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Hello
I'm writing this blog on 'Geology' for my 4th year Environmental Studies class.

Complete History of Ireland

Around 600 million years ago, what today is Ireland lay in two halves down near where North Africa now is. At this time Ireland lay beneath a tropical sea, which allowed layers of sand and mud to build up on the sea floor, forming sandstone and mudstone. As the North American and European continental plates collided, Ireland's two halves united and buckled to form several fold mountains, e.g. the Wicklow Mountains. The sedimentary rocks that had been resting on the sea floor were put under great heat and pressure, turning them into metamorphic rocks. The mudstone turned to slate and schist, while the sandstone became quartzite. The lava which came to the surface during this collision cooled and turned to granite, an igneous rock. Granite, slate, schist, and quartzite are today the most common rocks to be found around the fold mountains created in this collision. Elsewhere in Ireland, other sedimentary rocks (most notably Limestone, formed when layers of decaying sea creatures built up and compressed) and Igneous rocks can be found.

At this stage (around 400 million years ago) Ireland was above sea level, near the equator. Plants and land-animals lived on the land in this period. Most of Europe then sank underwater again. Many tropical reefs grew, forming limestone in the centre of the country. As the water level fell again, swamps and forests flourished, with their remains forming coal. This coal and much limestone was eroded as Ireland rose further out of the water and was carried North by continental drift.

The next time Ireland was submerged (about 200 million years ago) it was no longer in an area that could support tropical reefs. This sea left behind large chalky deposits on Ireland's landscape. Around 65 million years ago Ireland became a volcanic land, with many volcanic mountains, such as the Mourne mountains, forming.

From 25 million years ago to present, Ireland began assuming it's current position and climate, with erosion creating our current landscape.

This picture roughly shows the journey that Ireland has taken over the last half a billion years. A and B united at the multicoloured dot before drifting upwards.


















Picture from http://geography.about.com/

Rock types

There are three different categories of rock, Sedimentary, Igneous, and Metamorphic.

Sedimentary rocks are formed when layers of sediment build up on top of each other and compact under their own weight. Limestone is made of compacted fossils, Sandstone is made of compacted sand, an Mudstone is made of compacted soil.

Igneous rocks are formed when lava seeps up from the mantle of the earth and cools. These rocks cool into crystal shapes. If they cool quickly, the rocks form into large crystals like the basalt in the Giants Causeway. If the rocks cool slowly, they will contain small crystals, like the granite found in the Wicklow mountains.

During the collision of continental plates, Igneous and Sedimentary rocks can be subjected to great heat and pressure. This then changes them into other, harder, stronger rock types known as Metamorphic rocks. For example, the Sedimentary Mudstone could change under much heat and pressure into Shale, Slate, then Schist. The tectonic collision could also fuse different rock types together. For example, Schist and Mica could form to create Mica-Schist, which is abundant in the Wicklow mountains.


























This photo shows the relationship between the three different rock types.

Photo from http://www.nj.nrcs.usda.gov/partnerships/envirothon/soils/images/rockcycle.gif

The Arctic Treeline

My next post has little to do with my chosen topic of Geology, although it has everything to do with Geography. I am going to write about the Arctic Treeline.

A Treeline/Timberline is a line on a map past which trees are unable to grow because of the environmental conditions. There are several types of treeline:

Alpine Treeline - A line past which trees cannot grow because the land is too high up. The air pressure, temperature or terrain is unsuitable. Alpine treelines are found circling mountains, etc.

Desert Treeline - A line around a piece of dry land, which cannot support trees because of a lack of rainfall, or water from other sources.

Exposure Treeline - Strong winds or other forces found near the edge of islands, can create an area of land unsuitable for trees near coasts.

Others - Other factors such as unsuitable soil near volcanoes or high altitudes where condensation is incapable of occurring can lead to treelines. The specific treelines I'm going to talk about are the Arctic and Antarctic treelines.

Beyond these lines trees cannot grow because not enough light reaches the land, and the growing season (if it exists at all) is too short. The Antarctic treeline is actually only theoretical, as no trees grow on the Antarctic continent anyway, and the land to the north (South America, Australia, etc) has no treeline, so the 'Antarctic Treeline' doesn't exist.

The Arctic Treeline however is very real and exists in Greenland, Canada, Alaska, Russia, Finland, Norway, and Sweden. It is an approximately mile wide line in most locations, completely circling the North Pole, with a radius of around 2,600km. Although the transition between forests and tundra is gradual and subtle within this mile-wide line, from a small distance away the line is well defined. Beyond the line the trees cannot grow for the following reasons:

- Not enough light reaches the trees, therefore photosynthesis (and growth) cannot occur.

- The extremely cold temperatures freeze the sap inside the trees, killing them.

- The thin soil on top of the constantly frozen 'permafrost' cannot support trees.

- Strong winds can carry small shards of ice that can cut and kill trees. In this way, arctic winds have shaped the treelines in Russia and Canada.

- The required temperatures of at least 10°C during the growing seasons are not present.

- The trees above this line can become completely coated with snow, reflecting all light.

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The Arctic has not always been incapable of supporting tree life. At a different time, with a different climate, huge forests covered the North pole. These 40m tall trees have been found, perfectly preserved in the ice, less than 700 miles from the Pole.

So why am I interested in this strange topic, well I believe it is fascinating to think that it would be possible to fly a helicopter high over this greatly defined line, and see on one side a sprawling green woods, stretching for thousands of miles, with a barren Arctic tundra on the other. I have included several pictures and a map of the treeline.

Photos from:
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4XS2F6G3zm0RJR9rX5Yb-IF66hncab-kXgDvbStqS5asI0gwt-_VeIVIipEhTdQV2iYqmLgjdm3CDdysTXVhMPPm5m7wy-M0VRx_XGMTQqxbVD6-5SSe6rYkqMciMplsWyd9CSSgyO1g/s1600-h/Arctic+Treeline.gif
and
http://cache.virtualtourist.com/2500290-Aurora_Treeline_One_of_my_first_aurora_pictures-North_Pole.jpg

The Formation Of The Earth

This video explains how the Earth was formed and how plate tectonics work.

Northern Lights

Again, this has little to do with Geology, but I found some great pictures of the Northern Lights (Aurora Borealis/Aurora Australis) on http://en.wikipedia.org/wiki/Aurora_(astronomy).