Monday, 20 August 2012

The sucking sound in the ground

Groundwater hold in aquifers is a life-sustaining resource that supplies directly water to billions of people, for drinking, daily domestic use, agriculture and livestock. About 1.7 billion people live in areas where groundwater resources or groundwater-dependent ecosystems are under threat because of their over-exploitation. Thus, almost one-quarter of the world’s population lives in regions where groundwater is being used up faster than it can be replenished. Often it is a resource that was built-up under past climates as the Nubian Sand Stone aquifer under the Sahara.

Fields irrigated with water from Ogallala aquifer
Often aquifers are over-exploited in are areas in which precipitation is scare or seasonal and  thus productive agriculture requires use of ground water, such as in the west of USA where agiculture is supported by the Ogallala aquifer. There use of ground water plays a central part in irrigated agriculture and  rising livestock that requires large amounts of water.  Likewise, presence of ground water is "just" beneficial for the health of many ecosystems, as for example it hinders intrusion of seawater into coastal plains.

Across the world, human civilisations depend largely on tapping vast reservoirs of water that have been stored for up to thousands of years in sand, clay and rock deep underground. These massive aquifers — which in some cases stretch across multiple states and country borders — provide water for drinking and crop irrigation, as well as to support ecosystems. Modern pumping technology and traditional property laws make water in these aquifers cheap and accessible to industrial agriculture. 
Water level drop up to 40 feet (deep brown)
between 1980 1nd 1995
Un-sustainable depletion of groundwater is described by a “groundwater footprint” [1]. The "groundwater footprint" is the area required to sustain groundwater use and groundwater-dependent ecosystem services. Currently humans are over-exploiting many large aquifers that are critical to agriculture, especially in Asia and North America  including many of the world’s major agricultural regions;  in the Central Valley in California, the Nile delta region of Egypt, and the Upper Ganges in India and Pakistan, demand exceeds these reservoirs' capacity for renewal.

The size of the global "groundwater footprint" is currently about 3.5 times the actual area of aquifers [1] because 20% of the world’s aquifers are being massively over-exploited. For example, the groundwater footprint for the Upper Ganges aquifer is more than 50 times the size of its aquifer.

Ukko El'Hob

Reworked from:

[1] Water balance of global aquifers revealed by groundwater footprint; Tom Gleeson, Yoshihide Wada, Marc F. P. Bierkens & Ludovicus P. H. van Beek & Groundwater use is unsustainable in many of the world's major agricultural zones. Amanda Mascarelli, NATURE,  08 August 2012

Tuesday, 7 August 2012

Folding Earth's Timeline

Evolution did a great job. Although, it took its time – 4.7 Billion years.  But how long are 4.700.000.000 years ? Any chance to feel how long is that elapse of time ?  How to fold that line of millions, billions of years so that it feels like a human timeline? 

Marine Fossil Biodiversity since half a Billion years
(from Wikipedia)
What about counting years of Earth history as seconds of human life? Sixty seconds add to a minute, three-thousand six-hundred seconds add to an hour, eighty-six-thousand our-hundred add to a day, and thirty-one-million-five-hundred-thirty-six-thousand seconds add to a year (1); and so on.

A second feels like an elapse of time that we know. A year feels like an elapse of time that we know  too. A year counts for many seconds, namely thirty-one-million-five-hundred-thirty-six-thousand; what sounds “a lot”. That “thirty-one-million… number” does not feel specific, although a year feels specific and a second feels specific too.  So, feeling a second, feeling a year and feeling the difference between both elapses of time gives a quite particular spread of perception of how much that “thirty-one-million… something” is.  That spread of perception could be used to fold the timeline of Earth’s history onto a human timeline. 

A fairy tale…?

Thus, imagine to count a year as “a second of Earth's life”. Then, "a minute of Earth's life” would make most of a human life time. "An hour of Earth's life” would cover most of the period for which we, humans have some written records. "A day of Earth's life” would go back to times when our human species had evolved in Africa, just more or less ready to conquer the globe and to replace other human species. And "a year of Earth's life” would go back before modern fauna evolved, before continents had drifted to their present positions, before rapidly cooling Antarctica had become more isolated, and before the Antarctic Circumpolar Current had to start flowing. Thus within "a year of Earth's life” major biological, climatic and geological changes of the earth system occur.

Acasta gneiss, one of the oldest rocks on Earth. (2)
Counting a year as a “second of Earth's life” folds Earth’s history on timeline that can be captured by human perception. Counting 4.7 Billion years as 4,700,000,000 “earth-seconds” make hundred-forty-nine “earth years”. A human life would last 60 to 90 “earth-seconds”. Earth would have an age of 65 Million times the span of a modern human life. An enormous number, but counting only hundred-forty-nine “earth years”. One and a half century, that our perception can capture: it is back to times when grand-grand-parents were young, who are known from pictures made when they were old.

Ticking years as “earth-seconds” fold the time line of Earth history such that it looks imaginable for a human mind: It is mapping Earth's history on the lifespan of our grand-grand-parents, grand-parents, parents, us and our children. Thus four or five generations to illustrate the painstakingly long periods that have passed since earth formed out of stellar dust, since very first forms of life emerged, since more complex organisms emerged, and finally human beings conquered the globe.  

