6 April 2009

Visible and IR transmission of atmosphere This shows the visible sunlight and thermal IR emission and the wavelengths were different molecules absorb radiation.

Global Carbon Emission This shows the amount of carbon dumped into Earths atmosphere by burning fossil fuels (and making cement). Ove the past 100 years or so, humans have dumped about 250 gigatons of carbon into the atmosphere.

Earths carbon inventory The amount of carbon in various reservoirs on Earth. The atmospheric carbon is of 2000, and includes a contribution of about 1/3 from recent human activity (about 200-250 GT out of 720 GT). Note that by far the largest carbon reservoir is carbonate rocks, such as limestone (CaCO3). This is found primarly on the ocean floor, and the carbon in these rocks is sometimes recycled into the atmosphere by volcanoes.

CO2 content of atmosphere By burning fossil fuels, humans have increased the amount of CO2 in the atmopshere. Careful observations of CO2 (here plotted as ppmv - parts per million by volume) have been made from Mauna Loa HI (a place not much affected by "local" sources) for almost half a century. The observations show that the CO2 in the atmsophere has increased by about 1/3 over just the last half century.

Faint Sun "Paradox" Computer models of the Suns evolution predict that the Sun is slowly becoming more powerful. This means that the Sun was fainter in the distant past, and would not have kept the Earth warm enough for liquid water (all other things being equal). As we have fossil and mineralogical evidence for liquid water for most of past 3.5 Gyr, this realization was at first called the "faint sun paradox". But the obvious way out is that the Earths atmosphere was far different in the past. It is probable that the early atmosphere had MUCH more CO2 than todays atmosphere.

Possible CO2 vs time This diagram shows much more CO2 in the past than now. (How close to reality this is is not clear) This is one obvious way out of the "faint sun paradox"- the Earth had a much greater greenhouse effect in the past, and that allowed the less powerful Sun to produce a surface temperature that allowed liquid water over a large fraction of the Earths history.

The "Deep glaciations" mark times of possible "Snowball Earth Events" (you gotta have a catchy phrase for your discovery or hypothesis!). In an SEE, most of Earth (including oceans- at least surfaces) were presumably frozen. SEEs are hard to "recover" from, as the frozen Earth has a high albedo, causing even lower temperatures- also, the cold air can't hold much water vapor which acts like a greenhouse gas. SO, it sounds like a SEE is a one-way ticket to a frozen hell. Perhaps the humble CO2 (and CH4 = methane) molecules- spewed from volcanoes- could help break the SEE.

CO2- rock cycle Exchange of CO2 between atmosphere and carbonate rock reserviors may help moderate temperature fluctuations. If the CO2 gets "high", the Earth warms, there is more water evaporation and rain, which causes more rock weathering, which puts more CO2 into ocean, which decreases atmospheric CO2, which cools Earth.

Presumably, this general mechanism may help rid the atmosphere of the fossil fuel CO2, but the timescale to do so is FAR beyond human timescales (and the process of absorbing extra CO2 will alter ocean chemistry - ocean acidification- with at present unknown ramifications).

(1) Ice sheet extent (blue) - last Ice Age (2) Cape Cod - a gift of the ice The Earths climate undergoes various changes on different time scales. Some few 10,000s years ago, the Earth was colder than now, and thick ice covered almost all of Canada and the US upper midwest and New England. Many surface features in these areas can be understood from the action of the moving glaciers of the ice age. As just one example of that- my favorite "gift of the ice"- Cape Cod. Cape Cod is a terminal moraine feature. It marks the southern limit of one phase of glacier advance. As the ice "stalled" and then retreated, it left behind rocks and gravel it had pushed ahead of it, leaving the Cape and The Islands.

Temperature and CO2 history from ice cores Scientists can recover some information about the atmosphere in the past by looking at air bubbles trapped in layers of ice, particularly in Antartica. The air temperature can be surmised from isotopic ratios of oxygen. The plot shows that the Earth (or at least Antartica) was cooler by about 8C 15 to 20 thousand years ago (last Ice Age). The CO2 and temperature variations appear highly correlated- what this means is unclear (at least to drbill!)

20th century CO2 and history from ice cores The amount of CO2 in the Earths atmosphere in the past century is far above that of the past 0.5 million years.

(1) Activity (earthquakes, volcanoes) on Earth (2) Tectonic plates The Earths outer shell is divided into a dozen or so "plates" that move around. The plate boundaries are outlined by earthquakes and volcanoes.

Earthquakes on Earth Same idea as previous, but with lots more real data! This shows position of over *1/3 of a Million different earthquakes** over 35 years.

(1) Plate boundaries (2) Plate boundaries - spreading ocean floor to subduction zone (3) Subduction zone, ocean trench and orogeny - west coast of South America (4) San Andreas transform (slip fault) boundary There are 3 kinds of plate boundaries- converging, diverging and transform. At diverging boundaries (in oceans) "new" sea floor is made, which is then "lost" at converging boundary (subduction zone). By the way, "orogeny" has nothing to do with erogenous or orgy- orogeny means the process of mountain formation.

Age of sea floor This color- coded map of the ages of sea floor rock shows the spectacular success of the idea of sea floor spreading- you can clearly see the long linear "sources" of the sea floor rocks as the youngest rock (coded as red- make sure you look at the color-age bar in lower left).

(1) Continental drift (2) Pangea breakup animation The continents are lighter rock (mostly granite- about 2700 kg/m**3) that "float" on the denser sea floor (basaltic rock- about 3300 kg/m**3). The continents move about slowly.

Fossil map evidence of continental breakup Maps of fossils of ancient creatures show that the ranges of some creatures, presumably once contiguous land, are now split onto two continents- just what you would expect from continental breakup and drift.

Earthquakes in Fiji Sea and plate subduction By plotting position and depth of earthquakes in the Fiji Sea, we can "see" a subducting plate. This drawing shows the relationship between ocean trench, volcano and subducting plate.