‫کیا تو نے نہ دیکھا کہ دریا میں کشتی هللا کے فضل سے‬

‫چلتی ہے تاکہ وہ تمہیں اپنی کچھ نشانیاں دکھائے بیشک‬

‫اس میں ہر بڑے صبر کرنے والے‪ ،‬بڑے شکرگزار‬
‫کیلئے نشانیاں ہیں ۔‬
‫‪Surah Luqman 31:31‬‬
 Origin of Oceans, Seas, and Ocean Floor

• The Earth’s oceans and seas formed over 4 billion years ago, soon after the
planet cooled. As volcanic activity released gases like water vapor into the
atmosphere, the vapor condensed into clouds, leading to millions of years
of rainfall. This rain filled Earth's low-lying basins, giving rise to the first
oceans and seas.

• At the same time, the ocean floor — the bottom surface beneath the water
— began to take shape through powerful geological processes. Plate
tectonics, volcanic eruptions, and sedimentation sculpted features such as
continental shelves, deep-sea trenches, mid-ocean ridges, and abyssal
plains.

• Over time, the ocean floor has continued to evolve, playing a key role in
Earth’s geology, climate, and life systems. Studying it helps us understand
not just the sea, but the planet itself
 Ocean floor profile
 The ocean floor profile refers to the cross-sectional view or structure of the
ocean bottom from the coastline to the deepest parts of the ocean.
 It shows the various physical features that lie beneath the ocean's surface,
similar to how a landscape profile shows mountains, valleys, and plains on
land.
1. Continental shelf
The continental shelf is the submerged, gently
sloping edge of a continental landmass, extending
from the coastline to the continental slope. It is the
shallowest part of the ocean floor and is geologically
part of the continent
 Depth: Usually extends to a depth of 0–200 meters.
 Slope: Very gentle gradient (about 0.1° on average).
 Width: Varies greatly — can be just a few kilometers wide (e.g., in the
Pacific Ocean) or over 1,000 km wide (e.g., off the Arctic coast of Siberia).
 Sediments: Covered by thick layers of sediments derived from rivers,
glaciers, and coastal erosion

Importance :
• ,Rich in nutrients and sunlight.
• Home to coral reefs, fisheries, and diverse marine life.
• Major zones for commercial fishing.
• Holds vast reserves of oil, natural gas, and minerals
• Used for shipping, offshore drilling, and aquaculture.
• Vulnerable to pollution and overfishing.
Continental slope :
The continental slope is the steeply sloping region of the seafloor that
extends from the edge of the continental shelf down to the deep ocean
floor
 Steep gradient: Much steeper than the shelf, often with slopes
ranging from 4° to 6°, but can be steeper in places.
 Depth range: Usually starts at about 200 meters depth and
extends down to around 3,000 to 4,000 meters.
 Boundary marker: Marks the true edge of the continent
geologically.
 Submarine canyons: Deep, V-shaped valleys often cut into the
slope, formed by turbidity currents or river erosion during past
sea-level changes.
3. Continental rise
The continental rise is a gently sloping area of the seafloor found between the continental
slope and the abyssal plain. It is formed by the accumulation of sediments.
Key Features:
 Gentle gradient: Slope is less steep than the continental slope—usually
less than 1°.
 Depth range: Typically lies between 3,000 to 5,000 meters below sea
level.
 Sediment deposits: Formed by sediments that slide down from the
continental slope through processes like turbidity currents, landslides,
and underwater avalanches.
 Transition zone: Connects the steep continental slope to the flat
abyssal plain

Importance:
• Acts as a depositional zone for sediments from land.
• Helps scientists understand past climate and geological history
through sediment analysis.
• Supports deep-sea ecosystems with fine sediments that
provide habitat for various organism
4. Abyssal plain
The abyssal plain is the flattest and most extensive part of the deep ocean
floor, lying between the continental rise and the mid-ocean ridges or oceanic
trenches.
Key Features:
 Flat and wide: Among the flattest areas on Earth, due to the thick
accumulation of fine sediments.
 Depth: Usually lies at 4,000 to 6,000 meters below sea level.
 Sediment cover: Composed of layers of fine sediments from land (via
turbidity currents) and biogenic particles (like shells and skeletons of
tiny marine organisms).
 Low relief: No significant slopes or features over large distances,
though seamounts, guyots, and small hills may appear
Importance:
• Covers about 50% of the Earth's surface.
• Plays a key role in carbon cycling and deep-sea
ecosystems.
• Home to unique marine life adapted to dark, high-
pressure environments.
• Important for studying earth’s geological and climate
history
 Sea mounts
 Definition: Underwater volcanic mountains that rise sharply from the ocean
floor but do not reach the surface.
 Origin: Formed by volcanic activity, usually at hotspots or mid-ocean ridges.
 Height: Can rise over 1,000 meters from the seafloor.
 Shape: Typically conical or rounded.
 Ecological role: Support diverse marine ecosystems, especially around their
summits

Guyots (also called Tablemounts)

• Definition: Flat-topped seamounts, usually eroded by wave action

when they were above sea level long ago.
• Formation: Start as volcanic islands or seamounts, eroded flat at
the top, then sink below sea level due to crustal movements.
• Feature: Flat summit and steep sides.
• Depth: Found deep below the ocean surface, often on abyssal
plains
Mid-oceanic ridges :
Mid-oceanic ridges are underwater mountain ranges formed by tectonic
plates pulling apart (divergent plate boundaries). They are the longest
continuous mountain systems on Earth.

