Take-away Topics

Following are examples of coastal erosion by waves:

The example below is that of a delta:

Deltas are of three types:
(a) river-dominated (e.g., Mississippi, Danube, Po); (b) wave-dominated (e.g., Nile, Niger, São Francisco); and (c) tide-dominated (e.g., Colorado, Ganges-Brahmaputra, Mekong).

	to Poorna Pal's Pages at the Glendale Community College
Ocean 115: Physical Oceanography
This 3-unit physical science lecture course examines the physical, chemical and geological aspects of oceans and the oceanic environment. The companion laboratory course is: Ocean-116 (Laboratory Exercises in Physical Oceanography). Also try Biol-125 (Marine Biology) and Biol-126 (Marine Biology Lab.) in order to round up your Marine Sciences learning at the Glendale College. For students taking Ocean-115 and Ocean-116 to complete their Physical Science GE requirements, it may be a good idea to satisfy their GE requirement in Life Sciences by taking Biol-132 (Introduction to Marine Sciences).		Updated on 05.05.2015

Home | My Book | Physical Geol: Geol-101, Geol-111 | Environmental Geol: Geol-102, Geol-112 | Oceanography: Ocean-115, Ocean-116

Talking Points

Earth's Oceans
Why Venus and Mars Lack Water?
Physiography and the formation of the seafloor
Plate Tectonics
Sediments
Seawater chemistry
Ocean physics
Atmospheric circulation
Ocean circulation
Waves, Tides and Tsunamis
Coasts and the coastal processes

Earth's oceans

This "Blue" and "Lonely" 3rd Rock from the Sun:

Earth is called the "Blue Planet" because oceans, the huge water-filled basins, cover most (~71%) of the Earth's surface and as yet seem unique to the Earth.

It is not that the chemicals that make water (H₂O) occur only on the Earth, indeed universe has abundant supplies of hydrogen and oxygen. Nor it is that the temperatures between 0°C and 100°C, i.e., the freezing and boiling points of water, respectively, are found only on the Earth.

It is not that water is colored blue, nor it is that oceans reflect the "blue" sky. The reason, simply, is that the farther the light (the visible part of the spectrum) travels the more blue it appears ― a clear sky therefore appears blue, as does still water. Where do you think that blue goes, otherwise, when the water turns choppy?

Earth is also called the "Lonely Planet" because, to the extent we are as yet aware, life remains unique to the Earth.

Earth is also called the "3rd Rock from the Sun". Earth is the third planet from Sun, the center of the solar system, Mercury being the first, Venus the second, and Mars the fourth. All these planets, including the Earth, are called terrestrial or Earth-like, and rock because they contain silica (SiO₂). Jupiter and Saturn are compositionally similar to Sun, and mostly contain hydrogen (H) and helium (He), whereas Uranus and Neptune have dominantly C (carbon), N (nitrogen) and O (oxygen) in composition.

Why seasons?

Earth's spin axis tilts 23.5° from the vertical. Thus, as Earth completes is orbit, North pole tilts towards the Sun one-half the time, with peak at the Summer Solstice, whereas South pole tilts towards the Sun during the other half, with peak at Winter Solstice. Tropics, bounded by Tropic of Cancer (23.5°N) and Tropic of Capricorn (23.5°S), receive Sun all year round and therefore have no seasons, whereas temperate latitudes have seasons. Also, the northern temperate region (23.5°N to 66.5°N or the Arctic Circle) has summer when the southern temperate region (23.5°S to 66.5°S or the Antarctic Circle) has winter, and vice versa. What if Earth's spin axis became nearly vertical, as is the case with Venus? Will we still have the seasons?

Some Characteristics of Earth's Oceans:

	Oceans (area = 361 million km²) cover ~71% of the Earth's surface.
	Three oceans account for most of the water on Earth: Pacific is the largest (with about one-half of the oceanic surface area), followed by the Atlantic and Indian oceans.

Note how Pacific Ocean (above left) covers almost the entire view of the Earth. Indeed, in terms of the total surface area, Pacific is larger than the Atlantic (center) and Indian (right) oceans combined and covers almost one-half of the ocean surface area (or about a third of the Earth's surface).

See the world map at http://atlas.mapquest.com/atlas/?region=world

The distribution of land and oceans is hemispherically asymmetric, with most of the land in the northern hemisphere and most of the oceans in the southern hemisphere.

	Oceans have an average depth of about 4km. Almost 70% of the ocean-floor lies between the depths of 3-6 km, however. This is the abyssal sea floor.
	The ocean floor is typically made up of basalts. Since basalt is essentially a volcanic rock, this suggests that volcanism has created the ocean floor.
	Oceans have existed throughout the Earth history. Marble forms from limestones, for instance, and limestones only form in the oceans. The existence of 2.5-3 Ga old Larkana marble (the marble that the famous Taj Mahal is made up of) thus suggests that oceans existed pretty early in the Earth's ~4.5 Ga history.

