Greenland is famous for being the largest island in the world-but actually Greenland is sort of like a continent...
More than anything else, the geology of Greenland - the landscape of Greenland - has been and still is shaped by the great ice sheet.
Today Greenland's ice sheet covers more than 85% of the island. That means, just 15% of Greenland is not covered by ice.
Bedrock - the Precambrian
Earth's earliest rocks were formed some 4,500 to 570 million years ago! So long ago it is hard to grasp, this time is called the Precambrian period - and the rock is what is called bedrock.
Bedrock is the foundation on which Greenland is built. Almost all of southern Greenland is still bedrock today. Bedrock is made up of the two rock types: granite and gneiss.
In other areas of Greenland, over the long periods of time, other layers have been formed on top of this bedrock as a result of geological processes-changes to the landscape caused by events... at the Earth's surface, inside of Earth or off the Earth, like falling meteorites landing on Earth! Examples of event on Earth's surface are: weathering (breakdown of rock), landslides, and erosion by running water or glaciers! Events inside of Earth could be earthquakes and volcano eruptions!
The layers that cover the bedrock on Greenland can be lavas, or sediments - decomposed products such as clay and sand, or calcareous shells from small creatures, which are turned through time into shale, sandstone and limestone respectively as a result of pressure due to deep burial under later layers.
These sedimentary layers can be extremely thick, up to 6 miles (10 km) deep - but then in some places the layers are broken down again by erosion (wearing away of rock), so that it is now down to bedrock again!
Nowadays bedrock is actually the dominant rock type in the ice-free areas of Greenland!
Different Kinds of Bedrock
Not all bedrock is the same-because it was not all formed at the same time!
The oldest part - the ancient core - is found on the west coast between Paamiut and Kangerlussuaq. In a location northeast of Nuuk, bedrock has been dated as being at least 3,700 millions years old. That means it is the oldest of any rocks found on Earth!!
The youngest section of the ancient core is 'only' 2,500 million years old.
South of this area lies the younger bedrock, the Ketilidian. This is 1,800 to 1,500 milion years old.
North of the ancient core - right up to Qaanaaq - are the Nagssugtoqidian, formed during the same period as the Ketilidian.
Both the Ketilidian and the Nagssugtoqidian are made up of materials from the ancient core, so in reality it is all ancient core but done forming at different ages!
Bedrock only lies exposed in a few places in northern Greenland, where it has been covered by formations from later times.
While bedrock is mostly made up of the two rock types granite and gneiss, there are also other types of rock in bedrock. In many places in Greenland gneiss and granite walls have distinctive dark bands of another rock type: dolerite dykes! Delorite dykes happen when magma from the inside of earth forces its way upwards though cracks in the bedrock! Magma is fluid, very hot material (molten rock) located beneath earth's crust, inside of earth-the kind of stuff that comes out of a volcano: lava is a river of magma!
Explore the time before the Precambrian period - From Palaeozoic, to Mesozoic to Cenozoic
DID YOU KNOW...
The inner part of the ice cap is a single large unified sheet. But in many places out near the rim of the ice cap, crevasses 90-120 feet deep (30-40 metres) deep can be found. A crevasse, a crack in the ice sheet, most often comes to be because of ice movement over the underground terrain.
Out towards the rim mountain peaks stick up through the ice. In Greenland - and everywhere else - these are called nunataks.