Chapter 1 Introduction to Planet “Earth”

Overview

The world ocean is the most prominent feature on Earth.
Oceans cover 70.8% of Earth’s surface.
The origin and development of life on Earth are connected to the ocean.
The oceans have a long history on Earth.

Earth’s Oceans

Earth has one ocean.

It is divided into four principle oceans and one other.

• Pacific Ocean
• Atlantic Ocean
• Indian Ocean
• Arctic Ocean
• Southern, or Antarctic, Ocean

Ocean Size and Depth

Pacific Ocean

• World’s largest ocean
  • Accounts for more than half of Earth’s ocean space
• World’s deepest ocean
• Earth’s largest geographic feature
• Named in 1520 by Ferdinand Magellan

Atlantic Ocean

• Half the size of the Pacific Ocean
• Shallower than the Pacific Ocean
• Separates the Old World from the New World

Indian Ocean

• Smaller than the Atlantic Ocean
• Similar depth as the Atlantic Ocean
• Primarily in the Southern Hemisphere

Arctic Ocean

• Seven percent the size of the Pacific Ocean
• Shallowest world ocean
• Permanent layer of sea ice a few meters thick

Southern Ocean or Antarctic Ocean

• Circumnavigates Antarctica
• Is really the parts of the Pacific, Atlantic, and Indian Oceans that lie south of 50° S latitude

The Seven Seas

• Smaller and shallower than oceans Salt water
• Usually enclosed by land
  • Sargasso Sea defined by surrounding ocean currents
• Directly connected to the ocean

Before the 15th century, Europeans considered the seven seas to be the following:

1. Red Sea
2. Mediterranean Sea
3. Persian Gulf
4. Black Sea
5.  Adriatic Sea
6. Caspian Sea
7. Indian Ocean

Comparing Oceans to Continents

• Average ocean depth is 3682 meters (12, 080 feet)
• Average continental elevation is 840 meters (2756 feet)
• Deepest ocean trench is the Mariana Trench at 11,022 meters (36,161 feet)
• Highest continental mountain is Mt. Everest at 8850 meters (29,035 feet)

Early Exploration of the Oceans

• Early “explorers” used boats to seek new fishing grounds for food.
• The ocean facilitated trade and interaction between cultures.

Pacific Navigators

• The peopling of the Pacific Islands required extensive travel in open boats and exceptional navigation skills.
• It was difficult because islands are widely scattered

Pacific People

• No written records exist of Pacific human history before the 16th century.
• Archeological evidence suggests island occupation by people from New Guinea as early as 4000–5000 B.C.
• Thor Heyerdahl sailed on a balsa raft – the Kon Tiki – to demonstrate migration of South Americans to Pacific Ocean islands.

European Navigators

• Phoenecians – first from Western Hemisphere to develop navigation arts
• Navigated circa 2000 B.C.
• Explored Mediterranean Sea, Red Sea, and Indian Ocean
• First circumnavigation of Africa
• Greek Pytheas
• Sailed northward using a simple method to determine latitude in 325 B.C.
• Navigated using the North Star
• Eratosthenes determined Earth’s

Europeans

• Herodotus produced inaccurate world map around 450 B.C.
• Claudius Ptolemy produced fairly accurate world map around 150 A.D.
  • Erroneously updated Eratosthenes’ original circumference estimation, later causing Christopher Columbus
• to believe he had reached Asia

The Middle Ages

• Arabs dominant navigators in the Mediterranean Sea
• Traded extensively with East Africa, India, and Southeast Asia
• Learned to use Indian Ocean monsoon winds for travel
• Vikings explored North Atlantic Ocean
  • Settled Iceland and Greenland in 9th and 10th centuries A.D.
  • Leif Eriksson designated part of eastern Canada Vinland (now Newfoundland) in 995 A.D.
  • Greenland, Vinland settlements abandoned by 1450 A.D. due to climatic cooling

Viking Routes and Colonies

The Age of Discovery in Europe 1492–1522

• Search for new Eastern trade routes by sea
  • Prince Henry the Navigator of Portugal sought trade routes around Africa.
  • Europeans explore North and South America.
    • Christopher Columbus was financed by the Spanish to find new trade routes to Asia.
    • Englishman John Cabot arrived in northeast North America in 1497.
• Spaniard Ferdinand Magellan circumnavigated the globe.
  • Was killed on a Pacific Island in 1521
• Juan Sebastian del Caño completed the circumnavigation in 1522.
• Voyages paved the way for the Spanish to take gold from the Incas and Mayas.
• Spain’s maritime dominance ended when England defeated the Spanish Armada in 1588.