How deep is the world ocean, really?

In 1856, Alexander Bache, a great-grandson of Benjamin Franklin, was perhaps the first to use tsunami wave-velocity equation to estimate the average ocean depths. This equation is

V = √(gxD)

where V is the shallow water wave velocity in meters per second, g = 9.81 m/sec² is gravitational acceleration on Earth, and D is the basin-depth in meters.

Noting that the average tsunami velocity is about 200 m/sec, all that Bache had to do was to rewrite this equation as D = V²/g so that, plugging into its right-hand side the values of V = 200 m/sec and g = 9.81 m/sec, he obtained the value D ≈ 4000 m or 4 km, a value surprisingly close to our modern estimate!

*Tsunamis generated by the April 1946 Aleutian trench, Alaska, temblor took 4.6 hours to reach Honolulu, Hawaii, a distance of about 3500 km, for instance. The map alongside shows the estimated Pacific Ocean tsunami travel times from or to Hawaii.

This map shows how many hours it would take for a tsunami generated anywhere on the rim of the Pacific basin to reach Hawaii. The dots indicate the locations of earthquakes that have generated tsunamis which have affected Hawaii.

The distribution of land and oceans has changed oftentimes in the geological past:

One of the Himalayan peaks, Mt. Annapoorna (shown on the left), is made up of limestones with ~200 Ma old ammonite fossils, for instance, suggesting that an ocean once existed where we now have the world's tallest mountains!

Look, for that matter, at the ~300 Ma old coral limestones occur in Utah and Maine, and both these regions are not only way inland but also at high latitudes whereas coral reefs always occur in the Tropics. Clearly, these locations were located in the tropics when these coral limestones formed.

The presence of ~250 Ma old Kaibab limestones in the Grand Canyon suggests that an ocean existed at this location ~250 Ma ago.

Consider, likewise, the example of ~250 Ma old Kaibab limestones that form the floor of the Kaibab National Park where the Grand Canyon is located.

The "Hydrological Cycle":

Hydrological cycle is the continuous recycling of water on Earth, by way of

Evaporation (E) ® Precipitation (P) ® Run-off (R)

except that run-off plays opposite roles in the land versus the oceans.

Oceans have 80-97% of the water on Earth but cover ~71% of the Earth's surface, after all. Evaporation mostly occurs on the oceans therefore, whereas precipitation, or the return of this lost water from the atmosphere, occurs evenly on the oceans and the land.

=How much water do the oceans have?

=Hydrological cycle by the numbers

The oceans clearly lose more water by evaporation than what precipitation can bring back. In the case of land, on the other hand, precipitation brings back more water than what is lost by evaporation.

NASA | Earth Science Week:

Water, Water Everywhere!

6:32

http://www.youtube.com/watch?v=qyb4qz19hEk&feature=related

It is this deficit in the oceans, and the excess on land, that is balanced by run-off from land to the oceans. We should therefore look at the balancing of water in the oceans as E = P+R whereas this balancing occurs on land as E+R = P!
This enables us to write the correct equation for the hydrological cycle as
Evaporation (E) = Precipitation (P) + Storage

How long does run-off need to fill the ocean basins?

Run-off brings about 15 billion tons of sediments to the world ocean every year (for the average sediment density of 2300 kg/m³, say, this amounts to about 7 billion m³ per year.

Now, with the total volume of the world ocean as 1.37 x 10⁹ km³ (= 1.37 x 10¹⁸ m³), this means that the time needed for run-off to fill the ocean basins is

1.37 x 10¹⁸ m³	=	about 200 million years
7 x 10⁹ m³ per year

Atmosphere's role:

Note here that atmosphere collected just as much water through evaporation as it gave back by precipitation. But why would water vapor that goes to the atmosphere precipitate back? This is because temperatures in the atmosphere decrease with height, up to a height of ~11 km from Earth's surface (or in the Troposphere), so that the moisture-laden warm air than rises (i.e., evaporation) must return when it cools down (i.e., precipitation). What if this thermal profile of the atmosphere changes?

Suppose the tropospheric temperatures are the same throughout, no matter what the height above the Earth's surface? Wouldn't that make for a foggy Earth?

Run-off matters:

Now, run-off not only carries excess water (= precipitation ― evaporation) from land to the oceans but also erodes land features and dumps them in the oceans. In course of time therefore, say in a matter of 200-250 Ma, hydrological cycle is bound to flatten the land surface and fill-up the ocean basins, so leaving the Earth's surface smooth, flat and featureless. That would only accelerate evaporation, and destroy the cycle itself.

How do we know that the hydrological cycle has a 200-250 Ma life-span?

