GCSE AQA Chemistry :The Changing World

Earth is SPHERICAL (radius 6400km) & made up of layers:                                                                                                                                                           1. CRUST: At surface, thin and solid. Thickest 70km, thinnest under oceans (5km)                                

2. MANTLE: Under crust, half way to center of earth (3000km thick),almost entirely solid but can flow very slowly.

3. CORE: Dense and made of metals (nickel and iron),outer core liquid, inner solid.

- Scientists used to think mountains and valleys formed by shrinking (crust solidified as earth cooled down  then earth continued to shrink forming wrinkles)

4. LITHOSPHERE is Earth's crust and upper mantle.It is cracked into pieces called TECTONIC PLATES. - Mountains form at boundaries between plates.Huge forces push up the crust. Can cause volcanoes/earthquakes.          - Plates move a few cms each year. Natural radioactivity in Earth produces heat which creates convection currents in the mantle & move plates.

- Alfred Wegener 1915 proposed theory of continental drift but not accepted as a theory. why not?............in 1960's new evidence found on ocean floor and Weg's ideas used to develop theory of plate tectonics.

Most likely theory about earth's formation (4.5 billion yrs ago) & early atmosphere:                                                                                                        1. VOLCANOES released gases :CO2, H20 Vapour, Nitrogen.  

 2. As Earth cooled water vapour became OCEANS so atmophere was mostly CO2 (plus some water vapour and Nitrogen). May have been small amounts of Methane & Ammonia. NOO2 !                                                                                                                                                       

3. Algae & plants evolved. They used CARBON DIOXIDE for PHOTOSYNTHESIS & this released OXYGEN.(So CO 2 decreased and O 2 increased as plants increased)

LAST 200 Million yrs: Now main gases in atmosphere: Nitrogen (78%) and Oxygen (21%) (4 fifths/1fifth)                                                                        Other gases c 1% are NOBLE gases (mainly Argon) CO 2 and water vapour.Most CO2 in early atmosphere ended up in rocks & fossil fuels.     NOBLE GASES = Grp 0 of periodic table.LEAST REACTIVE ELEMENT. used where lack of reactivity impt. ARGON used in an inert atmospehere (eg light bulbs),NEON electrical tubes for advertising, HELIUM in balloons.

The Carbon Cycle maintains the levels of Carbon Dioxide in the atmosphere.

CO2 moves in and out of the atmosphere naturally. This has been kept in BALANCE for millions of years.

1. Plants remove CO2 to produce food via PHOTOSYHNTHESIS

2. CO2 is release back in - plants and animals RESPIRE or DECOMPOSE

3. Some carbon is used to make animal shells, in past they formed sedimentary rock. Carbon in plants and animals also went into fossil fuels

4. Volcanoes decompose carbonate rocks that have moved deep in ground to produce CO 2

BURNING fossil fuels releases CO 2 which had been absorbed from the atmosphere millions of yrs ago.COMBUSTION of fossil fuels has increased dramatically in last 50 yrs  (relative to time it took took to form) resulting in more CO 2 in atmosphere.

As the amount of CO 2 increases, more DISSOLVES in oceans.