Earth


Earth is located third from the Sun, its orbit of 149,597,890 kilometers or 1 AU (astronomical unit) placing it well inside the Solar System’s habitable zone, [1] its diameter of 12,756 kilometers making it the fifth largest body (excluding the Sun) in the solar family.

Humanity's home is known by many names (Earth, Terra, Gaia, Tellus, Ersetu or Honua just a few of the hundreds spanning time, culture and religion) but whatever it's called one salient fact is evident, conjecture aside it’s all we have and not just us humans but all life, because at this point in time, to the best of our knowledge, we’re all alone. Earth is the only planet in the entire universe that we can say with certainty harbors life.

The planetesimal theory of planetary formation hypothesizes that the Earth was created some 4.6 billion years ago with the contraction of a stellar nebula into larger and larger clumps of matter, the gas, dust and debris eventually coalescing into the Sun, planets and moons that comprise the Solar System.

Earth has an inner core, mostly iron, with a temperature of between 4,000 and 5,000 degrees Celsius, surrounded by an outer core, then a mantle, both in a semi-fluid state, surrounded by a crust comprised of solid plates constantly in motion floating on the mantle (there are eight major and numerous smaller plates, intense seismic activity most often occurring in areas where they interact).

Seventy-one percent of Earth’s surface is covered in water, the only planet in the solar system where surface water in large quantities exists in liquid form. The rest is land, everything from low lying islands barely above sea level, to towering mountain ranges, plateaus and vast plains.

Earth’s atmosphere is an envelope of gases, thicker at the bottom then gradually thinning before fading into outer space (the Karman Line at one hundred km from the surface is generally considered the outer boundary); it consists of nitrogen seventy-seven percent and oxygen twenty-one percent, with carbon dioxide, argon and water comprising most of the remaining two percent. The amount of carbon dioxide is critical in the maintenance of Earth's surface temperature; its what’s called a greenhouse gas and along with water vapor is responsible for what is called the greenhouse effect (the same effect that heats up your car when you leave the widows closed on a sunny day). Too little and the temperature would plunge and we and the oceans would freeze. Too much and the temperature increases with catastrophic results, droughts, massive storms, hurricanes of immense destructive power, melting ice caps and loss of habitat as sea levels rise.
 
The Precambrian is the name given by geologists to a period that began over four billion years ago; it was a violent era of intense meteor bombardment and constant volcanism, a time when a hot lifeless atmosphere of nitrogen, carbon dioxide, hydrogen and water vapor enshrouded the planet. Then as the Earth cooled plate tectonics began defining the planets surface, water vapor condensed fell as rain and oceans formed.

Three and a half billion years ago life appeared, Archaea, one celled organisms that reproduced by dividing (asexual reproduction) and didn’t require oxygen to create energy. These were followed by cyanobacteria, which gradually introduced oxygen into the atmosphere through a process called photosynthesis. Later came eukaryotes an evolutionary jump, these were organisms with a nucleus in their cells that reproduced by combining their genetic makeup. Then near the end of the Precambrian another evolutionary jump, a group of organisms known as the Ediacaran fauna appeared a forerunner to the flood of life forms that was to follow.

Approximately five hundred and fifty million years ago in a time called the Cambrian period (the earliest period of the Paleozoic era) an event took place which came to be known as the Cambrian explosion. Life began to diversify and increase in complexity at an astonishing rate, almost all the main groups of animals known today first emerging. Later in the Paleozoic fish appeared in the sea and multicellular plants, insects and amphibians appeared on land. It was a time of trial and error for Mother Nature, new forms of life made an appearance and flourished, while others unable to compete disappeared, mute testimony to natural selection and the survival of the fittest. The Permian period closed out the Paleozoic, reptiles were dominant, the first mammal like reptiles came into existence and fern-like forests covered the land.

Then suddenly it was over, a catastrophe of global proportions triggered the greatest mass extinction in history and ninety percent of life on the planet was gone. What caused it is still unclear, a comet or asteroid impact, a major volcanic event or a nearby supernova are all possibilities.

The Mesozoic begins in the ashes of the Paleozoic and is divided into three geological periods called the Triassic, Jurassic and Cretaceous. It is often referred to as the Age of the Dinosaurs because these animals overwhelming dominated the land, sea, and air. Domination acquired as they filled vacant ecological niches left by the mass extinction of the late Paleozoic, niches that were also filled by birds and mammals, while flowering planets replaced conifers as the dominant vegetation. It was also the period in which the giant supercontinent of Pangaea began to break up into separate land masses.

