Earth's Resources : Geosphere

Earth's Resources : Geosphere - Key SQA Definitions

• Weathering - The exposure and breaking down of rocks in situ at the Earth’s surface over geological time due to interaction with the atmosphere.

• Transportation - The movement of rock fragments by water, wind, ice or gravity from the place where they were originally weathered.

• Erosion - The breaking down of rock fragments into smaller pieces and sediments due to collision with other rock fragments during transportation.

• Deposition - The settling out of rock fragments and sediments after transportation by water, wind, ice or gravity.

• Igneous - Rock that forms through the cooling of molten rock (magma) to a solid form in the upper crust or on the surface of the Earth.

• Sedimentary - Rock that is formed from weathered rock fragments and sediments that have been eroded, transported, deposited, compacted and cemented.

• Metamorphic - Rock that has been subjected to heat and/or pressure, permanently altering the minerals or internal structure.

• Rock - A solid mass made of one or more minerals.

• Mineral - An element or chemical compound formed as a result of rock cycle processes.

• Ore - A naturally occurring solid material from which a metal or valuable mineral can be extracted profitably.

• Porosity - A measure of a rock’s ability to hold fluid.

• Permeability - A measure of the amount of water allowed to pass through a rock.

The Geosphere

The geosphere consists of all of the Rocks and Minerals that make up the Earth. This incudes the material below the surface all the way down to the Earth's core, as well as surface rocks, mountains and beaches. The Geosphere also includes the abiotic parts of soil as well as the fossilised remains of organisms that died millions of years ago. 

There are several processes that form part of the Geosphere, with the processes collectively making up the 'Rock Cycle'.  

The Structure of the Earth

The Earth is an oblate spheroid (a sphere that is wider than it is tall) with a radius (distance from center to surface) of approximately 6400 km. It is due to the Earth's rotation that is is not fully spherical in shape.

The Earth rotates once every 24 hours (approximately) giving the Earth it's day and night cycle. The Earth orbits around the Sun once every 365.25 days, giving the length of one year:- 

As can be seen from the above simulation, the earth does not rotate vertically, its 'axis of rotation' is at an angle to the vertical, at 23.5 degrees to the vertical. It is this angle to the vertical that causes the Earth to have 'seasons':-

Below the Surface

The Earth's structure is split into three main sections:- 

• The Crust - The outermost layer of the Earth's structure and is made of solid rock, consisting mostly of basalt (the oceanic crust) and granite (the continental crust). The crust is the thinnest layer of the Earth's structure, with the continental crust about 40km thick and the oceanic crust only about 10km thick. 

• The Mantle - The mantle is largest layer of the Earth's structure (~2900 km thick), consisting of hot, dense, iron and magnesium-rich rock known as magma. The mantle acts like a viscous fluid, moving over geological time.  The movement of the mantle has caused the crust above to be broken into 'plates' which move over time in a process known as 'Plate Tectonics'.

• The Core - The core is the innermost layer of the Earth's structure and is made of a liquid outer core and a solid inner core. Both the inner and outer core are mostly a mixture of nickel and iron, and are responsible for generating the Earth's magnetic field.

Scientists cannot directly sample the inner structure of the Earth. The deepest hole ever drilled only reached a depth of 12,262 meters, less than half of the thickness of the continental crust. 

Scientists understand the structure of the Earth by analysis of seismic waves generated by earthquakes. As the seismic waves pass through the Earth, they are refracted or blocked by the changing density of material. By analysing the changes in the waves detected across the Earth, the structure of the Earth can be modelled:-

Plate Tectonics

Plate tectonics is the theory explaining the motion of the Earth's crust over geological time. Due to forces provided by gravity and the movement of the mantle below, the crust of the Earth is continually in motion, with plates moving apart, together or past each other. 

The diagram below shows the major plates that make up the Earth's crust, as well as their relative motion:-

The motion of the Plates is caused by rising convection currents within the Mantle pushing upwards on the crust forming ridges. 

These ridges get pushed apart, with new crust forming at the split. Due to the slope of the ridge, the older material gets dragged downhill due to gravity, pushing the surrounding crust away, this is known as 'Ridge Push'. 

At other plate boundaries, the more dense older crust sinks below newer crust (this location is known as a subduction zone) and again gravity drags the crust downwards, this time into the mantle in a process known as 'Slab Pull'. 

The video below shows how the movement of the Plates has affected the landforms of the Earth over the last 1.5 billion years:-

You would study the structure of the Earth and investigate mineral and energy resources. You’d do research to find ways to protect people who live in places with volcanoes and earthquakes. You’d research how the planet was formed and shaped over time. 

Depending what kind of project you work on, you would be invloved in engineering projects such as dams or tunnels, storage of nuclear waste, search of energy resources such as oil and gas or study earthqukes and volcanoes. 

The Rock Cycle

Just like the 'Water cycle' which describes how water changes state and moves through the environment, Rocks are not static but change over time through a variety of processes. 

