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The Origins of the Ocean Unit (2B-2) – page 1
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The Origin of the Ocean Unit
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The Origin of the Idea of the “Big Bang” and the Origin of the Universe
A galaxy is a large groups of stars (millions or more) like the Sun and huge amounts gas and
“dust.” Their gravitational attraction for one another keep them together.
In 1929, the astronomer Edwin Hubble used the most powerful telescope in the world to measure
the distance to other galaxies and their speeds. He found that the galaxies are all flying apart and
that the farther apart they are, the faster they are moving. In other words, if you were to go back
in time, the galaxies would be closer to one another, and if you kept going back in time, you
would come to a moment in time about 14 billion years ago in which all the galaxies would be
“together.” (Technically it is galactic clusters – groups of galaxies – that are moving apart.
Within a group, some galaxies may be approaching one another.) These observations led to the
idea of the “Big Bang,” that our universe began in some kind of cosmic eruption about 14 billion
years ago. Since Hubble’s time, further observations – like those that confirmed Einstein’s
“General Theory of Relativity” and observations of the cosmic microwave background radiation
(the “echo” of the explosion) – have given additional support to the theory.
1. What is a galaxy?
2. Are galaxies moving away from one another or getting closer together?
3. Galaxies A and B are closer to one another than galaxies C and D.
Which pair of galaxies are moving away from one another faster, A & B or C & D?
4. About how old is the universe?
In other words, how much time has passed since “the Big Bang?”
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The Origin of Atoms and Stars
How can we tell what things far away in space are made of? Each kind of atom and molecule has
a unique “light fingerprint” called a spectra: each atom or molecule emits and absorbs very
specific “shades” of each color of light (and all other electromagnetic waves) depending upon its
temperature. In laboratories on Earth, scientists use this information to determine what things are
made of. Astronomers also use spectra to determine what stars, planets, and other objects in
space are made of.
Even though light is very fast, it takes time for light to travel. Therefore, when astronomers
look at very distant objects through their telescopes, they are also looking back in time.
When astronomers look as far into space as they can through our most powerful telescopes,
they are seeing that part of the universe “as it was” not long after the Big Bang.
As matter moving apart after the Big Bang cooled and “condensed” into atoms, the only
substances existed were hydrogen and helium, the two smallest atoms. To this day, most of the
atoms in the universe are made out of hydrogen and helium.
A water molecule (“H 2 O”) is made of 2 hydrogen atoms (“H”) and 1 oxygen atom (“O”) that
have joined together. Where did the oxygen necessary to make water come from?
All objects in the universe are attracted to all other objects (we call this force “gravity”), and
over time giant balls of hydrogen and helium gases collected together into stars like our Sun.
As new atoms fall into a star, they speed up, like a ball speeds up when you drop it. The resulting
collisions of vast numbers of atoms produce incredible temperatures and pressures inside the
star, eventually becoming large enough to “fuse” atoms together (two smaller atoms combine
into a larger atom). When atoms “fuse” together, a little bit of their mass is converted into other
forms of energy (e.g., heat, light) in accordance with the famous E = mc2, which powers the star,
making it shine. As the star burns hotter and hotter, the first atoms that are made in large
quantities include carbon, nitrogen, and oxygen, the building blocks of life. This is great for us
(we need those atoms for our bodies), but there is one problem: how do they get out of the star?
(Otherwise the atoms will not join together to form planets, people, etc.)
5. What are two most common kinds of atoms in the universe?
6. What force pulls together atoms to create stars?
7. Where are atoms larger than hydrogen and helium being made in the universe?
In other words, where are oxygen atoms being created?
8. What are large atoms made from? In other words, what is an oxygen atom created from?
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The Origin of Water
Eventually, a star runs out of its fuel: it is no longer hot enough to smash and fuse smaller atoms
together. At this point, the star begins to collapse (gravity pulls the atoms closer and closer
together). In large stars, the inward falling material collides and rebounds (like a “superball”)
outwards in a tremendous explosion called a supernova. The explosion scatters some of the
star’s atoms across space, creating huge “clouds” of gas and dust that we call nebulae.
In space, the atoms thrown out of the exploding stars cool down, and all but the lightest (like
hydrogen and helium) join together to from tiny bits of solid material. For example, oxygen
atoms and hydrogen atoms join to together to form molecules of H 2 0, better known as water.
Since the water is so cold, it is solid: ice. Many of the bits of dust in nebulae are tiny ice crystals
or tiny bits of rock and ice. In addition to water ice, spectra measured using telescopes show that
nebulae are made of a wide variety of atoms and molecules, including carbon monoxide,
ammonia, and even organic molecules!