During the Late Cretaceous the dinosaurs may have ruled and Tyrannosaurus Rex may have roared, but it was the small rodent like mammals that burrowed underground or scurried in the shadows whose unique physiology and way of life was about to guarantee them a place in the sun.

The Cenozoic era began about sixty five million years ago and is divided into the Tertiary and Quaternary periods, the latter being both a time of great ice ages and a time when plate tectonics and continental drift defined the Earth’s surface. The Mesozoic was the Age of Dinosaurs; the Cenozoic is the Age of Mammals. The boundary between Mesozoic and Cenozoic was abrupt and catastrophic, brought about by an event so devastating that it changed the world, caused mass extinction and ended the dinosaurs one hundred and eighty million year reign.

It probably began as a giant fireball streaking across the sky and then impact a ten km wide asteroid slamming into the Yucatan with a force of one trillion megatons. Vaporized rock and debris are hurled high into the atmosphere a massive firestorm sweeping outward from the detonation trees and animals in its path exploding into flame. The crust ruptures as intense volcanism spews forth magma, earthquakes follow triggering giant megatsunamis which race throughout the world’s oceans swamping coastlines with thousand meter high walls of water. The sun vanishes as smoke, toxic soot and ash envelope the globe. Plants and animals die from the cold as temperatures plummet and a long nightmarish winter begins. Finally after several years the atmosphere begins to clear and the sun peaks through the haze. The temperature starts to rise, but it’s not over yet, increased carbon dioxide causes a runaway greenhouse effect that threatens to cook whatever has survived. The smaller animals that had huddled in their burrows for warmth dig deeper as they now seek to stay cool, until eventually, as temperatures begin to revert to past more tolerable levels, the survivors emerge but into a changed world. The dinosaurs are gone; the age of mammals has begun.

Man has been on this Earth a relatively short length of time. The fossil evidence seems to indicate that he began to evolve in Africa between five and six million years ago and began to migrate eastward about one and a half million years ago.

New studies by the Genographic Project, a joint venture between IBM and National Geographic, uses DNA samples gathered from indigenous groups around the world in order to trace the migration of early humans from when they first left Africa sixty thousand years ago to the present time. Though controversial the evidence as presented suggests that all present day humans (Homo sapiens) descended from a single common ancestor who lived in Africa some sixty thousand years ago.

Essentially it postulates that the migrations took place in waves: The first wave colonized Australia about fifty thousand years ago; the aborigines are their descendants. A second wave colonized the Middle East, India and China about forty-five thousand years ago and following the retreating glaciers moved into central Asia about forty thousand years ago. Small groups later migrated into Europe around thirty five thousand years ago, coming into contact with and eventually replacing and/or interbreeding with Neanderthals (a separate but related species, which recent studies indicate survived until about twenty four thousand years ago in the more remote parts of south western Europe [the last traces of Mousterian culture, a type of stone tools primarily associated with Neanderthals, were found in Gorham’s Cave, a natural sea cave located on Gibraltar's east face]). Another migration took place approximately twenty thousand years ago, when Central Asians moved into Siberia before crossing the Bering Sea and populating the Americas. [2]   

For millennia early humans practiced what is called hunter-gathering, but around ten thousand years ago an important change began to take place, our ancestors started to domesticate plants and animals thus providing themselves with a readily available food source, something hitherto unknown, the new security this afforded allowing for a settled lifestyle and eventually the growth of small communities.

Mesopotamia around seven thousand years ago, contained many of these early communities which as they prospered and grew became cities with walls, granaries, temples, priests and a ruling elite. Interconnected by a network of roads and protected by a strong military this land located between the Euphrates and Tigris was the first to achieve that which we now call civilization.

Other civilizations were to follow, the Nile Valley, the Yellow River Valley, Crete, the Indus Valley and various Mesoamerican societies, all arising in areas conducive to growth and all with certain similar features in common, excess food, storage facilities, the protection afforded by walls and a strong military, a priesthood, a ruling elite, laws, roads and a viable trading network to encourage economic growth and stability.

The period between the birth of civilization and the present has been one of highs and lows, a time of religious, social and political upheaval, great plagues and the rise and fall of empires. Mankind has accomplished great things and committed great atrocities. Two world wars were fought with weapons capable of incredible carnage as democracies struggled for survival against totalitarian regimes capable of almost unimaginable evil. While today differing ideologies, religions and political systems along with a struggle to control the Earth's rapidly diminishing natural resources still embroil us in confrontations that have the doomsday clock set at a few minutes to midnight.
 