The diagram below shows an overview of the processes that make up the Rock Cycle:- 

A description of any cycle can start at any point, but in this case the starting point will be taken as Magma, which is molten rock beneath the Earth's Crust. This magma is heated by nuclear reactions deep within the Earth, keeping it in a semi-solid state. 

When this magma rises towards the surface through convection, it pushes up through the solid crust above. Usually this magma cools below the surface and forms solid rock (see igneous rock below), but in special cases the magma can remain liquid long enough to break through the crust. These 'breaks' in the crust is known as  Volcanoes, and once the molten rock is on the surface, it is known as 'Lava'. 

As can be seen from the diagram, solid rock is classified into three key types:- 

Igneous Rock

Igneous Rocks are formed when molten rock cools. Different types form when the rock cools at different speeds. The faster the the rock cools, the smaller the 'grains' within the rock.

Sedimentary Rock

Sedimentary Rocks are formed when dust, small rocks and other minerals are deposited on the bottom of a river (or other bodies of water) and are compressed over time to form solid rock. These will usually show many layers when viewed in cross section. 

Metamorphic Rock

Metamorphic Rocks are formed when other types of rock are placed under high temperatures and pressures, usually at plate boundaries, changing their structure. 

Weathering

Weathering is the breaking down of rocks on the Earth's surface. There are three key ways that this can occur:-

Soil Formation

Soil is a very complicated material that is formed by the mixing together of the products of weathering (rocks, gravel, sediments etc.) with decaying organic matter (dead leaves and other plant material etc.). 

Erosion

Erosion is the process which occurs after weathering. After weathering, the resulting material (small rocks, gravel, sediment, dust etc.) can be transported to new locations. This is done either by the wind blowing the material, or by water washing the material away. 

Whilst being transported, the rock fragments are broken into smaller pieces and sediments due to collision with other rock fragments. 

This eroded material is then deposited (dropped)  somewhere new, usually forming sediments which can go on to make sedimentary rock if the conditions are correct. 

Rocks or Minerals? 

When describing the material, in everyday language, the words 'Rock' and 'Mineral' are used interchangeably. In this course, however, the difference between them is important:-

• Mineral - An element or chemical compound formed as a result of rock cycle processes.

• Rock - A solid mass made of one or more minerals.

These minerals can be broken up further into specific chemical compounds that they consist of:-

Extracting Useful Metals and Minerals from Rock

The rocks that make up the Earth's crust contains many valuable metals and minerals, that can be used to create the wide range of materials. However, for these to be used, they first must be separated from the rest of the rock itself. 

If a rock contains enough of a valuable metal or mineral that it can be extracted to make a profit, then that rock is known as an 'Ore'. 

Some examples of Ores are shown below:-

Mineral Case Study : Haematite (Iron Ore)

Iron is one of the most common elements in the Earth's crust. We turn it into the alloy steel and use it for construction, cars, cutlery, surgical instruments and more... 

Iron ores formed billions of years ago in the early oceans. In the oceans of the early Earth, there was lots of iron present, but almost no oxygen. When the earliest life evolved in the oceans, oxygen was expelled as a waste gas of the process of photosynthesis. 

This dissolved oxygen reacted with the iron in the water to form iron oxides, which settled to the bottom of the oceans. These iron oxides became part of the sediment, and then became part of the resulting sedimentary rocks. 

The image below shows a 'banded iron formation', sedimentary rock showing layers of iron-rich ore between layers of other minerals:-

The mining of iron ore is a major global industry, with 2.4 billion tons of iron ore extracted in 2017 alone:-

Mining of iron ore is most commonly done using the 'open pit' mining method. In 'open pit' mining, the surface material (rock, vegetation, soil etc.) is removed by giant excavators to expose the layers of ore below. The ore is then extracted by blasting (explosives used to break up the rock) and then removed and transported to a processing site. Once the mining is completed, the surface material and non-ore material (known as 'overburden') is returned to the site and landscaped to repair as much of the site as possible. 

An example of open pit mine reclamation work can be seen in the north-east of England. The excess overburden from the Shotten open pit coal mine has been shaped into the "world's largest sculpture of the human form", named 'Northumberlandia'. The sculpture consists of 1.5 million tons of material removed as part of the mining process and is over 400m long, creating a public park from the remnants of the mining process:-

Once the iron ore has been mined and transported to a processing facility, the iron can then be extracted from the ore. In order to extract the iron from its ore, a Blast Furnace is used. The blast furnace combines the iron ore with the mineral lime (from limestone) and coke (a form of carbon) to extract the pure iron:

The video below shows the process of the extraction of iron from its ore:-

There are three key outputs from the Blast Furnace:- 

With further processing, the iron produced in a blast furnace can be used in a huge variety of ways. 