Key Features:
 Formation: Created when magma rises from the mantle through
cracks in the ocean floor and solidifies as new crust.
 Location: Found in all major oceans. The most famous is the
Mid-Atlantic Ridge.
 Structure: Includes a central rift valley where the plates are
moving apart.
 Length: Over 65,000 km (40,000 miles) long globally.
 Activity: Frequent earthquakes and volcanic eruptions due to
tectonic activity.
Oceanic trenches
Ocean trenches are the deepest parts of the ocean floor, formed at convergent
plate boundaries where one tectonic plate is subducted (forced beneath) another
Key Features:
 Depth: Can be over 11,000 meters deep (e.g., Mariana Trench).
 Shape: Long, narrow, and V-shaped depressions.
 Formation: Occur where an oceanic plate is pushed beneath a continental or
another oceanic plate.
 Geological activity: Common sites for earthquakes, volcanic arcs, and
tsunamis.

Name Location Depth (approx.)

 11,034 meters
 Mariana Trench  Western Pacific Ocean
(deepest)
 Peru-Chile Trench (also  Off the west coast of
 ~8,000 m
called Atacama Trench) South America
 Java Trench  Indian Ocean  ~7,258 m
 Puerto Rico Trench  Atlantic Ocean  ~8,376 m
• Submarine Canyons
Deep valleys cut into the continental slope, often by ancient river erosion or
turbidity currents.
• Abyssal Hills
Small, rolling hills found on the abyssal plain; more common than seamounts
but less prominent.
• Hydrothermal Vents
Found near mid-ocean ridges, they release superheated water rich in
minerals, supporting unique ecosystems.
• Island Arcs
Curved chains of volcanic islands formed near ocean trenches (e.g., Japan,
Philippines).
• Fracture Zones
Long, linear cracks or faults on the ocean floor, offsetting mid-ocean ridges
due to plate movement
Tools to Study the Ocean Floor:
• Sonar (Sound Navigation and Ranging)
• Uses sound waves to map the depth and shape of the ocean floor.
• Echo sounding sends sound pulses and measures their return time.
• Satellite Altimetry
• Measures the height of the ocean surface from space.
• Detects underwater features by observing sea surface patterns caused by gravity.
• Submersibles
• Small, manned or unmanned vehicles that dive deep into the ocean.
• Used for exploration, photography, and collecting samples (e.g., Alvin).
• ROVs (Remotely Operated Vehicles)
• Unmanned underwater robots controlled from a ship.
• Equipped with cameras, sensors, and tools to study the seafloor.
• AUVs (Autonomous Underwater Vehicles)
• Self-guided underwater drones that map and scan the ocean floor.
• Used for long-term, deep-sea research missions.
• Drilling Ships
• Drill into the ocean floor to collect core samples for geological study.
• Example: JOIDES Resolution (part of ocean drilling programs).
• Seismic Reflection Devices
• Use vibrations to create images of the layers beneath the ocean floor.
• Helps in oil exploration and understanding Earth’s crust.
• Grab Samplers & Corers
• Tools used to collect sediment and rock samples from the seafloor.
 Importance of ocean floor profile
Importance of Ocean Floor Profile:
 Understanding Plate Tectonics & Earthquakes
 Reveals boundaries of tectonic plates (e.g., mid-ocean ridges, trenches).
 Helps predict earthquake and volcanic activity under the sea.
 Marine Navigation & Safety
 Knowledge of underwater topography is crucial for safe ship routes,
submarine operations, and laying undersea cables.
 Resource Exploration
 Identifies areas rich in oil, gas, and minerals (e.g., manganese nodules).
 Helps in planning deep-sea mining and drilling.
 Marine Ecosystems & Biodiversity
 Features like ridges and trenches support unique marine habitats.
 Helps in conservation planning and biodiversity protection.
 Climate & Ocean Circulation
 Ocean floor shapes influence ocean currents, which affect global climate.
 Cold and warm water flows are guided by the sea floor features.
 Tsunami Prediction
 Trench and slope analysis helps model and predict tsunami behavior after
undersea earthquakes.
 Scientific Research
 Provides insights into Earth’s history, evolution, and the processes shaping
the planet