The Industrial Revolution that began in Britain in the late 18th and early 19th centuries changed the world and was instrumental in creating a middle class with a standard of living undreamed of just a few centuries earlier, unfortunately this revolution, by virtue of its very nature, also sowed the seeds of problems that might yet overwhelm us.

The innovative technologies that have produced the Internet, computers, cell phones, satellites and new modes of transportation encompassing, land, sea, air and space have made the inconvenience created by geography a thing of the past; almost instant communication with anywhere on the planet is an accepted reality and travel is fast, comfortable and affordable.

On October 4, 1957, the Soviet Union ushered in the space age with the launch into orbit of Sputnik 1, Earth's first artificial satellite. This was followed by Sputnik 2 and the first animal sent into orbit, a dog named Laika. The first man to orbit the Earth was Russian Yuri Gagarin on April 12, 1961, followed by American John Glenn on February 20, 1962.

Skylab an American space station was launched on May 14, 1973, and was occupied a total of 171 days by three missions before crashing back to Earth when plans to lift it to a higher orbit failed to materialize.

In 1986 Mir became the first permanent space station; staffed continuously it proved invaluable to the Russian space program, operational in low Earth orbit from 1986 to 2001.

The American Space Shuttle, a revolutionary leap ahead for America’s space program, was a manned partially reusable space vehicle designed to carry large payloads into low Earth orbit safely and cheaply, but there were problems and two were destroyed one on launch in 1986 and a second on re-entry in 2003. In spite of these tragedies the shuttle proved invaluable to the American space effort; it was the launch vehicle for the Hubble Space Telescope, placing it into a 380 mile (612 kilometer) orbit on April 24, 1990, and even with continuing difficulties was instrumental (along with that infamously cramped but dependable workhorse the Russian Soyuz) [3] in the construction and resupply of the International Space Station. In 2011 the shuttles showing their age were finaly retired [4] to be replaced (possibly) by Orion a new generation spacecraft presently under development by Lockhead Martin (the Russians having temporarily assumed the job of space station resupply [subject to a possible re-evaluation following the August 24, 2011, crash of a Progress M-12M unmanned cargo ship the ramifications of which are still undetermined]).

The International Space Station (ISS) originally conceived of as a solely American endeavor (Space Station Freedom) has since become a joint venture of the international space community, an increasing number of space agencies becoming involved both directly and indirectly. First boarded on November 2, 2000, it has been continuously inhabited ever since, staffed by astronauts and cosmonauts of many countries and visited by a few very rich tourists. At present though still under construction it is already functioning in a limited capacity and when completed in 2012 is intended to aid in the human exploration of space, to provide a laboratory for research of all types and to make available a base from which private enterprise can begin to participate in what till now (with the exception of the commercial satellite industry) has been largely a governmental undertaking.

The need for governments to initially lay the groundwork for man’s immergence into space is obvious, but governments are notoriously inefficient, costly and prone to bureaucratic boondoggles. It is now time for private enterprise to get involved in a major way.

The ten million dollar Ansari X Prize (formerly the X Prize) was won in 2004 by Burt Rutan’s SpaceShipOne after it reached space twice within a two week period; Mike Melvill piloted the first flight while Brian Binnie was at the controls for the second. The contest hearkening back to an earlier time when competitions were used to stimulate commercial aviation [5] was sponsored by the non-profit X PRIZE Foundation and was intended to spur civilian spaceflight and promote the development of low cost efficient spacecraft for space tourism. Entrepreneurs are rising to the challenge.

Excited with the success of SpaceShipOne Richard Branson entered into partnership with Burt Rutan, the Spaceship Company the result, a joint venture of billionaire Branson’s Virgin Group and Rutan’s Scaled Composites (acquired by Northrop Grumman August 2007), its purpose to develop and manufacture spacecraft.