Voyages of Columbus and Magellan

Voyaging for Science

• The English wanted to retain maritime superiority.
• Captain James Cook (1728–1779) undertook three scientific voyages.
  • Ships HMS Endeavour, Resolution,
  • Adventure
  • Mapped many islands in Pacific
  • Systematically measured ocean characteristics
  • Marine chronograph (longitude)

More high-technology tools available today

• Sonar
• Robotics
• Computers
• Satellites

Nature of Scientific Inquiry

• Natural phenomena governed by physical processes
• Physical processes similar today as in the past
• Scientists discover these processes and make predictions.
• Called the scientific method

The Scientific Method

Theories and Truth

• Science never reaches absolute truth.
• Truth is probable and based on available observations.
• New observations yield scientific progress. In reality, scientists have no formal method.

Formation of Earth and the Solar System

• Nebular hypothesis –
  • all bodies in the solar system formed from nebula
  • Nebula = cloud of gases and space dust
    • Mainly hydrogen and helium

Nebular Hypothesis

• Gravity concentrates material at center of cloud (Sun).
• Protoplanets form from smaller concentrations of matter (eddies).

Protoearth

• Larger than Earth today
• Homogeneous composition
• Bombarded by meteorites
  • Moon formed from collision with large asteroid
• Radioactive heat
  • Spontaneous disintegration of atoms
  • Fusion reactions
• Heat from contraction (protoplanet shrinks due to gravity)
• Protoearth partially melts
• Density stratification (layered Earth)

Density Stratification

• High density = heavy for its size
• Early Earth experienced gravitational separation.
  • High-density materials (iron and nickel) settled in core.
  • Less dense materials formed concentric spheres around core.

Earth’s Internal Structure

• Layers defined by
  • Chemical composition
  • Physical properties

Layers by Chemical Composition

• Crust
  • Low-density, mainly silicate minerals
• Mantle
  • Mainly iron (Fe) and magnesium (Mg) silicate minerals
• Core
  • High-density, mainly iron (Fe) and nickel (Ni)

Layers by Physical Properties

• Lithosphere
• Asthenosphere
• Mesosphere
• Outer core
• Inner core

Lithosphere

• Cool, rigid shell
• Includes crust and upper mantle
• About 100 km
• (60 miles) thick

Continental vs. Oceanic Crust

Asthenosphere

• Relatively hot, plastic
• Flows with high viscosity
  • Important for movement of lithospheric plates
• Base of lithosphere to about 700 km (430 miles) deep.

Isostatic Adjustment

• Vertical movement of Earth’s crust
• Buoyancy of lithosphere on asthenosphere –
  • Less dense continental crust floats higher than denser oceanic crust.
• Isostatic rebound – rising of crust formerly weighed down by glacier ice

Origin of Earth’s Atmosphere

• Outgassing – occurred during density stratification
  • Water vapor
  • Carbon dioxide
  • Hydrogen
  • Other gases
• Earth’s early atmosphere different from today

Origin of Earth’s Oceans

• Outgassed water vapor fell as rain.
• The first permanent oceans formed 4 billion years ago.
• Salinity developed from dissolved rock elements.
  • Early acidic rain dissolved more crustal minerals than today.

Life’s Possible Ocean Origins

• Earth’s earliest known life forms are 3.5-billion-year-old bacteria fossilized in ocean rocks.
• These are the building blocks for life on early Earth.
• There is no direct evidence of early Earth’s environment.

Oxygen

• Humans require O₂.
• Ozone (O₃) protects from ultraviolet radiation.
• Early Earth had little free oxygen.
• The lack of ozone may have helped originate life.

Stanley Miller’s Experiment

Organic molecules formed by ultraviolet light, electrical spark (lightning), and a mixture of water, carbon dioxide, hydrogen, methane, and ammonia.

Evolution and Natural Selection

• Organisms adapt and change through time.
• Advantageous traits are naturally selected. Traits are passed to the next generation.
• Organisms adapt to environments.
• Organisms can modify environments.

Plants and Animals Evolve

• Heterotrophs
  • Very earliest life
  • Require external food supply
• Autotrophs
  • Evolved later
  • Manufacture own food supply

First Autotrophs

• Probably similar to modern anaerobic bacteria
  • Survive without oxygen
• Chemosynthesis from chemicals at deep hydrothermal vents
• Supports idea of life’s origins on deep ocean floor in absence of light

Photosynthesis and Respiration

• Complex autotrophs developed chlorophyll.
• This allowed the use of the Sun for photosynthesis.
• Cellular respiration

Great Oxidation Event

• 2.45 billion years ago
• Increased oxygen and ozone eliminated the anaerobe food supply.
• Light and oxygen kill anaerobes. Cyanobacteria adapted and thrived.

Changes to Earth’s Atmosphere

• Photosynthetic organisms are responsible for life as we know it today.
• Reduce CO₂, increase O₂ to 21%
• High oxygen = biodiversity increase
• Low oxygen associated with extinction events

Plants and Earth’s Environment

Age of Earth

• Radiometric age dating
  • Spontaneous change/decay
  • Half-life
• Earth is about 4.6 billion years old.

Radioactive Decay

Geologic Time Scale

NOTE-The content provided, which aligns with Essentials of Oceanography by Alan P. Trujillo and Harold V. Thurman (11th edition)