Continental Drift / Plate Tetonics - Zoogeography Notes / Textbook

Significance of the continental drift theory

With the exception of the theory of evolution, continental drift theory has had the biggest contribution to biogeography.

plate tectonics theory

explains the origin and destruction of the Earth’s plates as well as their lateral movement or drift.

Alfred Wegner

A German meteorologist that conveyed and championed the theory of continental drift starting in 1910.

• Died on an expedition to Greenland where he was attempting to prove his theory with research

Wegners important conclusions relating to continental drift:

• Sial vs. Sima: Continental rocks (sial – rich in silicon and aluminum) are less dense, thicker, and less magnetized than oceanic rocks (sima – rich in silicon and magnesium). Continents (sial) float on a layer of viscous, fluid mantle.

• Pangaea: Earth’s major landmasses were once united in a single supercontinent, Pangaea. It broke into smaller continental plates that drifted apart. North America remained connected to Europe in the north until the Neogene or even the Quaternary.

• Rift Valley Origin of Oceans: The breakup of Pangaea began with rift valleys that widened into oceans. Mid-ocean ridges and oceanic trenches formed where continents once joined. Earthquakes and mountain building are related to block movement.

• Matching Continents: Continents have mostly retained their original outlines. Their matching margins, stratigraphy, fossils, and paleoclimates show they were once connected, contradicting the idea of fixed continents and ocean basins.

• Rates of Continental Drift: Landmasses move between 0.3 and 36 meters per year. Greenland may be the fastest, possibly separating from Europe only 100,000–50,000 years ago.

• Radioactive Heating: Radioactive heating in the mantle may drive block movement, but other forces are likely involved. These processes are gradual, not catastrophic.

Wegener’s theory was unique in the sense that it utilized information from a variety of disciplines, including:

geology, geophysics, paleoclimatology, paleontology, and biogeography.

tillites

Sedimentary rocks formed from glacial till, consisting of unsorted mixtures of clay, sand, gravel, and boulders deposited directly by glaciers. They provide evidence of ancient glaciation in the geologic record.

Issues with Wegener’s theory:

• He and most scientist as the time assumed the Earth was much younger than it actually want. To compensate for this idea, he suggested that the continent’s move at relatively incredibly high speeds. This was not very plausible, however with the discovery that earth is over 4 billion years old, his theory began to make more sense with an adjusted rate of drift.

• His theory did not present a plausible mechanism during his time. Not until many years later was this proven.

Mid Oceanic Ridge System

• Wegener said that mid oceanic ridges indicate where opposing continents were once joined

• Radioactive heating in the mantle is likely a primary cause of the movement of crustal plates

  • Drive convection currents

Evidence for plate tectonics / Cont Drift

• Stratigraphic evidence

• Paleoclimatic Evidence

• Fit of continental margins

• Unique fossils distributions

• Paleomagnetism evidence

Stratigraphic Evidence (for continental drift):

Topographic and geological features—such as mountains, oceanic ridges, island chains, rock strata, Precambrian shields, and fossil deposits—match up across now-separated continents. These similarities support the idea that continents were once connected in the supercontinent Gondwana.

Paleoclimatic Evidence (for continental drift):

Late Paleozoic glacial deposits (tillites) are found in the southernmost regions of all southern hemisphere continents. Glaciers left deep scratches in the rocks that show their direction of movement. When these glacial paths are mapped, they only align logically when the continents are reassembled as they were during the Permian period, supporting the theory of continental drift.

seamounts

peaked submarine volcanos

guyots

flat topped structures

Organisms that have a shared common ancestor from pangea across many continents….

then developed unique speciation and evolutions after periods of separation

Paleo

a really long time ago

Pollen records….

are a good indicators of time and can be found in lake sediments

Paleomagnetism (and continental drift):

Studies of paleomagnetism provided additional evidence for seafloor spreading. Rocks record the direction and declination of Earth's magnetic field at the time they formed, allowing scientists to reconstruct the past positions of continents.