In short, the “big bang” created hydrogen. Inside stars, hydrogen atoms combined to make
oxygen atoms. When the stars exploded, the hydrogen and oxygen were thrown out into space
where it was cold enough for them to join and form water molecules.
Thus, water is actually quite common in our universe. Telescope observations suggest that there
are at least 1 million Sun’s worth of water in our galaxy. Given that the Sun is a million times
more massive than the Earth, of which water is but a tiny part, this is a heck of a lot of water.
Even within our solar system, water is quite common. Water vapor is a (small) part of the
atmospheres of Mars and Venus, and ice covers large parts of the surface of Mars. Pluto is 3350% ice, one of the reasons that it was reclassified as a “dwarf planet.” Saturn’s rings are made
of ice (among other things), and ice covers moons and is a part of many asteroids (e.g., comets
are asteroids which are mainly ice.) Europa, one of Jupiter’s moons, is covered by ice. There are
fractures in the ice which suggests that the ice is shifting as it floats on top of something,
presumably a liquid water ocean! Enceladus, one of Saturn’s moons, is also covered by ice. A
huge geyser on its south pole sprays ice (and organic compounds!) high above the surface, so it
must have a source of liquid water below the surface!
9. What is a supernova?
10. What is a nebulae?
11. Is water common in the universe or rare? Is the Earth one of the few places with water?
12. In what form is most of the water in the universe: solid (ice), liquid, or gas (water vapor)?
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The Origin of the Earth
The solar system formed from a nebula as gravity pulled the atoms together. Over time, part of
the “cloud of dust and gas” became a whirling disc of material. Unlike when the first stars
formed after the Big Bang, this time there were larger, heavier atoms that could form solid
objects, not just the light atoms hydrogen and helium. When the star in the center (our Sun)
finally gained enough mass to “turn on,” its “solar wind” blew the lighter atoms to the outer
reaches of the solar system, leaving behind the heavier, rockier objects that joined to become
Mercury, Venus, the Earth, and Mars.
The Earth formed from countless collisions between these heavier, rocky objects, some small,
some large. As the “protoplanet” gained more material, it became more gravitationally attractive
and pulled in even more material. The collisions would have generated tremendous amounts of
the heat, so the early Earth would have been molten. Evidence of the collisions that produced the
Earth can be seen each night when you look up at the cratered surface of the Moon, which would
have formed in a similar manner. (Unlike the Earth, the Moon has no atmosphere to weather and
erode its surface, so its craters have not worn away.) Denser materials like iron tended to sink
towards the center (the “core”) of the Earth. As collisions became less frequent, the outer layer of
the Earth cooled by radiating heat into space and formed the solid outer “crust” of the planet. The
interior planet is still warm thanks to insulation provided by the crust and the decay of dense,
radioactive materials that sank towards the core in the beginning. This heat still leaks out at
volcanoes, and provides the energy that shifts the Earth’s crust during earthquakes.
“Radiometric Dating” can be used to determine when a rock that was magma or lava cooled down and
became a solid; in other words, the “age” of a rock is measured from when it first became a solid rock.
Radioactive atoms are “too big” and spontaneous break down into smaller atoms over time at a regular
rate called their “half life:” the time it takes for half of a group of larger, radioactive “mother” atoms to
break down or “decay” into smaller “daughter” atoms. By measuring the number of the bigger “mother”
and smaller “daughter” atoms in rock crystals, scientists can estimate the age of the rock: the more
“daughter” atoms there are relative to the number “mother” atoms, the older the rock is.
The oldest rock on the Earth is a little over 4 billion years old. (The oldest crystal, which would
have been part of an early rock and survived its destruction as a sediment, is about 4.3 billion
year old.) Moon rocks and meteorites are all about 4.4-4.6 billion years old. Thus, our best
estimate is that the solar system began to form perhaps as long as 5 billion years ago. By about
4.6 billion years ago, collisions were much less frequent, so rocks in space were no longer
getting altered, and by about 4 billion years ago (at the latest), the Earth’s surface was cool
enough to become solid rock. Very few of these rocks remain, because of 4-billion-years of
weathering and erosion.
13. What force pulled together the gas and dust of a nebula to form the Sun and the planets of
our solar system, including the Earth?
14. About how old is the Earth? In other words, roughly when did the Earth form?
The Origins of the Ocean Unit (2B-2) – page 5
The Origin of the Oceans
The Earth’s early atmosphere would have been very different from our mainly nitrogen and
oxygen atmosphere today. It would have primarily consisted of gases leaking out of volcanoes
(which would have covered the early Earth), primarily water and carbon dioxide – and some
nitrogen too – assuming that the volcanoes are like those we have today. Eventually, enough
water would have built up in the atmosphere for the very first (acid) rain. Over time, the rain
would fill the ocean basins. Comets probably contributed to filling the oceans as well. The heat
released by their impacts would have vaporized their water, but it would have rained down
sooner or later. The Earth may have lost its early ocean (and atmosphere) several times when
collisions with large objects blasted the water into space and beyond the Earth’s gravitational
reach. Eventually, though, collisions became less frequent and the oceans could steadily grow.
