiB 1999.

The Leka Ophiolite Complex is 497+/- 2 million years old. The age was determined by examining weak radioactive minerals in the silica-rich lavas.

Later, the complex was eroded down to sea level and sedimentary rocks were deposted on top. These were later folded and lithified to the conglerates, sandstones, marbvles and shales we see today. They are found in a belt from Gangstøen, through Leka Camping, past Havna and north on the eastern side of Skeisnesset.

In this area of Norway where continental bedrock dominates, The Leka Ophiolite Complex is an exotic remnant of oceanic material. In some places the old continental bedrock breakes the surface. On the mainland (Gutvik/Austra), granitic gneiss is the main rock type. These rocks are ca. 1800 million years old and formed when granites undergo high stresses or temperatures.

The sedimentary rocks deposited in continental basins or on the continental shelf were folded during the Caledonian orogeny as well. On Solsemøyene we find this type of sedimentary rock. The rocks that were shoved deepest became so warm that they melted partially. There were also intrusions from melt from the mantle. This magmatic material formed intrusive rocks like granites, syenites and gabbros. In Horta, we find all three of these rock types together with metamorphosed sedimentary rocks. There are also granites on Sklinna.

On the path up to the Solsem Cave, we find what might be the country’s youngest rock - a conglomerate that is approximately 10,000 years old. It is formed by cementing loose grains and gravels to make a conglomerate and was formed after the last Ice Age.