Fold one...- how long is a Billion or two?

Our planet, Earth evolves since about 4.7 Billion years since it formed as ball melting old stellar dust and ice into something new. Ticking years as “earth-seconds” Earth started to form nearly 150 “earth years” ago. A Billion “earth-seconds” counts for little less than 32 years.

Stromatolites at Hamelin Pool, Shark Bay.
Photo by Paddy Ryan
Ticking years as “earth-seconds", Earth emerged from stellar dust as grand-grand-parents were born. During their childhood Earth grew by more and more aggregation of interstellar dust and ice. Messengers from that time are iron-nickel meteorites that still today hit the Earth. When grand-grand-parents were youngsters the surface layer of the Earth cooled so far that rocks formed, first heavy basalts that are recycled  and then lighter granites and gneiss.

The oldest  rocks, Acasta Gneiss (4.3 Billion years) can be found in Canadian Northwester Territories.  Since chemical evolution of Earth was spinning up. And just about when grand-parents were toddlers, a Billion years of chemical evolution had lead to living cells (cyano bacteria). They were releasing oxygen into the world and evolution of Earth was made spinning faster. Living slim started to cover the rocky shores of the ocean. Since that time Stromatolites (3) are on Earth, from most ancient times until today. Once a sufficient amount of oxygen had been produced iron got oxidised and large iron ore deposits formed on Earth. Grand-parents were already old when the oxygen concentration in the atmosphere was approaching levels that we know today. Thus it took live span of two generations - about half the history of the Earth or more than 2 Billion years – to evolve from molten stellar dust to planet with reddish land, blue oceans and slimy live along the shore.

Fold two... -how long are some Millions?

Modern terrestrial animals, about as we know them, thus mammals exist since about 50 Million years. The geological epoch when they emerged (Eocene) started after 99% of Earth’s history had passed already. It started warm, and wide oceans created a moist global environment. Apart from the driest deserts forests were spreading from pole to pole and they would look reasonably familiar to our eyes. Dinosaurs had started off, lasted for more 180 Million years, and had disappeared well before. Trilobites in the sea had started off half a billion years ago, lasted for 300 Million years and disappeared before Dinosaurs.

Trilobite Genevivella grannulatus
50 Million seconds are close to one and a half year. 180 Million seconds are little less than 6 years, and 300 Million seconds little less than 10 years.

Ticking years as “earth seconds” and thinking in generations, the Eocene is part of a my very recent past; me being now 32 years. Dinosaurs I saw some years ago, as well as Trilobites as I was still an adolescent. Grandparents, as they were young have seen first Stromatolites and other microbiological mats along the shore line of the sea. Forefathers mostly knew rocks only, and witnessed bio-molecules emerging from more simple chemistry, but parents, I and my children saw and see life conquering Earth. 

Fold three...- how long is a Million or two? 

Evolution of our species;
~3,  ~1 and ~ 0.2 Million years ago
Early human beings (species "homo erectus") evolved about 1 Million years from earlier human-like species. These species evolved three to four million years ago leaving apes well behind them;

Ticking years as “earth seconds” one million seconds are a little more than 11.5 days, and four million seconds are about one and a half month.

Thus folding time scales – counting years as “earth seconds”, human beings emerged on Earth a little earlier this month, agriculture started just three hours ago, steam engine’s puffing was heard three minutes ago, and the first atom bomb blow up a minute ago.
Watt's Steam-Engine  as granted a patent by Parliament

A fair story…!

So, our human history is a story of minutes or hours when it is counted in “earth seconds”. Counting "earth seconds", living plants and animals populate the planet since some years, at best since two decades; first in the sea and much later on land.  On the same folded time scale,  the beginning of microbiological life on our planet dates back hundred to hundred-twenty years from today, or up to four Billion “earth seconds” ago.

Thus evolution took its time and sized its chances. It is to us to preserve it in the anthropocene.

Ukko El'Hob

p.s. If you like to read more about Earth's history over billion of years then I recommend  "The Story of Earth: The first 4.5 Billion Years, from Stardust to Living Planet" by Robert M. Hazen.

(1) Approximating the year to 365 days. The sidereal years has 365 days, 6 hours, 9 minutes and 9.54 seconds, or 31,558,149.54 seconds.

(2) The contorted white bands in the Acasta gneiss consist of quartz and feldspar, two minerals common in granite. Their occurrence tells us the gneiss was metamorphosed from granitic rock contained in Earth's earliest continental crust. Most granite forms by melting of an older basaltic crust in the presence of water, rather than by direct melting of Earth's mantle. Thus, the Acasta gneiss provides indirect evidence for the presence of water on the early Earth, and for a basaltic crust that formed before 4.03 billion years ago. Photo by Chip Clark, NMNH. (Smithonian)
(3) Stromatolites are formed in tidal zones by colonies of cyano bacteria accumulating sand grains into layered structures.