12.1 Evidence for Continental Drift Flashcards
Who proposed the idea of continental drift?
German scientist Alfred Wegener
What is the Continental Drift Theory?
A theory that states that the continents have not always been in their present locations but have “drifted” there over millions of years.
What was Wegener’s first piece of evidence?
South America’s eastern coastline and Africa’s western coastline surprisingly fits well.
What’s the name for the giant land mass?
Pangaea
What else supported Wegener’s idea?
His analysis of rocks and mountains ranges.
Explain Wegener’s analysis of rocks and mountain ranges
- mountain ranges appear to continue on different continents
- similarities between rock structures are found on different continents
Other than rocks and mountain ranges, what else matches?
Fossils
What are glaciers
Vast masses of ice
Where are glaciers found
At the poles and high in the mountains
When glaciers retreat, what do they leave behind?
They leave behind large U-shaped valleys, deeply scratched rocks, and various types and patterns of rock formations.
Define paleoglaciation
The extent of ancient glaciers and to the rock markings they left behind.
What evidence does coal deposits in Antarctica give?
Coal usually forms from the decomposition of tropical swamp animals, and Antarctica certainly isn’t a tropical place. It suggests that Antarctica was once in a warmer location.
What was the problem of Wegener’s theory?
He couldn’t prove how the continents could move
Define tectonic plates.
The large slabs of rock that form Earth’s surface, moving over a layer of partly molten rock.
Define volcanoes.
Openings in Earth’s surface, that, when active, spew out gases, chunks of rock, and melted rock.
Define earthquake.
A sudden, ground-shaking release of built-up energy at or under Earth’s surface.
Where do earthquakes and volcanoes usually occur?
At the boundaries between tectonic plates.
What is the Mid-Atlantic Ridge?
A mountain range in the Atlantic Ocean.
Where are the youngest rocks usually found on the ocean floor?
Close to the ridge.
Define Ocean Sediment
The small particles of silt and organic debris deposited on the ocean floor.
What is the relation of the ocean sediments and the ridge?
The further away from the ridge, the thicker the sediments are.
Define magnetic reversal.
The process in which Earth’s magnetic field, over thousands of years, completely reverses its direction.
What are the scientists’ thoughts on how magnetic reversal happened?
They think that Earth’s magnetic field is produced by the motion of liquid iron in the planet’s interior. If the motion of this material changes, Earth’s magnetic field changes as well.
Define paleomagnetism.
The study of the magnetic properties of ancient rocks.
What device do oceanographers use to survey the magnetic polarity across the bottom of the Atlantic Ocean?
They use a magnetometer, it detects variations in magnetic fields.
Define magnetic striping.
A strange pattern of stripes in the direction that iron-containing materials pointed on the sea floor.
Who proposed an explanation that tied together data on the age of ocean rocks, sediment thickness, and magnetic striping?
Harry Hess, geology professor
Define magma.
Molten rock from beneath Earth’s surface.
What does Henry suggest about the magma?
He suggested that the magma rises because it’s less dense than the material around it. The magma cools, than hardens after breaking through Earth’s surface at a spreading ridge.
What forms new sea floor?
Cooled down magma.
Define spreading ridge.
The region where magma breaks through Earth’s surface, continually forcing apart old rocks and forming new sea floor.
What causes more magma to rise, and sea floors to split apart?
Convection currents.
Define convection current.
The movement of a fluid caused by density differences.
What does the new magma do?
It forces apart the hardened material and continuously pushes older rock aside.
What is all that process called?
Sea floor spreading! :)
How were the Hawaiian Islands formed?
When a tectonic plate passes over a stationary hot spot.
What’s a hot spot?
An area where molten rock rises to Earth’s surface.
Who released a scientific paper that combined the concepts of sea floor spreading and paleomagnetism to explain continental drift?
Canadian geologist J. Tuzo Wilson
What did Wilson’s hypothesis explain?
It explained the formation of mountains and ocean basins and the cause of earthquakes and volcanic eruptions.
What is Wilson’s theory also called?
Plate Tectonic Theory