Remnant Magnetism:

As molten rock cools, iron and titanium oxides in the rock align with Earth's magnetic field. This alignment is preserved ("frozen") in the rock's crystal structure and can be measured to determine the relationship of landmasses to the magnetic poles when the rock formed.

Earth’s Magnetic Field Generation:

Convective flows of molten material from inside Earth’s core, and through its mantle, generate magnetic fields that permeate the planet.

Pangea

A supercontinent that existed during the late Paleozoic to early Mesozoic eras, roughly 335 to 175 million years ago. It included almost all of Earth’s landmasses joined together.

Breakup: Pangaea began to split during the early Jurassic Period.

Two major pieces it broke into:

• Laurasia (northern part – includes North America, Europe, Asia)

• Gondwana (southern part – includes South America, Africa, Antarctica, India, Australia)

genus

generic (a bunch of genera)

glaciation

A period when large parts of Earth's surface were covered by glaciers or ice sheets. It involves the advance and retreat of ice due to long-term climate changes and plays a major role in shaping landscapes and influencing sea levels and ecosystems.

• It’s happened many times in Earth’s history

Roughly how much do landmasses move each year?

10ish cm / year

Over the course of Earth’s history, what has happened to the tilt of the Earth on its axis?

• The tilt angle has changed slightly over time. These slight variations are enough to directly impact changes in climate, temperature, seasons, and length of days on Earth. All of which would have affected the distributions of species.

What occurred between the Paleozoic and Mesozoic?

there was a major glaciation

Ice scours

gauges in bedrock causes by glaciation, and serves as an indicator of which way the glacier was moving.

Tillite

loose materials dug up by glaciers moving that eventually form sedimentary rock

tille

loose materials dug up by glaciers that form tillite.

galaxoid fishes

freshwater fishes that are found on different continents, but they could not have survived cross the ocean, so they must have a common ancestor that dates back to a time where landmasses were connected

paleomagnetism (poles)

• Positive and negative charged poles

• when igneous rocks solidify and contain iron, they become oriented to the Earth’s magnetic field, like a compass.

magnetometer

tool used to estimate direction and distance to nearest magnetic pole

• The igneous rock must be attached to the Earth’s crust where it formed in order to get a reading

Seafloor Spreading and Magnetic Polarity

• As new oceanic crust forms at mid-ocean ridges, it records Earth's magnetic field as it cools.

• Earth’s magnetic field reverses over time between normal polarity (green stripes) and reversed polarity (brown stripes).

• These magnetic "stripes" are symmetrical on either side of the ridge, proving the seafloor spreads outward.

• The names (Gilbert, Gauss, Matuyama, Brunhes) refer to different time periods of magnetic polarity over the past 4 million years.

• This pattern confirms the theory of seafloor spreading, first proposed by Harry H. Hess in 1962.

Current model for plate tectonics

• sea floor spreading

• Forces driving continental drift

• Forms of plate boundaries

• A concise history of drifting continents from the mesozoic era to near the present

Spreading centers have alot of…

volcanic activity

Oceanic crust is more dense than terrestrial crust which means…

Significance:
Because oceanic crust is denser, when it collides with less dense continental crust, it sinks beneath it into the mantle in a process called subduction. This leads to:

• Formation of deep ocean trenches

• Creation of volcanoes and mountain chains

• Recycling of crustal material back into the mantle

So, it's the greater density of oceanic crust—not less—that drives subduction.

3 forces that push continental drift

• ridge push

• mantle drags

• Slab pull

Plate Movement (Cause):

Lateral movements of plates result from a complex interaction among Earth's crust, mantle, and core—especially heat in the core that drives plate movement.

Lithosphere:

The outer shell of Earth, made of thick, rigid plates composed of a relatively thin, rigid layer of crust and upper mantle.

Asthenosphere:

A deeper, more fluid layer beneath the lithosphere, composed mainly of molten rock that allows tectonic plates to move.

Ridge Push:

Occurs at mid-ocean ridges where molten rock wells up from the asthenosphere, pushing older rock outward and driving seafloor spreading.

