Introduction to rocks Dr P Allen

The Principles of Geologic Science Fundamental to geology is the principle of Uniformitarianism Definition? The scientific law stating that the geological processes taking place in the present operated similarly in the past and can therefore be used to explain past geologic events James Hutton ( ) supernatural theories were not needed to explain the geologic history

Principle of Uniformitarianism Uniformitarianism allows us to interpret rocks, however it is in the PRESENT that many geological processes are discovered, observed and analysied: Application of modern observation to ancient rock = Actualism The present is the key to the past

The Present is the Key to the Past Great Phrase but not strictly correct – Why? Because not all events of the past have been duplicated or observed within the Human time span Did a asteroid cause the extinction of the Dinosaurs? Did the impact inject dust into the upper atmosphere to cause a nuclear winter? Or was it something we have not Considered? Because some details remain Unclear actualism does not apply

James Hutton ( ) Sir Charles Lyell ( ) Principles of Geology Fathers of Modern (Scientific) Geology After a long debate they changed the view Of the Scientific community and rejected a theory called Catastrophism Both thought the Earth was ever changing BUT retained its basic features By applying THEIR principles we know this to be untrue!

Mothers of Geology She sells sea-shells on the sea-shore, The shells she sells are sea-shells, I'm sure For if she sells sea-shells on the sea-shore Then I'm sure she sells sea-shore shells. Mary Anning ( ) Mary Anning's first Plesiosaur

Materials and Processes of Geology ROCK? Rocks consist of interlocking or bonded grains of matter which are typically composed of minerals Minerals Naturally occurring inorganic solid element or compound with a particular chemical composition or range of compositions and a characteristic internal structure Quartz (Silicon dioxide Si04) most common mineral on the face of the Earth. It is found in nearly every geological environment and is at least a component of almost every rock type

Nature and Origin of Rocks Basic Rock types -How Many?Igneous, Sedimentary and Metamorphic Intrusive formed below surface but eventually exposed at surface Rock broken down by Weathering – weathered rock is transported to a site and accumulates as sediment Igneous rocks form when magma crystallizes and solidifies. The melt originates deep within the Earth and are divided into two groups, intrusive or extrusive (volcaneos), depending upon where the molten rock solidifies.

Sedimentary Rocks Where does sediment accumulate? How does it become solid? Deserts, rivers, slopes, beaches, seafloors, lakes, Lithification – the process of sediment becoming solid rock The grains of sediment become mutually attached by compression of the sediment after burial. The sediment may be glued together by precipitation of mineral cement from watery solutions that flow through the sediment. 1. Clastic –Sandstone - Conglomerates

Sedimentary Rocks (cont) 2. Biogenic 3. Chemical

Metamorphic Rock Where does metamorphic rock come from? How does it develop? Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot, mineral-rich fluids or, more commonly, some combination of these factors Marble (non foliated) Gneiss (foliated)

Igneous Rocks Extrusive igneous rocks – Hardens at the Earth’s surface Intrusive igneous rocks – Hardens within the Earth

Rock Cycle Multiple cycle within the “rock cycle” Intrusive relationships Component relationships

Geologic Time Scale Developed using – Biostratigraphy (fossil succession) – Radioactive decay Divided into – Phanerozoic – Precambrian/Archean Cambrian – Oldest rocks with conspicuous fossils