Report in Oceanography

1. CONTINENTS
Ronniel Mark B. Delos Reyes
BSF III

2. Pangaea
• About 300 million years ago, Earth didn't have seven continents,
but instead one massive supercontinent called Pangaea, which was
surrounded by a single ocean called Panthalassa.
• The explanation for Pangaea's formation ushered in the modern
theory of plate tectonics, which posits that the Earth's outer shell
is broken up into several plates that slide over Earth's rocky shell,
the mantle.

3. • Scientist Alfred Wegener proposed the notion of an ancient
supercontinent, which he named Pangaea (sometimes spelled
Pangea), after putting together several lines of evidence.
• The "continents fit together like a tongue and groove.“

4. • Pangaea formed through a gradual process spanning a few
hundred million years. Beginning about 480 million years ago, a
continent called Laurentia, which includes parts of North
America, merged with several other micro-continents to form
Euramerica. Euramerica eventually collided with Gondwana,
another supercontinent that included Africa, Australia, South
America and the Indian subcontinent.

5. • About 200 million years ago, the supercontinent began to break
up.Gondwana (what is now Africa, South America, Antarctica, India
and Australia) first split from Laurasia (Eurasia and North America).
Then about 150 million years ago, Gondwana broke up. India peeled
off from Antarctica, and Africa and South America rifted, according
to a 1970 article in the Journal of Geophysical Research. Around 60
million years ago, North America split off from Eurasia.

6. Plate Motions and
Boundaries

7. Four Types of Plate Boundaries
• Divergent boundaries -- where new crust is generated as the plates
pull away from each other.
• Convergent boundaries -- where crust is destroyed as one plate
dives under another.
• Transform boundaries -- where crust is neither produced nor
destroyed as the plates slide horizontally past each other.
• Plate boundary zones -- broad belts in which boundaries are not
well defined and the effects of plate interaction are unclear.

8. Rates of motion
• The oceans hold one of the key pieces to the puzzle. Because the ocean-
floor magnetic striping records the flip-flops in the Earth's magnetic field,
scientists, knowing the approximate duration of the reversal, can calculate
the average rate of plate movement during a given time span. These
average rates of plate separations can range widely. The Arctic Ridge has
the slowest rate (less than 2.5 cm/yr), and the East Pacific Rise near
Easter Island, in the South Pacific about 3,400 km west of Chile, has the
fastest rate (more than 15 cm/yr).

9. Tectonic Activity
• Today, we know that the continents rest on massive slabs of rock
called tectonic plates. The plates are always moving and
interacting in a process called plate tectonics.
• The continents are still moving today. Some of the
mostdynamic sites of tectonic activity are seafloor spreading
zones and giant rift valleys.

10. • In the process of seafloor spreading, molten rock rises from within
the Earth and adds new seafloor (oceanic crust) to the edges of the
old. Seafloor spreading is most dynamic along giant underwater
mountain ranges known as mid-ocean ridges. As the seafloor grows
wider, the continents on opposite sides of the ridge move away from
each other.
• The North American and Eurasian tectonic plates, for example, are
separated by the Mid-Atlantic Ridge. The two continents are moving
away from each other at the rate of about 2.5 centimeters (1 inch) per
year.

11. Rift valleys are sites where a continental landmass is ripping itself apart.
Africa, for example, will eventually split along the Great Rift Valley
system. What is now a single continent will emerge as two—one on the
African plate and the other on the smaller Somali plate. The new Somali
continent will be mostly oceanic, with the Horn of Africa and Madagascar
its largest landmasses.

12. The processes of seafloor spreading, rift valley formation,
and subduction (where heavier tectonic plates sink beneath lighter ones)
were not well-established until the 1960s. These processes were the main
geologic forces behind what Wegener recognized as continental drift.