The science of Geology Geology is the science that pursues an understanding of planet Earth Physical geology - examines the materials composing Earth and the processes generating them Historical geology - seeks an understanding of the origin of Earth and its development through time; chronology of events

Geologic time Accurate dates to events in Earth history Absolute dating Relative dating and the geologic time scale Relative dating means that dates are placed in their proper sequence or order without knowing their age in years The magnitude of geologic time Involves – millions or billions of years Geological processes operate –Gradually over periods as much as millions of years –Episodic in events that may last only seconds to minutes

Geologic time scale Age in millions of years

Early evolution of Earth Origin of planet Earth Earth and the other planets formed at the ~same time from interstellar dust Nebular hypothesis Layered structure developed by chemical segregation early in the formation of Earth

A view of Earth Earth’s four spheres Hydrosphere Atmosphere Biosphere Solid Earth

Earth as a machine Internal forces Powered by heat from the interior Leads to convection in the earth Moves plates on the earth surface Produce volcanoes, earthquakes, and mountains External forces - Powered by the Sun that drives external processes in the Atmosphere Hydrosphere At Earth’s surface

Earth’s surface has two principal divisions Continents Ocean basin

The workings behind the scene Surface features, like oceans, mountains and others, are the product of internal workings of the earth

Earth’s internal structure “Layercake” Earth Crust continental oceanic Mantle upper lower Core outer inner

Mechanical Subdivision of the upper Earth Lithosphere (rigid) Asthenosphere (ductile, plastic) Mesosphere Earth’s internal structure

Earth’s Surface Earth’s crust broken into rigid plates 7 major plates Where plates meet are called plate boundaries Three types of plate boundaries

Plate Boundaries Divergent (constructive) boundary – plates move apart, resulting in upwelling of material from the mantle to create crust Convergent (destructive) boundary – plates move towards each other; subduction of oceanic plates or collision of two continental plates Transform (conservative) boundary – plates move along each other without either generating new lithosphere or consuming old lithosphere

Dynamic Earth The theory of plate tectonics Theory, called plate tectonics, has now emerged that provides geologists with the first comprehensive model of Earth’s internal workings The theory of plate tectonics Involves understanding the workings of our dynamic planet Began in the early part of the twentieth century with a proposal called continental drift – the idea that continents moved about the face of the planet

The loop that involves the processes by which one rock changes to another Illustrates the various processes and paths as earth materials change both on the surface and inside the Earth The Rock Cycle

There are three rock classes Igneous (magmatic) rocks Sedimentary rocks Metamorphic rocks

formed from a magma through crystallization either at or beneath the surface examples: lava flows, granite, basalt, pumice Melting Magma Cooling + Crystallization Igneous rocks Lava Igneous Rocks

Sedimentary Rocks formed through deposition of solid particles or through precipitation examples: sandstone, claystone, limestone Deposition or Precipitation Cementation + Compaction (Lithification) Sedimentary rocks Sediment Transport

Metamorphic Rocks formed through metamorphic transformation due to heat and pressure examples: schist, slate, marble Heat + Pressure (Metamorphism) Metamorphic rocks Compression Heat

The science of Geology Some historical notes about geology The nature of Earth has been a focus of study for centuries Catastrophism – earth changes by large events like floods, eruptions, etc. Uniformitarianism – present is key to past; processes same through time, only rates have changed

The nature of scientific inquiry Science assumes the natural world is consistent and predictable Goal of science is to discover patterns in nature and use the knowledge to make predictions Scientists collect “facts” through observation and measurements

The nature of scientific inquiry How or why things happen are explained using a Hypothesis – a tentative (or untested) explanation Theory – a well-tested and widely accepted view that the scientific community agrees best explains certain observable facts

The nature of scientific inquiry Scientific methods Scientific method involves gathering facts through observations and formulation of hypotheses and theories There is no fixed path that scientists follow that leads to scientific knowledge