Continental drift and plate tectonics

Continental Drift Modern scientists consider the age of the Earth to be around 4.54 billion years Over that time it has changed a great deal

< Geologic time scale. Time subdivisions and geologic ages in millions of years (Ma) are after the Geological Society of America 1999 Geologic Time Scale (image from Stoffer, 2006).

Continental Drift EON ERA PERIOD EPOCH The largest division of geologic time is the Precambrian era It is broken up by significant events in earths history.

MESOZOIC Cretaceous Dinosaurs become extinct; Rocky Mountains begin forming. Jurassic Atlantic Ocean begins to form between N. America & Africa. Triassic st dinosaurs; North America begins to separate from Africa.

Continental Drift

Wegener’s hypothesis was that all the continents were once joined together in a single landmass. Continental drift – The idea that the continents slowly moved over Earth’s surface.

Continental Drift

Evidence: _____Sequences similar types are found arranged in the same way.

Evidence:_________

Evidence for Continental Drift Fossils – any trace of an ancient organism that has been preserved in rock. Wegener could not provide a satisfactory explanation for the force that pushes or pulls the continents.

Evidence: _______ Same mountain ranges on different continents seemed to match

Evidence: Puzzle pieces All ____ continents fit together like a puzzle

…an alternate explanation? 1928: Arthur Holmes suggested fluids rise toward the crust, spread, and sink again. 1930: Wegner dies, unable to adapt Holmes’ idea to his theory.

Studying Surface Changes Constructive forces shape the surface by building up mountains. Destructive forces are those that slowly wear away mountains and, eventually, every other feature on the surface.

The Crust The crust is a layer of solid rock that includes both dry land and the ocean floor. Three main layers make up Earth’s interior: the crust, the mantle, and the core. Each layer has its own conditions and materials.

The Mantle Earth’s mantle is made up of rock that is very hot, but solid. The mantle is divided into layers based on the physical characteristics of those layers.

The Core The core is made mostly of the metals iron and nickel. It consists of two parts–a liquid outer core and a solid inner core.

Lithosphere Rigid, rocky outer layer of the Earth, consisting of the crust and the solid outermost layer of the upper mantle. It is divided into 7 major plates It extends to a depth of about 60 mi (100 km).

Athenosphere Zone of the Earth’s mantle lying beneath the lithosphere, believed to be much hotter and more fluid than the lithosphere.

So What caused everything to move in the first place?

__________ Currents Heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion. Convection – heat transfer by the movement of a heated fluid Convection currents – the flow that transfers heat within a fluid

Convection Currents in Earth Heat from the core and the mantle causes convection currents in the mantle. This drives plate movement

Sea-Floor Spreading? the sea floor spreads apart along both sides of a mid- ocean ridge as new crust is added to the ocean floor. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

Evidence for Sea-Floor Spreading Several types of evidence supported the theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

Subduction at Trenches In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle through deep-ocean trenches. Deep-ocean trenches are deep underwater canyons formed where the oceanic crust bends downward. Subduction – the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Growing an Ocean Because of sea-floor spreading, the distance between Europe and North America is increasing by a few centimeters per year.

How Plates Move The lithosphere is broken into separate sections called plates. The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates and thus the 7 continents. Scientific theory – a well-tested concept that explains a wide range of observation s Faults – breaks in Earth’s crust where rocks have slipped past each other

Plate Boundaries There are three kinds of plate boundaries: 1.divergent boundaries – valleys and trenches 2.convergent boundaries – mountains and volcanoes 3.transform boundaries. – earthquakes zones A different type of plate movement occurs along each type of boundary. Rift valley – a deep valley that forms along the divergent boundary

Plate Boundaries At the locations where two tectonic plates interact, a boundary between these plates exist. There are three types of boundaries that geologist observe. These boundaries are divergent boundaries, convergent boundaries, and transform boundaries.