Mantle Drag:

Lateral flow and friction between the mantle and overlying plate creates a dragging force, like a conveyor belt.

Slab Pull:

As dense oceanic plates are subducted, their weight pulls the rest of the plate with them toward the subduction zone. This may generate most of the plate motion force

Slab Pull Importance:

Modeling suggests slab pull may account for more than 90% of net tectonic forces driving plate movement.

Plate Boundaries

:
Earth’s plates meet at three main types of boundaries:

• Divergent Boundaries: Plates move apart (spreading zones)

• Convergent Boundaries: Plates collide (subduction zones)

• Transform Boundaries: Plates slide past one another (strike-slip faults)

Tectonic Phenomena:

Events like earthquakes, volcanism, and mountain formation are strongly linked to interactions at plate boundaries.

Himalaya Formation:

The Himalayas began forming about 60 million years ago when the Indian Plate drifted northward and collided with the Eurasian Plate.

Appalachian Mountains Formation:

Formed over 300 million years ago when North America collided with northwestern Africa. These are older and more eroded compared to the Himalayas.

Major Tectonic Plates:

There are seven major plates larger than 20 million km², including the Pacific, North American, Eurasian, African, South American, Antarctic, and Australian plates. There are also smaller plates like the Gorda and Juan de Fuca microplates.

Rift Zones:

On continents, divergent boundaries form rift zones—long linear fissures where land is pulling apart. Examples include the Red Sea and East African Rift Valley.

Seamount (Guyot):

A volcanic island formed at a mid-ocean ridge that sinks below sea level over time, becoming a flat-topped underwater mountain.

geomorphology

The scientific study of landforms and the processes that shape them, including weathering, erosion, deposition, tectonic activity, and glaciation. It helps explain the origin and evolution of landscapes on Earth’s surface. (trenches)

The west coast of South America is considered a…

Active / Subduction Zone

East coast of South America…

Passive Margin (East Side):

• No subduction or major tectonic activity

• Broad continental shelf

• Dominated by sediment accumulation

• Stable, with fewer earthquakes or volcanoes

• Example: Atlantic coast of South America

So, the east side is tectonically quiet, unlike the tectonically active west coast.

Western Cordillera

: A major mountain system along the western edge of the Americas, stretching from Alaska to the Andes. It includes several ranges such as the Rocky Mountains, Sierra Nevada, Cascades, and the Andes. Formed largely by tectonic activity at convergent plate boundaries, especially subduction zones, it is geologically young, tectonically active, and known for earthquakes, volcanism, and mountain building.

The Cascades (Cascade Range):

A mountain range in the Pacific Northwest of North America, extending from British Columbia through Washington and Oregon to Northern California.

• Formed by subduction of the Juan de Fuca Plate beneath the North American Plate

• Part of the Ring of Fire, known for active volcanoes like Mount St. Helens, Mount Rainier, and Mount Hood

• Composed mostly of volcanic peaks and igneous rocks

• Still tectonically active, with frequent seismic and volcanic activity

Mount Baker:

• Located in northern Washington State

• Part of the Cascade Range

• A glaciated stratovolcano formed by subduction of the Juan de Fuca Plate

• One of the most heavily glaciated peaks in the lower 48 U.S. states

• Still active, with fumaroles and geothermal activity

Mount St. Helens:

• Located in southern Washington State

• Famous for its 1980 eruption, one of the most powerful in U.S. history

• A stratovolcano in the Cascade Range, formed by subduction zone volcanism

• Continues to show seismic and volcanic activity today

• Known for its dome-building eruptions and volcanic hazards

Composite Cone (Stratovolcano):

A tall, steep-sided volcano built from alternating layers of lava, ash, and volcanic rock. Formed at convergent plate boundaries, especially subduction zones.

• Eruptions are often explosive and dangerous

• Made of andesitic to rhyolitic magma (viscous)

• Examples: Mount St. Helens, Mount Fuji, Mount Vesuvius

active volcanos are usually near subduction zones because…

magma is heterogeneous

Largest seafloor plate:

• Pacific Plate – It is the largest tectonic plate overall, covering most of the Pacific Ocean and a significant portion of the Earth's surface.