Run-off deposits ~15 billion tons of sediments into the ocean every year.
This amounts to 15 trillion kg/yr = 7.5 billion m³/yr (assuming average sediment density of 2 g/cm³ = 2000 kg/m³).
Total volume of the world ocean is 1.37 billion km³ = 1.37x10¹⁸ m³.
Therefore, the time needed for run-off from land to fill the ocean basins is
= 1.37x10¹⁸ m³ ÷ 7.5x10⁹ m³/yr = 1.83x10⁵ years
= 183 Ma

Plate tectonics:

This is precisely where plate tectonics come in. It compliments hydrological cycle's
flattening of the Earth surface by creating new seafloor and mountain belts.

Plate tectonics is the unifying theme in earth sciences that combines the earlier postulates of (a) continental drift, (b) seafloor-spread and (c) mountain building. Here,

continental drift is the idea that continents change their positions over time, e.g.,
Wegner's Pangea, a supercontinent that comprised all the present-day continents into a
single assembly and existed about 250 Ma ago;

seafloor-spread is the idea that seafloor forms by repeated volcanic eruptions at the rift
valley that drives the earlier adjacent landmasses farther and farther apart, e.g., the Atlantic
Ocean formed by volcanism at the Mid-Atlantic Ridge that drove the Americas to the west
and Europe and Africa to the east, so creating the Atlantic Ocean; and

mountain building is the idea that a folded mountain belt like the Himalayas formed when
India, then an island adjacent to Africa, drifted northwards and collided against the
Eurasian landmass.

Thus, as hydrological cycle smoothens the Earth surface by leveling the land and filling up the
ocean basins, plate tectonics creates new ocean basins and mountain belts. As for the Earth's
surface features, therefore, plate tectonics and hydrological cycle act as two competing processes.

Why Venus and Mars lack Water?

Earth, Venus and Mars:

Water, the H₂O molecule in liquid state (i.e., between the temperatures of 0°C and 100°C) should be quite common in our Solar System as well as elsewhere in the universe. It is not as if there exists any shortage of hydrogen and oxygen, after all.

Click here to access the Periodic Table of Elements.

Indeed, water is hardly common within our own Solar System itself. Not all of them are Earthlike, anyway. Density, defined as mass per unit volume, is a measure if their chemical compositions. Thus examined, the inner planets (Mercury, Venus, Earth and Mars) are compositionally alike

Note that the three neighboring planets ― Earth, Venus and Mars ― have similar densities and compositions. Also, compared to the vast distances in the Solar System, they are also quite close to one another and to Sun. Together with Mercury, they are called terrestrial (or Earth-like) planets. But, unlike the Earth, neither Venus nor Mars have much water. Venus is very hot, with surface temperatures of ~700K or 427°C. Mars is very dry so that, much like any arid region, the temperatures on Mars range from very cold to very hot.

Distance from the Sun is not the reason why Venus and Mars lack water, because the surfaces of all the three planets receive similar amounts of insolation (incoming Solar radiation). The reason lies in their dissimilar atmospheres and the lack of plate tectonism.

As for their atmospheres, note the following facts:

The atmospheres of Venus and Mars are carbon-rich, with ~90% CO₂. Earth's present-day
atmosphere is significantly different, and contains only ~0.035% C, but had about the same
CO₂ once upon a time as the venusian atmosphere today.

The densities of the three atmospheres are significantly different, however ― Venusian
atmosphere is ~90 times thicker than Earth's atmosphere whereas the latter is ~90 times
thicker than the Martian atmosphere!

As for plate tectonics, there is no evidence that either Venus or Mars ever experienced this activity.

Venus, the Hot Gal Next Door!

Venus is located at ~0.72 AU from Sun
(1 AU = mean Earth-Sun distance). As solar
radiation follows the inverse-square law, and
~1370 W/m² of solar heat reaches the Earth,
the amount of solar heat that reaches Venus
is ~2640 W/m²(= 1370 ¸ 0.72²).

Venus Express is European Space Agency's mission to Venus that reached that planet on 11 April 2006. Click on the image on the left to access the initial results of this probe published in a recent issue of the journal Nature.

Earth's atmosphere reflects ~32% of this insolation away, so letting only ~930 W/m² of this solar heat reach the surface. The thick venusian atmosphere reflects away ~76% of this insolation, and what reaches its surface is barely 630 W/m². Clearly, proximity to the Sun is not the reason why Venus is so hot. Rather, it should be colder than the Earth!

Why is Venus so hot then? Two reasons have contributed to it:

Venus is a slow and retrograde rotator. It completes one spin on its axis in 243 earth days, spinning in a direction opposite to the other planets (i.e., Sun rises in the west there, not in the east), and completes one orbit about the Sun in 223 earth days. One side of the planet thus faces Sun almost 80% of the time.

The thick venusian atmosphere then retains and evenly distributes the solar heat thus absorbed by the planet, so leaving the "day" and "night" sides of Venus almost equally hot.

