Chapter 1Origins

OceanographyOceanographyAn Invitation to Marine Science, 7thAn Invitation to Marine Science, 7th

Tom GarrisonTom Garrison

Chapter 1 Study Plan

• Earth is an Ocean World

• Marine Scientists Use the Logic of Science to Study the Ocean

• Stars and Seas

• Earth, Ocean, and Atmosphere Accumulated in Layers Sorted by Density

• Life Probably Originated in the Ocean

• What Will Be the Future of Earth?

• Are There Other Ocean Worlds?

Chapter 1 Main Concepts

• Science is a systematic process of asking questions about the observable world by gathering and then studying information. Science interprets raw information by constructing a general explanation with which the information is compatible. Explanations (theories) may change as our knowledge and powers of observation change; thus, all scientific understanding is tentative.

• The universe’s observable mass consists mostly of hydrogen atoms. The heavy elements we see around us were constructed in stars. Our solar system is the result of the accumulation of elements formed in stars and distributed into space by cataclysmic events at the end of their lives.

• Earth is density stratified – that is, as Earth formed, gravity pulled the heaviest materials (iron, nickel) to its center as lighter minerals rose to the surface. Earth’s first solid surface formed about 4.6 billion years ago.

• Though most of Earth’s water was present in the solar nebula during the accretion phase, a barrage of icy comets or asteroids from the outer reaches of the solar system colliding with Earth may also have contributed a portion of the ocean-to-be.

• Life probably originated in the ocean.• Water, even liquid water, appears to be present in a few other places in

our solar system.

Earth Is an Ocean World

Beneath a very thin atmosphere, most of Earth’s surface is covered by a liquid-water ocean averaging 3,796 meters (12,451 feet) deep.

Earth Is an Ocean World

Sunrise on an ocean world. A liquid-water ocean moderates temperature and dramatically influences weather, nurtures life, and provides crucial natural resources.

Earth Is an Ocean World

The relative amount of water in various locations on or near Earth’s surface. More than 97% of the water lies in the ocean.

Earth Is an Ocean World

Average ocean depth is 4 ½ times as great as average land elevation.

Fig. 1-2, p. 5

Mid-Atlantic Ridge

Ocean’s deepest spot

Earth’s highest mountain

Pacific Ocean Basin, Earth’s largest feature

Stepped Art

Marine Scientists Use the Logic of Science to Study the Ocean

Marine Science (or oceanography) integrates many different types of science:

• Marine geologists study Earth’s crust and composition.• Physical oceanographers study of waves, currents, and

climate prediction.• Chemical Oceanographers study the ocean’s dissolved

gases and solids in the ocean.• Climate Specialists investigate the ocean’s role in Earth’s

changing climate.• Marine biologists study the nature and distribution of marine

organisms.• Marine engineers design and construct structures used in or

on the ocean.

Marine Scientists Use the Logic of Science to Study the Ocean

Oceanographers deploy a mooring containing temperature probes from the deck of R/V Oceanus during a gale off Cape Hatteras.

• Science is a systematic process of asking questions about the observable world by gathering and studying information (data)

• Science interprets raw information by constructing a general explanation with which the information is compatible.

• Scientists start with a question based upon something observed or measured.

• Working hypothesis – tentative explanation for the observation or measurement that can be tested and verified by further observations and controlled experiments

Marine Scientists Use the Logic of Science to Study the Ocean

• An experiment is a test that simplifies observation in nature or in the laboratory by manipulating or controlling the conditions under which the observations are made.

• Theory – a hypothesis consistently supported by observation or experiment.

• Laws – larger constructs that summarize experimental observations.

• A law summarizes observations while a theory provides an explanation for the observations.

Marine Scientists Use the Logic of Science to Study the Ocean

The Scientific Method

An outline of the scientific method, a systematic process of asking questions about the observable world and then testing the answers to those questions.

