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South of San Jose Costa Rica: On The Farm

Environmental Performance Index

Developed by the Earth Institute and Yale's School of Environment, while widely used by The World Economic Forum, the Environmental Performance Index (EPI, image at right) is the most meaningful set of criteria and system for ranking a countries "green" factor. In 2010, the countries ranking 1st, 2nd and 3rd were Iceland, Switzerland and Costa Rica, respectively. The United States ranked 61st.

Used by policy makers and environmental scientists as a benchmark index, the EPI has two general objectives; quantify leading indicators that affect:

i) environmental health

ii) environmental vitality.

Each objective has multiple indicators. Some examples of indicators for environmental health are adequate sanitation, drinking water, and urban particulates. Indicators for environmental vitality include things like irrigation stress, pesticide regulation, industrial carbon intensity and emissions per capita. To measure a countries EPI, indicator outputs are quantified and reported as metrics. Costa Rica's favorable EPI ranking is certainly due to a national commitment of being carbon neutral and environmentally progressive.

Costa Rica

Over the last three million years, the Central American land bridge has driven biotic exchange between the continents. In part, the unusual biodiversity observed in Costa Rica (topographical map left) has been due to the high frequency of biological migration, between the continents, through environmentally diverse locations.

Given converging plates in the Pacific’s Middle American Trench, just 40 miles west of the coast, volcanic activity has stretched a line from Guatemala to Panama. In Costa Rica, there are more than a hundred volcanoes, five of which are still active. The majority of the volcanism in Costa Rica ended around 5-8 million years ago and much of the region is covered by intrusive basaltic formations from past eruptions (image lower right). The plate subductions are expected to have resulted in metamorphism, but there is reported to be little indication of metamorphic rock as it's thought to be buried. The oldest rocks are around 180 million years old and were found on the western coast of the Nicoya peninsula. These old rocks, called ophiolites, have been identified just north and south of CIRENAS and are result of broken chunks of uplifted ocean floor.

12,000 years ago: Pleistocene ends

Whereas formation of the Isthmus of Panama marks the beginning of the Pleistocene epoch (3 MYA), the receding glaciers some 12,000 years ago mark its end. Just before it’s end, around 15,000 years ago, the glacial lake Hitchcock extended from beyond Hartford to St. Johnsbury VT. Having mapped river deltas that trace their flow into Lake Hitchcock, geologists have charted the lakes shore elevation to 300 feet above sea level (corresponds to the present elevation of Eaglebrook School that lies tucked into the Pocumtuck ridge, just east of DA). 15,000 years ago, Deerfield Academy was under water on what would have been the bottom of the lake, hypothetically shown in upper right image (Little and Sillin). Under 150 feet of icy, muddy, Lake Hitchcock water, the soils of present day Deerfield valley remained that way, underwater, against the backdrop of glaciers, for more than a thousand years.

From a human perspective, by 15,000 years ago hunter-gatherers are thought to have passed over the Bering Land Bridge and had become well settled in North America. As the glacial period continued, humans are thought to have passed from North America across the Isthmus of Panama and ventured into South America.

By 8000 years ago, with glaciers retreating, humans migrated back into the northeast and followed their icy retreat venturing north up into Canada, the Arctic Circle and then Greenland.

Richard Little speculates that glacial retreat (technically post glacial crustal rebound) may account for why the Deerfield River unexpectedly flows north in the rift whereas it’s master, the Connecticut River flows south. The image lower left (Little and Sillin) takes a southerly view through the present day Deerfield valley. Crustal rebound says, as the weight of a glacier compressed land underneath by hundreds of feet, more southerly regions would have had the glacial force removed first, given their northerly retreat. From this reasoning, southerly landscapes would be subject to rebounding before northerly landscapes. Moreover, Deerfield river water entering the rift would flow downhill in a north direction where it’s flow eventually met with the Connecticut River.

And what effect was the isthmus of Panama having on human travels during these corresponding times?

American farmers are thought to have emerged in present day Mexico between 3000-5000 years ago growing first squash, chili, then corn and then beans. These nomadic farmers continued from these regions, into South America.

In terms of cities, the first American ones are thought to have developed along the Gulf of Mexico some 3200 years ago. Of course, this frame of time corresponds to the Trojan War, Hebrews moving through Egypt and the Shang Dynasty in China.

Cocos/Caribbean plate subduction

The map on the right shows digital elevation land mass of Central America, and sea floor of Cocos, Nazca and Caribbean plates. Moving Northeast at 10 cm/year, the Cocos plate is subducted beneath the Caribbean plate resulting in the volcanism. From this same image Jeff Marshall has noted the boundary between the smooth sea floor associated with the Cocas plate and the rough elevation below sea (Nazca plate) that bounds to the southeast.

Shown lower left is the boundary of the Middle America Trench (purple) off shore of Nicaragua and Costa Rica's Nicoya Peninsula. The Trench is even more dramatic in 3-D from the perspective looking East at the subduction zone (image lower right).

3 MYA: The Isthmus of Panama and Pleistocene Ice Age

An ice age is a generic term used to describe a reduction in Earth temperature, expansion of ice sheets and glaciers. Evidence obtained from chemistry, geology and the paleontological record indicate there have been at least five major periods of ice ages on Earth beginning around 2.4 BYA, 850 MYA, 450 MYA, 350 MYA and the most recent 2.6 MYA.