Was the Earth just as hot as Venus once upon a time, then, when Earth's atmosphere was as rich in CO₂ as present venusian atmosphere? Probably not, when we note that much of the volcanism on Earth has been expended in creating the seafloor (i.e., associated with plate tectonism) whereas venusian volcanism is of the plume-type (i.e., the kind we find in Hawaii). The volatiles released by the former are more likely to stay in the lower atmosphere than go to the upper atmosphere whereas the opposite is likely to be true of those released by the latter.

Water on Mars!

Mars, the "Red" planet, is located on the far side
of the Earth from Sun, at a distance of ~1.5 AU from Sun. The amount of solar heat that reaches Mars is ~610 W/m² (= 1370 ¸ 1.5²), therefore. But the thin Martian atmosphere can hardly filter off any significant fraction of this heat. Clearly, incident solar radiation on the Martian surface is about the same as that on Venus.

Of all the planets, Mars's seasons are the most Earth-
like, due to the similar tilts of the two planets' rotational
axes. However, the lengths of the Martian seasons are
about twice those of Earth's, as Mars’ greater distance
from the sun leads to the Martian year being about two
Earth years in length. Martian surface temperatures vary
from lows of about −140°C during the polar winters to
highs of up to 20°C summers.The wide range in
temperatures is due to the thin atmosphere which
cannot store much solar heat, and low atmospheric
pressure.

The Northern Polar Icecap on Mars

Martian landscape

As for the hydrological cycle on Mars, there is good evidence that water was once abundant enough on Mars to have produced the landscape we now see but now remains confined to the subsoil and the polar ice cap. The question, then, is as to how and why might Mars have lost its hydrological cycle.

A good chance is that Mars is too small to have had a strong enough gravitational field that would have prevented water from escaping into the space. It is not that Martian atmosphere is not thick enough ― the total quantity of CO₂ in the Martian atmosphere greatly exceeds that in the Earth's atmosphere, after all. It is just that the planetary atmosphere must have some mechanism to prevent the escape of water into the outer space. Unfortunately, though, appealing to low density of Martian atmosphere to argue that its temperature gradient is too gentle to have prevented the escape of atmospheric moisture (unlike Earth’s tropospheric thermal gradient that is steep enough to have retained the hydrological cycle), ignores the fact that a vigorous hydrological cycle may have once existed on Mars.

There is also some evidence that plate tectonics once occurred on Mars, but no longer does. The question is whether the striped magnetic anomalies reported on Mars that seem so similar to those seen on Earth's oceans indeed provide the evidence of now defunct but once active Martian plate tectonics. Also, if indeed so, the question is whether these anomalies formed 4 Ga ago or about 1000 Ma ago. We could nonetheless claim that Mars lacks hydrological cycle because it no longer has the plate tectonics to create new ocean basins to replace the ones flattened by the “run-off” component of hydrological cycle.

The presence of hydrological cycle on the Earth, and its absence on Mars, is therefore due as much to the planetary atmospheres as to plate tectonics, much as the case is with Venus.

The seafloor

Physiography:

Click on this map below to browse the NASA map of world ocean floor

or click on this map on the right to access the World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.

Try this "Topography of the ocean floor" exercise at the URL: http://gyre.umeoce.maine.edu/physicalocean/Tomczak/IntExerc/basic2/quest02.html

A peculiarity of the heights and depths on Earth's surface is their bimodal distribution, seen in the hypsometric graph below.

Clearly, even if all the waters on the Earth disappear, whether as moisture in the atmospheric or in the polar icecaps, oceans would still show up as deep basins!

Overall, these basins (colored blue in the above hypsometric graph) can be grouped as (a) continental margins and (b) deep ocean basins. Of these:

continental margins (a) can be active (i.e., seismic or tectonic) or passive (i.e., aseismic);
(b) comprise ~14% of the oceanic area, with ~740 m average depth; and (c) carry ~52% of the world's sediments (thickness <7 km) that are mostly brought by run-off from land; and

deep ocean basins (a) cover ~85% of the ocean surface and (b) comprise (i) abyssal seafloor (~80% of ocean surface, ~4.5 km average depth, ~13% of world's sediments averaging ~200 m in thickness), (ii) ridges and rises (e.g., the Mid-Atlantic Ridge, East Pacific Rise etc., that cover ~6% of ocean surface, have ~2.5 km average depth, and carry ~7% of the world's sediments), and (iii) deep sea trenches and island arcs (~1% of ocean surface and ~6.5 km average depth).

The Geology of the Seafloor

Bathymetric, magnetic and stratigraphic profiles across the submarine ridges and rises tend to be symmetric, as can be seen from the example of Mid-Atlantic Ridge alongside.

The ridge axes also have high seismicity, high heat flow, and symmetric magnetic anomalies.

Shown below is a map of the ridges and rises worldwide, for instance. See how well their locations correlate with the world seismicity map. Get the world seismicity map by clicking on this image .