There is still some debate about whether comets or volcanoes are the primary source of the water
in the ocean. At the moment, observational evidence favors volcanoes. The comets that
astronomers have observed so far have too much “heavy water” (water in which one of the
hydrogen atoms has an extra neutron); in other words, if they were the source of the Earth’s
oceans, then our oceans should have more “heavy water” in them. However, the comets observed
so far have come from the outer solar system, and some scientists maintain hope that the comets
from the inner solar system might have the “right” amount of “heavy water.” Comets from the
inner solar system would have been much more likely to hit the early Earth and contribute to its
oceans than comets from the outer solar system. Inner solar system comets are very rare, and no
sufficiently-good observations have been made yet. The idea that comets from different parts of
the solar system might be different is not outlandish; after all, the planets in the inner and outer
solar system are quite different.
15. Describe the two major processes by which water filled up the ocean basins.
(a)
(b)
16. Which process probably supplied most of the water in the oceans?
The Origins of the Ocean Unit (2B-2) – page 6
The Origin of Salts in the Ocean
It would not have taken long for the first oceans to become salty. Water washed off the land
dissolved material (salts) from the land and carried it into the ocean. Warmed by the Sun, the
ocean water evaporated, leaving the salt behind in the ocean, and fell again on the land, carrying
more salt into the ocean. Ocean water also picks up chemicals at hydrothermal vents (places near
underwater volcanoes where chemicals leak into the ocean). Salts also are removed from ocean
water: chemicals are leached from the water near hydrothermal vents. In addition, many kinds of
ocean life absorb salts from the water. If their bodies sink to the bottom and become part of the
sediments on the bottom of the ocean, the salts remain in the sediments on the ocean floor. Rock
composed of seafloor sediments has a consistent amount of the salt chloride irrespective of its
age, suggesting that the salinity of the ocean has been pretty stable over most of the Earth’s
history (stable = a good thing for life in the ocean). Presumably, then, a balance between the
amount of salt entering and leaving the ocean was reached early on.
17. Where did most of the salt in the ocean come from?
18. Is the ocean getting saltier and saltier over time?
The Origins of the Ocean Unit (2B-2) – page 7
The Origin of Life
Fossils are the remains of once-living organisms: bones, impressions of skin or tracks, dung, etc.
The “fossil record” is basically all the fossils that have been found so far. The fossil record gives
us clues to what happened in the past on the Earth. However, it is an incomplete and imperfect
record of what happened that requires careful interpretation. For example, the hard parts of
organisms like bones and shells are much more likely to be preserved than softer parts like
tissues. Thus, we have a large number of fossils of shelled organisms like clams, but very few
fossils of jellyfish. This does not mean that shelled organisms were more abundant than jellyfish,
merely that they are more likely to be preserved.
Fossils are found in sedimentary rock, rock that forms from sediments (sand, mud) that pile up in
the bottom of valleys or the ocean floor. Different amounts and kinds of sediments pile up at
different times, each becoming its own layer. Layers on top are presumably “younger” in the
sense that they fell to the bottom later, after the ones below them, and the fossil organisms found
in each layer should have the same relative age as their layer. Scientists and amateur fossil
hunters have found that specific fossils are found in specific layers and no others. By identifying
the same kinds of organisms in layers from many parts of the world – and then looking at which
organisms are “above” or “below” them – scientists have pieced together a history of life on the
planet. (The order of the history – but not the exact times – was largely determined in the 19th
century just by studying layers of sedimentary rock.)
In the early 20th century, radiometric dating allowed scientists to more accurately determine the
time at which each layer formed. This work confirmed the sequence of events uncovered by the
earlier geologists and is shown above. Scientists have also compared the DNA of different
organisms and shown that it is consistent with the evolutionary history uncovered from the rocks.
First Appearance in the Rocks
Age of Rocks
winged insects, reptiles
≈ 300 million years ago
seed plants, amphibians
≈ 350 million years ago
1st LIFE ON LAND
≈ 440 million years ago
shelled organisms
≈ 540 million years ago
multicellular organisms
≈ 2.1 billion years ago
single-celled organisms
≈ 3.4 billion years ago
Notice the progression towards more complexity in the fossil record and how certain species
come before others. For example, seeded plants come after the first plants, and reptiles come
after amphibians (amphibians begin their life in the water, and then live on land). Some people
refer to this change and development of the life seen in the fossil record as the “fact of evolution”
(facts which must be explained) as opposed to the “theory of evolution” which explains why
The Origins of the Ocean Unit (2B-2) – page 8
these changes occurred. Using the theories of plate tectonics and biological evolution, scientists
recently found the remains of “tiktaalik,” an early tetrapod (the group of 4-limbed vertebrates
that made the transition to life on land), and thus filled in one more “gap” in the fossil record.