Five SpaceShipTwos (a larger and improved version of SpaceShipOne) and to take them to altitude two WhiteKnightTwo motherships (a larger and improved version of WhiteKnightOne) were ordered by Branson's spaceline Virgin Galactic. The first completed mothership named "Eve" was unveiled in front of thrilled onlookers on July 28, 2008, the twin-fuselage carrier aircraft safely making its maiden flight on December 21, 2008, while the first spaceliner (SpaceShipTwo) debuted December 7, 2009, (only slightly behind schedule despite a tragic accident on July 26, 2007, that claimed the lives of three workers and seriously injured three others). The craft (christened the VSS Enterprise) finally taking to the air March 22, 2010, soared majestically high above the Mojave Desert, safe in Eve's embrace, during an almost three hour test flight aimed at checking the rocket plane's aerodynamics in a controlled real-world environment. And then on October 10, 2010, a defining moment, a clean release from Eve and free flight from 45,00 feet (13,700 meters). The eleven minute glide, to a near perfect landing at Mojave Air and Space Port, California, used by pilot Pete Sieblod and co-pilot Mike Alsbury to evaluate handling, lift, drag and stall characteristics and to compare stability and control with computer model predictions.

Spaceport America (the USA’s first built from the ground up commercial spaceport) is one of two new spaceports (the other being Spaceport Sweden) that will be home to the spaceline. A deal has been struck between New Mexico and Virgin Galactic to make the facility situated near Upham, a small town in the southern part of the state, the location where Virgin Galactic headquarters and Mission Control are to be situated.

On Friday October 22, 2010, a double header, a dedication ceremony commemorating completion of the two-mile (3.2 km) long, 200-foot (60 meter) wide main spaceport runway coupled with a flypass and landing of the VSS Enterprise in tandem with its mothership Eve.

The next important step (for Enterprise) piloted rocket tests and then "space."

The first commercial launches involving human passengers are to hopefully begin sometime in 2011/2012 with the first tourists paying $200,000 per trip into space a figure expected to decrease within a few years as technology improves and flights become more routine. Famous personages that have either expressed an interest or already purchased a ticket include Victoria Principal, Dave Navarro and Stephen Hawking; William Shatner when offered a free inaugural ride on the VSS Enterprise declined, stating he did want to go up but needed assurances he would come back, while, for his part, Patrick Stewart allegedly has serious doubts about boldly going where few have gone before.

On August 10, 2011, Virgin Galactic, its future mainstay ostensibly sub-orbital space tourism, was along with six other companies awarded contracts by NASA to provide access to space to researchers and their experiments, a development viewed by Virgin Galactic as both a future mission segment and a significant business opportunity.

The National Aeronautics and Space Administration (NASA) has inked deals and agreements with a number of new spacecraft development companies, in some cases financial support is involved in others they have agreed to share information. This is not some magnanimous or selfless act on the part of the space agency, it's rather an admission that the private sector can service the needs of low Earth orbit a great deal cheaper and more efficiently than they can.

Two companies, Space Exploration Technologies (SpaceX) and Rocketplane Kistler originally shared $500 million in funding, awarded by NASA under the COTS demonstration program, an award intended to help private industry “develop and demonstrate the vehicles, systems and operations needed to resupply, return cargo from and transport crew to a human space facility” in other words the International Space Station or some future government/commercial space habitat.

SpaceX, with its Falcon 9 launch vehicle and Dragon spaceship, is to carry out three flight demonstrations scheduled to take place between 2008 and 2010; the final demonstration will be expected to safely deliver cargo to the ISS and return cargo to Earth. SpaceX was founded by Elon Musk co-founder of PayPal and is based in Hawthorne, California, with launch facilities on Kwajalien Atoll in the Marshall Islands, Cape Canaveral, Florida and at Vanderburg Air Force Station.

There have been problems, however, a third attempt on August 2, 2008, by a Falcon 1 rocket to place a payload into orbit, resulted in failure (the first two also failed), possibly placing SpaceX's ability to compete for future NASA contracts in jeopardy. Three satellites and the ashes of over two hundred people including James Doohan "Scotty" from Star Trek and Mercury astronaut Gordan Cooper were lost.

On the positive side, the first stage and its new Merlin 1C engine destined to power the Falcon 9 worked perfectly.

Rocketplane Kistler utilizing its K1 fully reusable two stage aerospace vehicle had to fulfill similar requirements, including docking and delivering cargo to the space station and returning to Earth. Unfortunately RpK failed to raise 500 million dollars in private financing (a necessary prerequisite for continuance under a renegotiated COTS agreement) and in October 2007, NASA announced that it had terminated funding to the company.

On June 15th, 2010, Rocketplane Inc., its subsidieries and its CEO, George French, filed for chapter 7 bankruptcy.

A number of other companies have signed space commercialization contracts with the space agency and are to receive information concerning projected requirements but little or no funding:  

PlanetSpace is a privately funded Chicago based company founded in 2005, its self proclaimed mission to make space travel available to the general public.