Marine magnetic anomalies have perhaps provided the most information on seafloor and how it has been created. Typical of the magnetic profiles obtained over mid-ocean ridges is the observation of alternate rises and falls. As the seafloor is basaltic, these marine magnetic stripes are the records of geomagnetic field's polarity reversals as the lavas extruded.
Click on this image alongside to learn
about how these anomalies are mapped
and what they actually mean in terms
of the seafloor's history of evolution.

This has enabled the detailed mapping of seafloor ages. Clicking on the map below will enable you to view and download the original digital map of ocean floor ages from the NGDC (National Geophysical Data Center).

The Seafloor Spread Model:

Note in the above map how the seafloor is youngest at the axis of the ridge and becomes progressively older the farther we get from the ridge axis. Thus, the oldest seafloor in the western north Pacific, and adjacent to the North American and African coasts of the Atlantic.

As shown in the animation from USGS alongside, this is simply because the basaltic seafloor forms by repeated volcanic injections at the ridge axis. Newer injections thus drive the older seafloor farther from the axis of the ridge.

The alternate blocks of 'normal' and 'reversed' magnetic polarities, creating the marine magnetic anomalies, form on this picture merely because of the geomagnetic polarity reversals during these intermittent volcanic injections. This animation alongside too is from the USGS and demonstrates how this occurs.

Sea-Floor Spreading and Subduction Model:

Read this USGS Open-File Report 99-132 (On-Line Edition) by John C. Lahr that describes how to build a model of the outer 300 km (180 miles) of the Earth that can be used to develop a better understanding of the principal features of plate tectonics, including sea-floor spreading, the pattern of magnetic stripes frozen into the sea floor, transform faulting, thrust faulting, subduction, and volcanism.

North Cascades Geology: Sea-Floor Spreading:

Try this USGS page to compare magnetic stripes on the sea floor to the magnetic reversals in basalt on the land as seen in a vertical cliff and explains how this supports the sea floor spread model.

Plate Tectonics

What is plate tectonics all about?

The postulate of global plate tectonics

unifies the earlier hypotheses of continental drift, sea-floor spread and mountain building into a single theme, and

ascribes the evolution of earth’s surface morphology to relative angular motions of rigid lithospheric plates, lithosphere being the Earth’s ~150 km thick rigid outermost shell that includes the entire crust and the top part of the mantle.

This is needed in order to reconcile the facts that the ocean floor:

that covers ~70% of earth’s surfaces is basaltic, and therefore formed by the volcanic process

is 200 Ma old or younger (indeed, about 70% of the present seafloor has ages <100 Ma), compared to <4.2 Ga age of continental rocks; and

has existed through much of the earth's history;

Visit the site moorlandschool for an interesting presentation on plate tectonics

whereas all the evidences suggest that earth has not expanded appreciably during the past ~200 Ma period.

We clearly need a mechanism to explain these seemingly conflicting evidences and the postulate of global plate tectonics provides that.


A Closer Look at Earthquakes

The Plate Tectonics Postulate

ascribes the evolution of earth’s surface morphology to relative angular motions of rigid lithospheric plates, lithosphere being the Earth’s ~150 km thick rigid outermost shell that includes the entire crust and the top part of the mantle; and

thus explains how the creation of new surface area as an ocean floor is balanced by the loss of an equal surface area elsewhere, in a folded mountain belt or a deep sea trench.

The boundaries of these plates, shown in the animation below, are essentially seismic.

	Read the USGS Online publication 'This Dynamic Earth' above.
	Access Continents on the Move, a PBS/NOVA production on past continental configurations.
	Read David Sandwell's Exploring the Earth from Mars, to learn how space exploration can help understand the earth processes.

The plate boundaries are classified as either active or passive, depending on whether or not the surface area changes.

Active plate boundaries are where the surface area changes. Here,

divergent plate boundaries are where new surface is created, by way of seafloor spread ― these are the mid-ocean ridges and rises; whereas the convergent plate boundaries are those where the existing surface is destroyed, as at the folded mountain belts and deep sea trenches.

Three kinds of tectonism are possible at these convergent plate boundaries:

Folded mountain belts form when both the crustal edges of the two converging plates are continental. Mountain belts like Himalayas and Alps are the examples of this kind of plate boundaries. Seismicity here tends to be of shallow focus but high magnitude. Not surprisingly, the crustal thickness beneath the Himalayas is about 70 km, i.e., double the thickness of average continental crust, and about 50 km in the Alps!

Deep sea trenches form when the crustal edges of both the converging plates are oceanic. Mariana Trench, Tonga Trench etc. are the examples of this kind of a plate boundary. Needless to stress, seismicity here tends to have deep focus and high magnitude. For example, the world's most devastating tsunami in recent times ― the Boxing Day 2004 Asian Tsunami ― was produced by a magnitude 9.3+ temblor in the Java trench, off the island of Sumatra.

