Environmental Sciences Course Earth Sciences Lecture 3 Week 2

1. Environmental Sciences CourseEarth Sciences Lecture 3 Week 2

2. Contents • The formation of the Earth • The structure of the Earth • micro plates • Rocks, minerals, and geologic structures • Solar Radiation University Of Palestine ENVI005

3. Formation of the Earth - Among the nine planets in the solar system, Earth is the only one which is known to support life. - All the materials we use are taken from the Earth and it supplies us with everything we eat and drink. - It receives energy from the Sun, which drives its climates and biological systems. University Of Palestine ENVI005

4. Formation of the Earth - The oldest rocks, found on the Moon, are about 4.6 billion years old and this is generally accepted to be the approximate age of the Earth and the solar system generally. - There are several rival theories describing the process by which the solar system may have formed. University Of Palestine ENVI005

5. Formation of the Earth - The most widely accepted theory, first proposed in 1644 by René Descartes, proposes that the system formed from the condensation of a cloud of gas and dust, called the ‘primitive solar nebula’ (PSN). - It is now thought this cloud may have been perturbed by material from a supernova explosion. Fusion processes within stars convert hydrogen to helium, In larger stars go on to form all the heavier elements up to iron. University Of Palestine ENVI005

6. Formation of the Earth Elements heavier than iron can be produced only under the extreme conditions of the supernova explosion of a very massive star, and the presence of such elements (including zinc, gold, mercury, and uranium) on Earth indicates a supernova source. University Of Palestine ENVI005

7. Formation of the Earth - As the cloud condensed, its mass was greatest near the centre. This concentration of matter comprised the Sun, the planets forming from the remaining material in a disc surrounding the star, and the whole system rotated. - The inner planets formed by accretion. Small particles moved close to one another, were drawn together by their mutual gravitational attraction, and as their masses increased they gathered more particles and continued to grow University Of Palestine ENVI005

8. Formation of the Earth At some point it is believed that a collision between the proto-Earth and a very large body disrupted the planet, the material re forming as two bodies rather than one: The Earth-Moon-System. University Of Palestine ENVI005

9. Formation of the Earth This explains why the Earth and Moon are considered to be of the same age and, therefore, why lunar rocks 4.6 billion years old are held to be of about the age of the Earth and Moon. University Of Palestine ENVI005

10. As it exists today, the Earth has: a mean radius of 6371 km Equatorial circumference of 40077 km Polar circumference of 40009 km Total mass of 5976× 1018ton mean density of 5.517 g. cm-3 Land 149× 106 km2 (29 %) Glaciers ice sheets 15.6× 106 km2 (3%) Oceans and seas 361× 106 km2 (69%) The structure of the Earth University Of Palestine ENVI005

11. The structure of the Earth University Of Palestine ENVI005

12. The structure of the Earth - At its centre, the Earth has a solid inner core, 1370 km in radius, made from iron with some nickel. - This is surrounded by an outer core, about 2000 km thick, also of iron with nickel, but liquid, although of very high density. - Movement in the outer core acts like a self- exciting dynamo and generates the Earth’s magnetic field. University Of Palestine ENVI005

13. The structure of the Earth • - Outside the outer core, the mantle, made from dense but somewhat plastic rock, is about 2900 km thick • at the surface there is a thin crust of • solid rock, about 6 km thick beneath • the oceans and 35 km thick (but less • dense) beneath the continents. University Of Palestine ENVI005

15. Questions?! University Of Palestine ENVI005

16. micro plates On Earth, but possibly on no other solar-system planet, the crust consists of blocks, called ‘plates’, which move in relation to one another. The theory describing the process is known as ‘plate tectonics’ (GRAHAM, 1981). University Of Palestine ENVI005

17. micro plates At present there are seven large plates, a number of smaller ones, and a still larger number of ‘micro plates’. The boundaries (called ‘margins’) between plates can be constructive, destructive, or conservative. University Of Palestine ENVI005

18. micro plates University Of Palestine ENVI005

19. micro plates constructive margins two plates are moving apart and new material emerges from the mantle and cools as crustal rock to fill the gap, marked by a ridge. There are ridges near the centers of all the world’s oceans. destructive margin Where plates move towards one another there is a destructive margin, marked by a trench where one plate sinks (is sub ducted) beneath the other. University Of Palestine ENVI005

20. micro plates conservative margins At conservative margins two plates move past one another in opposite directions. There are also collision zones, where continents or island arcs have collided. In these, all the oceanic crust is believed to have been sub ducted into the mantle, leaving only continental crust. Such zones may be marked in various ways, one of which is the presence of mountains made from folded crustal rocks. University Of Palestine ENVI005

21. micro plates An island arc is a series of volcanoes lying on the side of an ocean trench nearest to a continent. The volcanoes are due to the subduction of material. Slowly but constantly the movement of plates redistributes the continents carried on them. University Of Palestine ENVI005

22. micro plates University Of Palestine ENVI005

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24. Rocks, minerals, andgeologic structures Igneous Rocks Rock that forms from the cooling and crystallization of molten magma is called ‘igneous’, from the Latin igneous, ‘of fire’, - All rock is either igneous or derived from igneous rock. This must be so, since the molten material in the mantle is the only source for entirely new surface rock. University Of Palestine ENVI005

25. Rocks, minerals, andgeologic structures • If the magma reached the surface before cooling the rock is known as ‘extrusive’; if it cooled beneath the surface surrounded by older rock into which it had been forced, it is said to be ‘intrusive’. • Intrusive rock may be exposed later as a result of weathering. It is not only igneous rocks that can form intrusions. University Of Palestine ENVI005

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27. Rocks, minerals, andgeologic structures Sedimentary Rocks Sedimentary rocks are formed by deposition of either clastic sediments, organic matter, or chemical precipitates (evaporites), followed by compaction of the particulate matter and cementation during diagenesis. University Of Palestine ENVI005

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