Fig. 1-4, p. 7

Curiosity

A question arises about an event or situation: Why and how does this happen? Why are things this way?

Stepped Art

TheoryPatterns emerge. If one or more of the relationships hold, the hypothesis becomes a theory, an explanation for the observations that is accepted by most researchers.

ExperimentsTests are undertaken in nature or in the laboratory. These tests permit manipulating and controlling the conditions under which observations are made.

HypothesisA tentative explanation is proposed. Controlled experiments are planned to prove or disprove potential cause-and-effect relationships. A good hypothesis can predict future occurrences under similar circumstances.

Observations, measurements

Our senses are brought to bear: What is happening? Under what circumstances? When? How does it operate? Does there appear to be a dependable cause-and-effect relationship at work?

Law

Theories can evolve into larger constructs: laws. Laws explain events in nature that occur with unvarying uni-formity under identical conditions. Laws summarize experimental observations.

Stars and Seas

• To understand the ocean, we need to understand how it formed and evolved through time.

• Because the world ocean is the largest feature of Earth’s surface, scientists believe the origin of the ocean is linked to Earth’s origin.

• The origin of Earth is linked to that of the solar system and the galaxies.

Earth Was Formed of Material Made in Stars

• The universe apparently had a beginning called the big bang that occurred ~13.7 billion years ago.

• All of the mass and energy of the universe was concentrated at a geometric point at the beginning of space and time, the moment when the expansion of the universe began.

• We don’t know what initiated the expansion, but it continues today and will probably continue for billions of years, perhaps forever.

Stars and Planets are Contained within Galaxies

Our Milky Way Galaxy pictured from afar. We’re inside and dust obscures our view, but this painting is a good guess about what our galaxy looks like, based on many different types of observations. Our solar system is a little more than half-way out from the center in one of the blue spiral arms.

Stars and Planets Are Contained within Galaxies

• What do stars have to do with the ocean?

• Most of the substance of Earth, its ocean, and all living things, was formed by stars.

• Every chemical element heavier than hydrogen was manufactured and released into space by stars.

• Our sun, like all normal stars, is powered by nuclear fusion.

Stars and Planets Are Contained within Galaxies

A filament of hot gas erupts from the face of our sun. Like all normal stars, the sun is powered by nuclear fusion – the welding together of small atoms to make larger ones. The entire Earth could easily fit into this filament’s outstretched arms.

Stars Make Heavy Elements from Lighter Ones

The origin of a solar system in the spiral arm of a galaxy. Our sun and its family of planets were formed in this way about 5 billion years ago.

Solar Systems Form by Accretion

Planet-building in progress. Accretion of planets occurs when small particles clump into large masses.

Earth Accumulated in Layers Sorted by Density

• How did Earth become density stratified?

• Young Earth was probably homogeneous

• Heat and gravitational pressure caused Earth to partially melt

• Gravity then pulled the iron present into the center of Earth

• This heated Earth further and lighter minerals migrated to Earth’s surface and formed the crust

(top) The planet grew by the aggregation of particles. Meteors and asteroids bombarded the surface, heating the new planet and adding to its growing mass. At the time, Earth was composed of a homogeneous mixture of materials.

(middle) Earth lost volume because of gravitational compression. High temperatures in the interior turned the inner Earth into a semisolid mass; dense iron (red drops) fell toward the center to form the core, while less dense silicates move outward. Friction generated by this movement heated Earth even more.

(bottom) The result of density stratification is evident in the formation of an inner and outer core, a mantle, and the crust.

Earth Accumulated in Layers Sorted by Density

• How did water and water vapor form on early Earth?

• The Sun stripped away Earth’s first atmosphere

• Gases, including water vapor, released by the process of out-gassing, replaced the first atmosphere.

• Water vapor in the atmosphere condensed into clouds.

• Eventually, the surface cooled enough for water to collect in basins.