The deep sea trenches are also accompanied with volcanism on the subducted plate, as is clearly seen in this map of the Pacific 'ring of fire' (click on this image to learn more about this). This is because when the advancing wedge of the subducting plate melts, buoyancy prevnts continued subduction and the melt now rises. For the convergence of the oceanic crustal edges of two converging plates, this creates 'island arc volcanism'.

When the crustal edge of one of the converging plates is oceanic and that of the other one is continental, the result is a folded mountain belt at the continental edge and a deep sea trench at the oceanic edge. Examples? Note, for instance, that Andes Mountains define the Pacific coast of South America whereas Peru-Chile Trench defines the South American coast of Pacific ocean.

Clearly, (a) mountain belts form when continental crust is one of the converging edges, whereas
(b) deep sea trenches form when oceanic crust is one of the converging edges.

The passive plate boundaries are those where we have no change in the surface area, i.e., neither new surface is created (as at the divergent plate boundaries) nor is the existing surface lost (as at the convergent plate boundaries).

Examples:

Transform faults like the San Andreas Fault, and

Computing the displacement rate

If you think that the sluggish geological processes are hard to measure on human timescales, think again. Look at the displacement of Miocene sediments (say about 25 Ma in age) on the two sides of the San Andreas Fault, by say about 600 km. This implies a displacement at the rate of

600 km	=	600 x 10⁶ mm	= 24 mm/yr
25 Ma		25 x 10⁶ yrs

This approximately 1 cm/yr rate is easy to verify by physical observations and suggests that you need to wait another 25 Ma before UCLA and UC Berkeley can possibly become immediate neighbors!

fracture zones (offsetting the mid-ocean ridges)

are typical examples of such boundaries, at which the displacement is mostly lateral. Seismicity here has shallow focus but can have high magnitude.

Sediments

What are they, really?

Sediments are unconsolidated particulate materials that either precipitate from or are deposited by a fluid (e.g., water, wind, ice).

Geological materials comprising the sediments thus come either
(a) from the weathering and decomposition of preexisting rock materials that are subsequently eroded, transported and deposited in the basins, or (b) can be organic detritus.

These preexisting materials are either integral to the “rock cycle” and may be either primary (or igneous, i.e., plutonic and volcanic) or secondary (i.e., sedimentary and metamorphic) or may be organic.

See an animation model of the evolution of "West Central South America from the Early Jurassic to Late Miocene, with Some Oil and Gas Implications" by Terry Li Arcuri and George H. Brimhall at the URL: http://www.searchanddiscovery.net/documents/arcuri/images/Ev10o.gif.

Why do sediments matter?

Sediments (a) provide information about the past depositional environments and climatic conditions (b) corroborate inferences from such other data as marine magnetic anomalies, and (c) are important in terms of resources.

Recall, for instance, that based on the evidence of ~200 Ma old limestones that form the Himalayan peak Mt. Annapoorna, we know that an ocean once existed where now have the mighty Himalayas. Likewise, the ~250 Ma old Kaibab Limestones form the floor of most of the Kaibab National Forest which also houses of Grand Canyon, suggest that today’s arid Southwest was once a marine region.

Corroboration of marine magnetic interpretation has been a very interesting application of the sediment data. Sketched alongside, for instance, is the profile model across a mid-ocean ridge from which it can be seen that the age of the oldest sediment overlying the basaltic seafloor should be younger than, or at the most the same as, the age of the basaltic seafloor. As described below, this is exactly what the DSDP (deep sea drilling project) results show.

The map alongside shows the South
Atlantic drill sites under Leg 3 of this project, together with the ages obtained from interpretation of marine magnetic anomalies here.

The graph below compares these magnetic ages with the fossil-based or paleontological ages of the oldest sediments drilled at the Leg 3 sites 14 through 21. Note the excellent correlation between the two independently determined age data. These data themselves are tabulated below.

The total thickness of marine sediments

The map below shows the total thickness of world's marine sediments, as estimated from the seismic and deep sea drilling studies. They yield an average thicknesses of ~900 m over the entire ocean, shallow and deep (deep oceans have a substantially thinner layer, as almost 80% of these sediments are found on the continental margins).

For the 361 million km² total surface of the world ocean, this yields a total volume of 325 million km³. For an average sediment density of 2300 kg/m³, this means a total mass of about 750 x 10¹⁵ metric tons for all the marine sediments. At the hydrological cycle's annually averaged rate of depositing 15 million tons of sediments into the oceans, this means that all these sediments have taken about 50 Ma to pile up!

This ~50 Ma estimate of the time needed for present marine sediments to pile-up is barely a quarter the 200 Ma that we found earlier as the time that run-ff part of the hydrological cycle needs to fill the ocean basins. But this is only to be expected. Note that the process is a dynamic one. New surface is continually being created, after all, as the existing one is lost.