Smallest seafloor plate:

• Juan de Fuca Plate – One of the smallest oceanic plates, located off the northwest coast of North America. It's involved in subduction beneath the North American Plate and contributes to volcanic activity in the Cascade Range.

Indo-Malayan Archipelago:

A vast group of islands in Southeast Asia, located between the Indian and Pacific Oceans. It includes countries such as Indonesia, the Philippines, Malaysia, Brunei, East Timor, and Papua New Guinea.

• Part of the Ring of Fire, with high volcanic and seismic activity

• Formed by complex tectonic interactions, including subduction zones and island arcs

• One of the world’s most biodiverse regions, both marine and terrestrial

• Also known as the Malay Archipelago or Maritime Southeast Asia

island arc

forms parallel to a subduction zone (caused by northern movement of austrailia)

Nazca Plate:

An oceanic tectonic plate located in the southeastern Pacific Ocean, off the west coast of South America.

• It is subducting beneath the South American Plate along the Peru-Chile Trench

• This subduction is responsible for forming the Andes Mountains and causing frequent earthquakes and volcanic activity

• Moves eastward at a rate of several centimeters per year

• Plays a major role in the tectonic activity of the South American west coast

• Moving towards SA

Mesozoic Era (252–66 million years ago) and continental drift are closely linked:

• Breakup of Pangaea: The supercontinent Pangaea began to break apart during the early Mesozoic, especially in the Jurassic Period.

• It split into Laurasia (north) and Gondwana (south), leading to the formation of modern continents.

• Atlantic Ocean began to open, creating new ocean basins.

• This era marks the beginning of modern plate tectonics, with continents starting to drift toward their present positions.

• The distribution of fossils and similar rock formations across now-separated continents supports this drift during the Mesozoic.

K-T Boundary (Cretaceous–Tertiary Boundary):

A geological marker dating to about 66 million years ago, marking the mass extinction event that wiped out the dinosaurs and many other species.

• Now officially called the Cretaceous–Paleogene (K–Pg) boundary

• Identified by a thin layer of iridium-rich clay found worldwide

• Likely caused by a massive asteroid impact (e.g., Chicxulub crater in Mexico)

• Marks the end of the Mesozoic Era and the beginning of the Cenozoic Era

Stasis and Plate Movement

:
Tectonic plates often remain still (stasis) for long periods, followed by sudden movement, causing earthquakes and sometimes tsunamis, such as the 2004 Indian Ocean tsunami.

Pangaea:

A supercontinent that existed around 335–200 million years ago, made up of nearly all landmasses. It eventually split into Laurasia (north) and Gondwana (south).

Gondwana:

The ancient southern supercontinent composed of South America, Africa, Madagascar, Arabia, India, Australia, Antarctica, and surrounding regions. It existed as early as 850–800 million years ago.

Laurasia:

The northern landmass formed from parts of Pangaea, including North America, Europe, and Asia. It separated from Gondwana in the Mesozoic Era.

Breakup of Pangaea:

Started around 200 million years ago, near the end of the Triassic. It led to evolutionary isolation and diversification of species on different continents.

Panthalassa:

The global ocean that surrounded Pangaea during the late Paleozoic and early Mesozoic eras.

Island Arc:

A curved chain of volcanic islands formed by subduction of one oceanic plate beneath another (e.g., Aleutian Islands).

Seamount (Guyot):

An underwater volcanic mountain that once rose above sea level but has since subsided and flattened at the top due to erosion.

Breakup of Gondwana:

Initial rifting began around 160 Ma, with regions like Madagascar and New Zealand separating from Antarctica and India. Later, India split from Madagascar (~130 Ma) and drifted rapidly north to collide with Eurasia around 40 Ma.

Breakup of Laurasia

By 75 Ma (Late Cretaceous), Laurasia fragmented. A new land bridge formed between western North America and eastern Eurasia, allowing for biotic exchange via the Bering Strait (Beringia).