One trigger for this most recent ice age is considered to be the creation of the Isthmus of Panama. Formation of the isthmus is thought to have begun around 20 MYA. Again for perspective remember that by 20 MYA dinosaurs (having emerged 200 MYA) had already been gone for 45 million years.

The Isthmus of Panama seems to have occurred when land on the western Caribbean plate, now described as Central America, overrode the Cocos plate located in the Pacific Ocean. From the map of plate tectonics (image upper left) the proximity of the Caribbean, Coccos and Nazca plates can be observed along Costa Rica in Central America. During this subduction event the Cocos plate was pushed downward below the Caribbean plate and given exposure to internal heat, becomes molten rock. The building pressures from subductions result in lava and hot gasses that rise underneath the Caribbean plate producing volcanoes.

A map of ocean trenches in the Pacific show the presence of the Middle America Trench (image lower right).

All along the Middle America trench, undersea volcanoes erupted until peaks emerged above sea level. As land mass continued to increase and a connection between North and South America emerged, the Isthmus of Panama was formed.

Prior to formation of this isthmus, warm water currents had run north along northeastern South America through the Caribbean and into the Pacific. With emerging Central America acting as a land bridge, warm northerly flowing ocean stream water was deflected through the Gulf of Mexico reinforcing the Gulf Stream that brings warm waters to North Americas East Coast.

Two conditions are thought necessary for an ice age, cool continental temperatures and air moisture for falling snow. Speculation suggests that by diverting the flow of warm Atlantic waters from the Pacific into the North Atlantic that the Pleistocene ice ages may have been triggered. The Pleistocene ice age generated massive glaciers that covered northern lands and provide much of the recent geological structure observed in Deerfield today.

In terms of adding perspective to a time frame of 3 million years ago, Australopithecus was roaming Africa 2-4 MYA and around 2 MYA Homo erectus is thought to have emerged.

200 MYA: Pangaea breaks apart & New England shows faults

As bedrock folded under Pangaea's formation, other zones that had melted as result of subductions, cooled. Slowly, molten rock cooled into the granite that marks the V-shaped Deerfield valley.

Then, in what would be opposite the motion that caused formation of the super-continent, 200 million years ago, Pangaea began breaking apart. Stress from the super-continental separation created the Eastern Border fault that runs through New Hampshire, Massachusetts and Connecticut. Stress, from this fault zone led to development of a rift valley where sediment was deposited as shown by the image upper right (developed by Richard Little and Will Sillin). Whereas the block diagram of the rift valley was caused by geological events from 200 MYA and shows modern day river systems, it's worth remembering that these river systems are thousands of years old, not millions. Older granite and metamorphic rock underlies the rift and can be observed in far western and eastern Massachusetts, sediment flowed into the rift. This sediment is younger rock, largely red Arkose (sandstone containing feldspar, an aluminum silicate). In Deerfield, red arkose is readily seen along the Pocumtuck Range.

250 MYA: Forming Pangaea - Deerfield's in the Middle

Around 500 million years ago, the super continent Pangaea had yet to form. At that time, geologists believe that what is now the North American shoreline ended near the eastern New York border and almost none of the land that today define as New England was attached to North America. Instead, the land masses of Deerfield and surrounding New England were big islands on the earths crust called exotic terraces. During the collision between the African, European and North American continents these terrace were smashed between North America and Western Africa, forming Pangaea (image top right).

In terms of how we know what we know, Raymo tells interesting stories revealing that when the first reasonably accurate maps of the Atlantic Ocean were drawn in late sixteenth century, people noted that the two sides of ocean continents matched like jigsaw puzzle pieces. Largely from the observing similar rock formations along the eastern coast of South America and the western coast of Africa, the German meteorologist Alfred Wegener proposed in 1915 that all the continents were once united in a supercontinent, Pangaea. Wagener proposed that Pangaea broke apart with continental drift accounting for the present positions. His theories were examined, then rejected by prominent geologists of the time. It was not until much after his death in the 1960s when continental drift and the theory of Pangaea was revived.

Raymo continues the story recounting that the technology of echo sounding (sonar) made possible the mapping of the sea floor that revealed a system of ridges on the ocean basins. Apparently, if it were possible to drain all the water from the oceans, as when emptying a bathtub, the undersea mountain ranges would be the most dramatic of all global ranges. In the Atlantic, the ridge lies exactly in the middle of the ocean basin and at this ridge there is an outflow of heat from the earths interior. The outflow of heat yields seafloor rocks that are youngest at the ridge and oldest near the continental margins. American geologist Harry Hess in 1962 took these observations and developed the theory of sea-floor spreading. Hess maintained that the entire earth crust is cycled through the earth’s interior every several hundred million years. This great looping motion of matter is driven by heat convection in the Earths interior – by the tendency of hotter matter to rise and cooler matter to sink in these great convective loops (image upper left).

As the continents collided forming Pangaea, subduction occurred where one place slid underneath another and forced bedrock upwards, generating the Appalachian Mountains. These mountains, once the size of the great Himalayan ranges today, folded and deformed the deep bedrock into metamorphic rock types gneiss, schist, slate and marble. As these continental collisions and folding bedrock occurred, other subterranean zones that had melted cooled slowly, crystallizing into granite that underlies the Deerfield Basin.

For perspective on these geological events it’s worth considering geological time put into a geological clock (below). Earth began at 12:oo, life at 2:00, photosynthesis at 3:00, oxygen rich atmosphere at 6:00, eukaryotes at 6:30, cambrian explosion at 10:00, Pangaea forming at 11:00, with the arrival of dinosaurs shortly to follow.