Ironically, several of its 4-limbed descendants (reptiles, mammals, birds) that evolved for life on
land would eventually return to the sea. Over the last few decades, some amazing discoveries of
early whale fossils have allowed scientists to piece together some of the story of how these
mammals slowly adapted to life in the ocean. You can actually see the nostrils moving up their
skulls, species by species, until it becomes the blowhole found on the top of modern whales and
dolphins.
The earliest life on the Earth were single-celled organisms (bacteria), and they were the only
kind of life on the planet for most of the Earth’s history. The earliest unequivocal fossils are the
remains of 3.4-billion-year-old stromatolites. Stromatolites are colonies of bacteria that grow in
shallow waters. Over time, sediments fall on top of them, and the bacteria migrate to the surface
where they can carry out photosynthesis to make their own food. The remains of the first land
plants and land animals appear only about 440 million years ago,
The early ocean was quite hospitable to early life compared to the land. Ocean water absorbs
sunlight, including harsh ultraviolet light. The ozone layer protects us from ultraviolet light
today, but ozone comes from oxygen, which would not have been present in large amounts in the
early atmosphere since it requires living organisms like plants and algae to make it in the first
place. In addition, the ocean is a more stable environment than the land. For example, the ocean
does not become as hot or as cold as the land. Ocean water also contains many substances
organisms need to survive, like nutrients. Moreover, life does not need to move around in search
of the things in the ocean, making the ocean hospitable to “simplest” life forms: water will carry
dissolved substances to them. Moving around can be advantageous, of course, but most of the
life in the ocean today is still small, drifting plankton, very similar to these early life forms.
(They still dominate the Earth.) Even viruses – tiny strands of DNA-like material that many say
are not even living things – can survive in ocean water without a cell wall to protect them from
the environment. Even after life moved onto land, its ocean origins are apparent in blood. In a
very real sense, we carry our own ocean of liquids inside us (optimized for us, of course).
19. Is the fossil record fairly complete, or are new discoveries filling in “gaps” all the time?
20. Where did life begin on the Earth, on land or in the ocean?
21. What were the earliest living things on the Earth? In other words, what kind of life is
found in the oldest fossil-bearing rocks?
22. Approximately how long ago did life begin on the Earth?
The Origins of the Ocean Unit (2B-2) – page 9
The Origin of the Atmosphere
The Earth’s early atmosphere would have been very different from our mainly nitrogen and
oxygen atmosphere today. It would have primarily consisted of gases leaking out of volcanoes
(which would have covered the early Earth), primarily water and carbon dioxide – and some
nitrogen too – assuming that the volcanoes are like those we have today.
At some point, early bacteria evolved a primitive form of photosynthesis, which became a
runaway success; these organisms could get more food than other organisms and prospered. In
addition, they transformed the world by adding vast amounts of their waste product – oxygen –
into the ocean. Initially, this oxygen would have bonded with dissolved materials in the oceans,
some of which became ocean sediments: at this point in the fossil record, we find huge, thick
layers of red (“rusted” iron) sedimentary rock around the world, a major source of the iron we
use today. Eventually, all the substances in ocean water that could have absorbed oxygen had
done so, and the waste-product oxygen began to build up in the ocean and the atmosphere. These
oxygen-producing bacteria radically altered the history of life on the Earth. Up until this time,
bacteria lived without oxygen. The new, oxygen-rich environment was toxic to most of them, so
they died off. Their descendants still survive in low-oxygen environments like the thick mud of
wetlands. (They produce the “stinky” smell.) Similarly, the photosynthesizing bacteria used up
the carbon-dioxide-rich atmosphere, and themselves had to evolve adaptations to lower carbon
dioxide levels and find some use for the now-abundant waste-gas oxygen. The oxygen
atmosphere eventually helped open up new living space: the land. Oxygen gas (O 2 ) can become
ozone (O 3 ), which protects land animals like us from ultraviolet radiation (if it is high in the
atmosphere).
23. Where did the gases in the Earth’s first atmosphere come from?
24. What were the two primary gases in the Earth’s first atmosphere?
25. What removed the carbon dioxide from the atmosphere and replaced it with oxygen?
How or why did they do so?
The Origins of the Ocean Unit (2B-2) – page 10
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