Chapter 12 Thermal Energy Transfer Drives Plate tectonics
What is thermal energy Thermal energy with respect to plate tectonics is energy of molten rock that is constantly moving below your feet. Below the surface of the earth, there are plates that are constantly moving by the movement of this churning melted rock. This movement may cause plates to move in opposite directions, and bring those plates together cause major geological events such as volcanic eruptions and earthquakes
Evidence for Continental Drift 12.1
Continental Drift There is quite a bit of evidence that suggests that all of the continents were once all joined together but later drifted to their current locations Evidence for this includes o o Coasts of the continents can be aligned Regions that are far apart have similar rocks, mountain ranges, fossils and paleoglaciation
Continental Drift The process of sea floor spreading provides a mechanism for continental drift Each continent is attached to a huge slab of rock known as tectonic plates When these tectonic plates move, they carry continents with them
The continents of the world have not always been in the same place...
Continental Drift Theory Alfred Wegener... The continents have drifted to their present locations over millions of years. They were once joined as a supercontinent (Pangaea)
Pan - gaea all Earth
Putting the Pieces Together... The continents do not fit perfectly like a jigsaw puzzle. A better fit is found by matching the continental shelves (original shorelines that are now underwater)
Matching Geological Structures & Rock Evidence Mountain ranges of one continent, end at coastline begin again at another continent (similar folds, ages)
Geological/ Rock Evidence Similarities between rocks of adjacent continents are evidence for continental drift. The rocks found in Newfoundland are the same type and age as rocks found in Greenland, Ireland, Scotland, Norway.
Matching Fossils The fossils of some ancient species suggests evidence for pangaea. Wegener found fossils of a fresh-water reptile Mesosaurus in two places: - SE South America and SW Africa
This small freshwater reptile could not have swam this distance.
Fossil Evidence Glossopteris (a fern) Found In: South America Africa Australia India Antarctica
Fossil Evidence Problem: Ferns do not grow in cold climates (Antarctica)
Glacial Evidence Evidence of glaciers formed in ice ages provides support to CD theory During ice ages, glaciers covered large areas of land
Paleoglaciation When the glaciers retreat/ advance, they leave behind proof o Deeply scratched rocks (striations), U-shaped valleys, patterns of rock formations Paleoglaciation refers both to the extent of ancient glaciers and to the rock markings they have left behind.
Paleoglaciation Scientists were puzzled by evidence of glaciers in places that are now tropical, like India and Africa! If they were at one time connected, this would make sense.
More Evidence Coal Deposits in Antarctica - Coal forms from dead matter (usually tropical swamp material) - Since the South Pole has never had a tropical climate...it must have been in a warmer location than it is now
How the Continents Moved & a Possible Mechanism The current theory is that the continents moved due to the movement of tectonic plates. Tectonic plates = movable slabs of rock that make up the Earth
Tectonic Plates These large rigid plates slide over the surface of Earth (over a layer of partially molten rock) magma partially molten surface Tectonic plates explain the location of volcanoes and earthquakes...
Volcanoes/ Earthquakes Volcanoes are openings in the Earth s surface that spew gases, chunks of molten rock Earthquakes are sudden, ground-shaking releases of built up energy under Earth s surface
Earthquake zones and volcanoes follow a pattern... They occur along the boundaries (edges) of tectonic plates (form an outline)
Mid-Atlantic Ridge Mapping of the ocean floor revealed a long mountain range running down the middle of the Atlantic Ocean. It is called the Mid-Atlantic Ridge
How it was formed... The tectonic plates of the Earth slide apart (sliding is called conduction ) Another way to think of this is seafloor spreading Something must replenish this lost crust! Occurs at rate of ~ 1 inch /yr
Magma to the Rescue!!!! Areas of oceanic crust are replenished by volcanic activity... o o o Magma (molten rock) rises up Cools and hardens when it reaches surface Forms the new sea floor
Magma and More Magma This process keeps going... o o o Convection currents cause more magma to rise Magma forces apart hardened material Older rock is pushed aside as new rock forms! Sea Floor Spreading
Animation... Spreading Ridge
Proof of Sea Floor Spreading! In the 1940 s...oceanographers took samples of rock from the Mid- Atlantic Ridge - Younger rocks were found closer to ridge - Older rocks were found farther from ridge (and in thicker layers...built up!)
More evidence in the rocks!! Scientists have also found that the rocks themselves have a striped pattern To understand this, we must understand the Earth s magnetism...
Earth s Magnetic Field Every few thousand years...the direction of magnetic field REVERSES! MAGNETIC REVERSAL
Consider a rock... Rock contains metals like iron (Fe) Little pieces of iron line up with magnetic field and then they STAY that WAY! When MAGNETIC REVERSAL happens...they line up in opposite direction! Rocks preserve the direction of the Earth s magnetic field that existed when the rock formed! Amazing!
Studying the magnetic properties of ancient rocks... Paleomagnetism
Back to the Sea Floor... So the sea floor is spreading and new rocks (from magma) are formed... Looking closely at the sea floor, scientists found a striped pattern! Normal magnetic polarity Reverse magnetic polarity magnetic striping
A HOT SPOT... A geological area where molten rock rises to Earth s surface! In mid-1960 s, Canadian geologist J. Tuzo Wilson suggested that chains of volcanic islands were formed when a tectonic plate passed over a stationary hot spot. Developed plate tectonic theory...unifying theory of geology.
HOT SPOTS... Hawaiian Islands were formed by a tectonic plate passing over a hot spot. The plate slides in the direction of the arrow... Forms a CHAIN of islands!