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Exploring the Oceans. Chapter 16. Chapter 13. Section 1 Earth’s Oceans. How Did the Oceans Form?. About 4.5 billion years ago, there were no oceans. Sometime before 4 billion years ago, water vapor in the atmosphere condensed and fell as rain.

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Chapter 13

Section1 Earth’s Oceans

how did the oceans form
How Did the Oceans Form?
  • About 4.5 billion years ago, there were no oceans.
  • Sometime before 4 billion years ago, water vapor in the atmosphere condensed and fell as rain.
  • The rain filled the deeper levels of Earth’s surface and the first oceans began to form.
exploring the ocean floor
Exploring the Ocean Floor
  • Until recently, the ocean floor was unexplored.
  • The darkness, cold, and extreme pressure required new technology.
  • Most scientists prior to the 1900’s thought the ocean floor was flat, covered with layers of sediments washed in from the land.
hms challenger
HMS Challenger
  • First dedicated exploration of the oceans (1872).
  • Used a weighted line to find the depth of the water as they sailed.
  • Slow and inaccurate, but it gave scientists an idea of the ocean floor.
  • A bathymetric map is a topographic map of the ocean floor.
  • Each contour line on a bathymetric map is called an isobath.
  • Sound Navigation and Ranging.
  • Invented in WWI to hunt submarines.
  • Sound is bounced off the ocean floor to find the depth.
  • The closer the bottom is, to quicker the echo returns.
studying the ocean floor
Studying the Ocean Floor
  • Seeing by SonarScientists use sonar to determine the ocean’s depth.
  • Oceanography via Satellite Scientists use images from the satellite Seasat to study ocean currents.
revealing the ocean floor
Revealing the Ocean Floor
  • Regions of the Ocean FloorThe two regions of the ocean floor are the continental margin and the deep-ocean basin.
  • Underwater Real EstateThe continental margin and the deep-ocean basin are subdivided into different areas and have different features.
continental shelf
Continental Shelf
  • Gently sloping, shallow part of ocean floor that extends outward from the continent.
  • Varies from a few kilometers to over 1300-km from shore.
  • Provides nutrient rich home to large numbers of fish.
continental slope
Continental Slope
  • Steeply slanting portion after the shelf.
  • Bottom marks the edge of the continental crust.
  • Rapid moving currents carry large amounts of sediments.
  • Similar to landslides on land.
  • Often cut canyons in the continental slope.
continental rise
Continental Rise
  • Gentle slope at base of continental slope formed by accumulation of sediments that wash down.
abyssal plains

Mid-ocean ridge

Abyssal Plains
  • Smooth parts of the deep ocean floor.
  • Covered with fine grained muddy sediments (silt).
  • Cover large areas of the ocean floor.
  • Deep ocean sediments contain the remains of microscopic organisms.
  • After the organisms die, they sink to the ocean floor, forming a sediment called ooze.


mid ocean ridge
Mid-ocean Ridge
  • Divergent boundary underwater, where new crust is being formed from magma deep in the mantle.
  • Form underwater mountain ranges that seldom break the surface.
  • Can be 1000’s of km wide, and over 80,000-km long.
  • Passes through all the Earth’s oceans.
  • Volcanic mountains rising more than 1,000 m above the ocean floor.
  • Form near volcanic “hotspots”
volcanic island
Volcanic Island
  • These once underwater volcanoes grow so large they break the surface of the ocean.
deep sea trenches
Deep SeaTrenches
  • Deepest part of the ocean.
  • Many kilometers deeper than the surrounding abyssal plain.
  • The Marianas Trench is more than 11 km deep and 70 km wide.
characteristics of ocean water
Characteristics of Ocean Water
  • Dissolved Gases Nitrogen, oxygen, and carbon dioxide are the main gases dissolved in ocean water.
  • SolidsSodium chloride, or table salt, is the most abundant dissolved solid in the ocean. Other solids are also found in ocean water.
  • Ocean water is 3.5% salt.
ocean salinity
Ocean Salinity

Salinity varies in different parts of the ocean because of variations in evaporation, circulation, and freshwater inflow.

characteristics of ocean water continued
Characteristics of Ocean Water, continued
  • Temperature ZonesThe temperature of ocean water decreases as depth increases.
  • Zones based on the amount of temperature change.
  • Thermocline shows rapid temperature change.
oceans and sunlight
Oceans and Sunlight
  • Sunlight will barely reach 150-m deep into the ocean.
  • Below this it is always dark as night.
  • Since plankton need sunlight, most sea life will be in this first 150 meters.
features cont
Features (Cont.)
  • Reefs: coral reefs form in shallow water on continental shelves or along shorelines of volcanic islands
  • Atolls: if a volcanic island sinks below the surface of the water, the ring of coral reef left behind is called an atoll.
life zones in the ocean
Life Zones in the Ocean
  • Littoral Zone: shallow zone between high and low tide area. Organisms include crabs, clams, mussels, and algae.
  • Neritic Zone: Zone between low tide line to edge of continental shelf, no more than 200m deep. Gets plenty of sunlight to support plant organisms and animals such as coral, fish, squid, seals, whales, lobsters, and shrimp .
  • Oceanic Zone: Deep ocean zone
life zones cont
Life Zones (Cont.)
  • Estuaries: Bay or inlet where fresh river water mixes with ocean water. Low salinity.
  • Tidal Wetlands: low lying areas around estuaries periodically covered by ocean water. (Mangrove swamps and salt marshes)
ocean organisms
Ocean Organisms
  • Plankton: microscopic organisms that float near the surface. Phytoplankton are plant-like; zooplankton are animal-like.
  • Benthos: Organisms that live on the ocean floor (crabs, sea stars, seaweed).
  • Nekton: Organisms that swim (fish, dolphins, squid).
ocean resources
Ocean Resources
  • Fisheries: 75 million metric tons of food is taken from the ocean.
  • Minerals:
    • Salt dissolved in the water
    • Rocklike deposits known as manganese nodules are found on the ocean floor and include manganese, iron, copper, and nickel.
  • Oil: Large deposits of oil and natural gas occur beneath the continental shelves
Dead ocean organisms create sediment on the ocean floor called “ooze”.
  • The skeletons of diatoms (single-celled plantlike organisms) form deposits called diatomites that are mined for use in toothpaste, paint, and other chemical products.