Mineral Case Study : Limestone

Limestone is a type of Sedimentary Rock that is composed of more than 50% calcium carbonate. Limestone forms in shallow tropical sea water as a result of calcium carbonate precipitating out of a dissolved state, either by biological or non-biological means. 

In warm tropical water, there is a large amount of dissolved calcium carbonate. Several processes can cause this dissolved calcium carbonate to form a precipitate (to for an insoluble solid from a dissolved substance). These include temperature changes, simple physical movement of the water and also biological action, in the form of exoskeleton or shell making. 

Limestone is quarried (mining for rocks or minerals for construction) either in an 'open quarry' (most commonly) or a 'subsurface quarry':-

Limestone has a huge range of uses, from cut blocks used in construction, as a raw ingredient in cement making, or (if processed further into Quicklime or Slaked Lime) a wide range of chemical uses:- 

Cement Manufacturing is a major use of limestone globally with 3.3 billion tons of limestone was quarried for the global cement industry in 2004. Cement is made by combining ground limestone with sand and clay, then heating the mixture in a kiln before being mixed with gypsum. 

Cement making is a major contributor to Climate Change due to the emission of carbon dioxide in the production process, The cement making industry accounts for 7% of the global carbon dioxide emissions globally in 2017, mostly through the calcination process :-

As part of reducing carbon dioxide emissions, the cement industry is now having to look at changes that can be made in order to stay within carbon emission targets:-

The graph below shows how the cement industry could cut their emissions across cement production by 75% in order to keep within climate targets:-

Limestone also plays a part in controlling the amount of carbon dioxide in the Earth's atmosphere, by being a 'Carbon Sink', a way to store carbon out of the atmosphere over geological time periods. 

Mineral Case Study : Crude oil

Crude oil is a mixture of many different hydrocarbons. Hydrocarbons are chemical compounds that contain the elements carbon and hydrogen only. Crude oil forms over millions of years from dead animal remains which have been buried under many layers of sediment on the ocean floor:-

Once the crude oil (and natural gas) is formed it fills the gaps within porous rock. A porous rock is a rock that can hold a liquid or gas within it in small gaps within its structure. If the rock is also permeable (liquid or gas can pass through it) then the crude oil rise through the rock (as it is less dense than the surrounding water) until it reaches an impermeable layer of rock and becomes trapped. 

The diagram below shows the difference in terms of porosity and permeability of rock:-

These 'Petroleum Traps' are where oil collects together to form an oil (and gas) reservoir. Two of the most common 'Traps' are shown below:-

In order to extract the Crude oil (and natural gas) from these traps, drilling of Oil Wells is used. Oil wells are long holes drilled into the ground and through the impermeable rock layer to access the crude oil reservoir below. These can be both on land or out at sea and therefore require a range of technologies:-

When crude oil is removed from the earth it is found as a mixture of different sized liquid molecules. It can be separated into its different hydrocarbons by a process called Fractional Distillation. 

Fractional distillation separates a mixture into a number of different parts, called fractions. A tall fractionating column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points (small molecules) condense at the bottom and substances with lower boiling points (large molecules) condense on the way to the top:-

The fractions obtained from this process have a huge number of uses, not just in terms of fuels but as a raw ingredient of plastics (and other chemicals) and other products:-

The fossil fuels (crude oil, natural gas and coal) also play a part in controlling the amount of carbon dioxide in the Earth's atmosphere, by being 'Carbon Sinks' like limestone, storing carbon out of the atmosphere over geological time periods. This is why the use of these fuels is causing climate change, by returning the carbon to the atmosphere. 

In order to reduce this impact, new technologies are being developed that can mimic a carbon sink, known as  'Carbon Capture and Storage' or 'Geo-Sequestration':-

The hydrocarbons that make up crude oil are very damaging to the environment. Oil can kill animals and birds by poisoning or suffocation, as well as affecting buoyancy and natural waterproofing. 

Oil chemical contaminated food supplies can cause malnourishment and poisoning throughout the food web with the effects seen more in higher trophic levels due to biomagnification:-

The toxic chemicals released by oil spills remain in the ocean for years, often sinking down to the seafloor and poisoning the sediment which, if disturbed, can release the chemicals back into the water.

The diagram below shows the impact of an oil spill on a single group of animals - Sea Turtles:-

Environmental Impact Case Study : Deepwater Horizon  

On April 20, 2010, the oil drilling rig Deepwater Horizon, operating in the Gulf of Mexico, exploded and sank resulting in the death of 11 workers on the Deepwater Horizon and the largest spill of oil in the history of marine oil drilling operations.  

4 million barrels of oil flowed from the damaged well over an 87 day period, before it was finally capped on July 15, 2010.  

On December 15, 2010, the United States filed a complaint in District Court against BP Exploration & Production and several other defendants alleged to be responsible for the spill. 

BP settled the cases against them for an unprecedented $5.5 billion ( Clean Water Act penalty ) and $8.8 billion in Natural Resource Damages.