Download this map at http://www.ngdc.noaa.gov/mgg/image/sedthick9.jpg

The kinds and distribution of marine sediments:

Fascinating as this picture is, it hardly tells us the whole story. To

Seawater Chemistry

The water molecule

	Browse the “Periodic Table of Elements” here
	Read 'Elements, Isotopes and Radioactivity' at http://minerals.cr.usgs.gov/gips/na/0radio.htm#radio

There are over 300 million trillion gallons of water on earth ― if we divided it evenly, each person would have 40 billion gallons to themselves. To learn more about water and it's amazing properties, check out this HowStuffWorks video: How Water Works.


(1:55)

The atom of an element

is the smallest possible particle of an element that retains that element’s properties; and

has a nucleus, with protons and neutrons inside it, and electrons in orbit, there being as many electrons in orbit about the nucleus as the number of protons inside the nucleus (i.e., at its simplest, atomic number = number of electrons or protons, atomic mass = number of protons and neutrons).

Example:

Oxygen’s atomic number = 8, atomic mass = 16.
Thus an oxygen atom carries 8 protons and 8 neutrons in its nucleus and 8 electrons in orbit about the nucleus.

Hydrogen (H)	Visit the URL: http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm to learn more about the atoms and atomic structure. These animations on the left, taken from this website, illustrate the structures of two hydrogen isotopes, hydrogen (atomic number = 1, atomic weight = 1) and deuterium (atomic number = 1, atomic weight = 2). Tritium is another hydrogen isotope, not shown here, with atomic number = 1 and atomic weight = 3. Here, red denotes protons, blue the neutrons and gray electrons. Note that the hydrogen isotope lacks a neutron: it is basically a proton in the nucleus about which a single electron orbits, whereas the deuterium atom carries one neutron in its nucleus, in addition to the proton of course.

Deuterium (²H)


		Electron	Proton	Neutron

Nuclear Fusion Note that when we argue, following the most widely held view of solar system's evolution that was first proposed by Kant and Laplace, that all the matter evolved from Hydrogen, we are basically talking of the nuclear fusion of deuterium and tritium atoms. Indeed, the nuclear fusion of light elements is the energy source which causes the stars to shine. The animation on the right shows how the helium atom (He, atomic number = 2, atomic weight = 4) forms from the fusion of two deuterium (²H) atoms.	²H

		=



	²H		He

Question:

The fusion of how many deuterium atoms would create a carbon atom? nitrogen atom? oxygen atom?


	.

Coasts and the coastal processes

Watch the video "The Earth Revealed episode 'Waves, Beaches and Coast'

Why do the coasts matter?

We humans are littoral creatures, and therefore inhabit the shorelines, whether seashore, or lakeshore or riverside, as this map shows. Clearly, we are always affected by, and should be always concerned about, the processes at the coasts.

Earthquakes and Megacities:

This map shows major earthquake epicenters (red dots) and their relationship to world cities (white dots. Notice how well their locations correlate. Why? Use this map to learn about the distribution and frequency of earthquakes, comparing the earthquakes to the distribution of land masses, oceans, and cities/population. What cities are most at risk from earthquakes? How does your own city compare to others in terms of earthquake risk? On this map, over 39,000 earthquakes are shown with more than 8,300 cities.

Source: http://education.usgs.gov/common/resources/mapcatalog/images/earthquake/world_seismicity.jpg

Coasts can be

	active (i.e., plate boundaries) or passive (i.e., non-tectonic), and
	erosional (stream erosion, wind abrasion and glacial activity, e.g., fjords, or erosion by waves and currents, e.g., the effects of surging, plunging and and spilling breakers) and depositional (i.e., beaches, deltas etc.)

Ocean Cliffs:

From the archives of Discovery: Over time, these cliffs are worn down into unique formations. Learn more about cliffs and erosion here.

Human modification of the coast ― Construction in the coastal zone may enhance or otherwise alter the natural processes and their resulting impacts. Roads and beach-access paths perpendicular to the shore which penetrate the dune line may become overwash passes or focal points for storm-surge flood or ebb currents. Seawalls may redistribute wave energy or obstruct sediment movement. Jetties may block great volumes of sand from being transported along the coast, resulting in deposition of sand and beach widening on the updrift side and a long-term sand deficit and erosion on the downdrift side. Ground-level houses and closed-in ground floors of houses on stilts may obstruct the passage of overwash sand which is then lost to front-side erosion. Where vegetation cover has been removed, erosion by wind or water may occur.