Earth Accumulated in Layers Sorted by Density

Comets may have delivered some of Earth’s surface water. Intense bombardment of the early Earth by large bodies – comets and asteroids – probably lasted until about 3.8 billion years ago.

Earth Accumulated in Layers Sorted by Density

The early atmosphere was very different from the atmosphere today.

Earth Accumulated in Layers Sorted by Density

Life Probably Originated in the Ocean

Fossil of a bacteria-like organism (with an artist’s reconstruction) that photosynthesized and released oxygen into the atmosphere.

Among the oldest fossils ever discovered, this microscopic filament from northwestern Australia is about 3.5 billion years old.

What Will Be the Future of Earth?

• How long can Earth exist?

• Our Sun will begin to die in 5 billion years.

• 6 billion years from now the sun will enter the red giant phase and will engulf the inner planets.

• At that time, Earth will probably be recycled into component atoms.

• See Figure 1.8 for a timeline of Earth.

What Will Be the Future of Earth?

Are There Other Ocean Worlds?

• Where have scientists found evidence of water?

• Europa– The gravitational pull of Jupiter twists Europa,

cracking the ice crust and warming the interior.– In some areas the ice has broken into large

pieces that have shifted away from one another but fit together like a jigsaw puzzle.

– This suggests the ice crust is lubricated by slush or water. A global ocean greater in volume than Earth’s ocean may lie beneath the movable crust. It may also be salty - salinity has been detected by Galileo’s magnetometers.

In 2005, Europe’s Mars Express orbiter imaged a glacier in an unnamed crater in the vast plains of northern Mars. This 200 meter (656 foot) thick remnant of a larger ice sheet is shielded by the frosty shade of the crater walls.

Are There Other Ocean Worlds?

Are There Other Ocean Worlds?

• Where have scientists found evidence of water?

• Titan – Saturn’s largest moon, may have an ocean of hydrocarbons.

• Mars– Early in its history, Mars may have had a thick

atmosphere of carbon-dioxide, much like the atmosphere of the early Earth.

– An ocean may have existed on Mars about 3.2 billion years ago.

– Over the eons, rocks on the Martian surface absorbed the carbon dioxide and the atmosphere grew thin and cold and the ocean disappeared

Chapter 1 in Perspective

In this chapter you learned that Earth is a water planet, possibly one of few in the galaxy. An ocean covering 71% of its surface has greatly influenced its rocky crust and atmosphere. The ocean dominates Earth, and the average depth of the ocean is about 4½ times the average height of the continents above sea level. Life on Earth almost certainly evolved in the ocean; the cells of all life forms are still bathed in salty fluids.

We study our planet using the scientific method, a systematic process of asking and answering questions about the natural world. Marine science applies the scientific method to the ocean and the living organisms dependent on the ocean.

Most of the atoms that make up Earth and its inhabitants were formed within stars. Stars form in the dusty spiral arms of galaxies and spend their lives changing hydrogen and helium to heavier elements. As they die, some stars eject these elements into space by cataclysmic explosions. The sun and the planets, including Earth, probably condensed from a cloud of dust and gas enriched by the recycled remnants of exploded stars. Earth formed by the accretion of cold particles about 4.6 billion years ago. Heat from debris and radioactive decay partially melted the planet, and density stratification occurred as heavy materials sank to its center and lighter materials migrated toward the surface. The ocean formed later, as water vapor trapped in Earth’s outer layers escaped to the surface through volcanic activity during the planet’s youth. Life originated in the ocean very soon after its formation. We know of no other planet with a similar ocean, but water is abundant in interstellar clouds and other water planets are not impossible to imagine.

In the next chapter you will learn that science and exploration have gone hand in hand. Voyaging for necessity evolved into voyaging for scientific and geographical discovery. The transition to scientific oceanography was complete when the Challenger Report was completed in 1895. The rise of the great oceanographic institution quickly followed, and those institutions and their funding agencies today mark our path into the future.