http://coastalhazards.wcu.edu/Libros/libroschapter3.htm

> Primary producers are the plants that make food usually from sunlight.
> Capture and Flow of Energy:
> Photosynthesis: storing of energy, how it works, the reactions involved, more common.
> Chemosynthesis: storing of energy, how it works, the reactions involved, less common.
> Respiration: releasing of energy, how it works, the reaction involved,
> Flow of Matter between Life and Non-life: what matter is involved (O2, CO2, etc.), how it flows.
> Feeding (trophic) relationships:
> Primary producers (autotrophs) - plants
> Primary consumers and secondary consumers (heterotrophs) - animals.
> Trophic pyramid and food web: what they are and how they are laid out, producers and consumers.
> Primary productivity: where it is the greatest and the least in the oceans, where it varies most by season..
> Factors that limit productivity: CO2, water are not limiting factors, sunlight and nutrients can be.
> Plankton: what is it, phytoplankton vs. zooplankton, global distribution.
> Compensation depth: what is it, how is it related to productivity.
> Large marine producers: algae (primitive plants) vs. marine angiosperms (like most land plants).
> Algae:
> Nonvascular plants (no vessels): pick up water and nutrients along plant rather than in roots.
> Accessory pigments: affects absorption of light: other colors than green better deep in ocean.
> Other colors make algae have more photosynthesis deep in ocean.
> Marine Angiosperms: like "normal" plants - include sea grasses and mangroves.

Chapter 15: Marine Animals

> Beginnings of life up to free oxygen in atmopshere.
> Phylum similarities and major animal phyla (Table 15.1)
> Invertebrates vs Vertebrates - differences, relative numbers.

> Invertebrates:
> For each of major phyla of simplest invertebrates: types of animals and basic characteristics.
> For each of major phyla of advanced invertebrates: types of animals and basic characteristics.
> Mollusks: 3 classes of mollusks: types of animals and basic characteristics.
>Arthropods: types of animals and basic characteristics.
> Chordates: types of animals and basic characteristics.
> Echinodermata: types of animals and basic characteristics.

> Vertebrates:
> For each of major phyla of vertebrates: types of animals and basic characteristics.
> 3 phyla of fishes: types of animals and basic characteristics.
> Amphibeans: why there are basically no marine amphibeans.
> Marine Reptiles: types of animals and basic characteristics.
> Marine birds: types of animals and basic characteristics.
> Marine mammals: types of animals and basic characteristics.

Chapter 16: Marine Communities

> What is a marine community?
> Relationship between community, habitat, and niche.
> What is biodiversity?

> Influence of Physical and Biolgiocal Factors:
> Examples of Physical and Biolgiocal Factors
> Responses of organisms to range of factors - optimal range, etc.
> Competition between organisms: same species, different species, native vs exotic species.
> Growth rates and limiting factors.
> Distribution of organisms within community: random, clumped, and uniform.
> Changes in communities including climax communities.

> Examples of Marine Communities:
> Basics of each marine community including characteristics and locations (near Florida?).

> Symbiosis: what it is and the 3 types.


Cool Underwater Creatures

	The atmospheres of Venus and Mars are carbon-rich, with ~90% CO₂. Earth's present-day atmosphere is significantly different, and contains only ~0.035% C, but had about the same CO₂ once upon a time as the venusian atmosphere today.
	The densities of the three atmospheres are significantly different, however ― Venusian atmosphere is ~90 times thicker than Earth's atmosphere whereas the latter is ~90 times thicker than the Martian atmosphere!

	As for the hydrological cycle on Mars, there is good evidence that water was once abundant enough on Mars to have produced the landscape we now see but now remains confined to the subsoil and the polar ice cap. The question, then, is as to how and why might Mars have lost its hydrological cycle.
	A good chance is that Mars is too small to have had a strong enough gravitational field that would have prevented water from escaping into the space. It is not that Martian atmosphere is not thick enough ― the total quantity of CO₂ in the Martian atmosphere greatly exceeds that in the Earth's atmosphere, after all. It is just that the planetary atmosphere must have some mechanism to prevent the escape of water into the outer space. Unfortunately, though, appealing to low density of Martian atmosphere to argue that its temperature gradient is too gentle to have prevented the escape of atmospheric moisture (unlike Earth’s tropospheric thermal gradient that is steep enough to have retained the hydrological cycle), ignores the fact that a vigorous hydrological cycle may have once existed on Mars.
	There is also some evidence that plate tectonics once occurred on Mars, but no longer does. The question is whether the striped magnetic anomalies reported on Mars that seem so similar to those seen on Earth's oceans indeed provide the evidence of now defunct but once active Martian plate tectonics. Also, if indeed so, the question is whether these anomalies formed 4 Ga ago or about 1000 Ma ago. We could nonetheless claim that Mars lacks hydrological cycle because it no longer has the plate tectonics to create new ocean basins to replace the ones flattened by the “run-off” component of hydrological cycle.
	The presence of hydrological cycle on the Earth, and its absence on Mars, is therefore due as much to the planetary atmospheres as to plate tectonics, much as the case is with Venus.