In order to fulfill its mandate the company focused its efforts on two main projects, the Canadian Arrow a 16.5 meter (54.13 foot) two stage rocket presently in development and the Silver Dart a proposed orbital spacecraft/ hypersonic glider which would launch atop a Nova rocket (basically 10 Canadian Arrow rocket engines clustered together) then return to earth in much the same manner as the Space Shuttle.

On November 21, 2007, the Silver Dart initialy intended to be the vehicle that would fulfill NASA's requirements "vis-a-vis," crew and cargo flights to the International Space Station was placed on hold, PlanetSpace announcing its COTS proposal would instead use a spacecraft provided by Lockheed Martin.

Transformational Space Corp (t/Space) has already been involved with NASA; in 2004 it was awarded a $3 million contract to conduct preliminary concept studies for the Crew Exploration Vehicle (Orion) and human exploration of the Moon. This time unlike the winners of the Commercial Orbital Transportation System competition, t/Space will receive only information and technical assistance. The company plans to use a crew transfer vehicle (CXV) that incorporates already proven technology and capsule design. The CXV carrying crew and cargo would be launched on an upscaled version of AirLaunch's QuickReach rocket at present being developed for the DARPA (Defense Advanced Research Projects Agency) FALCON program. The rocket will be dropped from a carrier aircraft (possibly a customized White Knight Two or a modified Boeing 747) and after completing its mission the capsule will return by way of parachute and a water landing.

Blue Origin, bankrolled by Jeff Bezos founder of Amazon, seems to be pushing the envelope with an approach radically different to its competitors, its spacecraft capable of vertical takeoff and landing. Called New Shepard it’s based on the Delta Clipper (DC-X) and Delta Clipper Experimental Advanced (DC-XA), a Department of Defense/NASA effort from the nineties that achieved an impressive turnaround between its second and third flights. Following its fourth flight the DC-XA suffered a landing strut failure due to an unconnected hydraulic line, tipped over then caught fire. The program was ended due to lack of funding.

Blue Origin is presently headquartered in the Seattle, Washington suburb of Kent and has a testing and research center on Corn Ranch, Culbertson County, Texas.

A prototype of New Shepard called Goddard flew successfully on November 13, 2006, followed by two more succesfull flights in March and April 2007. A second test vehicle is purportedly under construction to be followed by a third. Commercial operations are slated to begin as early as 2011.

Blue Origin has been awarded 3.7 million US by NASA under its Commercial Crew Development (CCDev) program to aid in development of the companies "pusher" launch abort system and its lightweight composite pressure vessel.

On Tuesday, December 23, 2008, after careful consideration, NASA awarded two contracts to resupply the International Space Station following the retirement of the U.S. space shuttle fleet. The contracts worth 3.5 billion US were divided between relative newcomer SpaceX, a California company originally based in El Segundo and now located in Hawthorne and Orbital Sciences Corporation (OSC) out of Dulles, Virginia, an established space contractor founded in 1982 and heavily involved in both the aerospace and defence industries.

At 2:45 p.m. EDT (1845 GMT) Friday, June 4, 2010, Space Exploration Technologies (SpaceX) using a Falcon 9 rocket became the first privately funded institution to successfully launch and place into orbit a privately developed space vehicle (albeit a stripped down version of the real thing, called a Dragon Spacecraft Qualification Unit).

On Wednesday, December 8, 2010, Space Exploration Technologies (SpaceX) became the first private company to not only place into orbit but also return to Earth a privately developed space vehicle (this time fully functional). The Dragon spacecraft blasted off at 10:43 a.m. EST (15:43 GMT) from Cape Canaveral Air Force Station, Florida, atop a Falcon 9 rocket into low Earth orbit, performed an intricate set of maneuvers designed to mimic a rendezvous with the "ISS" then returned to Earth and a perfect splashdown some five hundred miles west of Baja, California.

CEO and founder Elon Musk stated that based on the results of the test flight (the flight was the first of three financed by NASA under the COTS program) he planned to ask NASA for permission to combine elements of the second and third missions and send the next Dragon directly to the International Space Station.

NASA agreed; the next Dragon mission will dock with the ISS.

On April 18, 2011, NASA announced a second round of funding under the Commercial Crew Development (CCDev) program. The contracts worth 263.3 million US were divided amongst Boeing, Space Exploration Technologies (SpaceX), Sierra Nevada Corporation and Blue Origin.

As humanity moves outward into space both governments (China plans to have its own space station in orbit by 2022 and a man on the moon by 2024-2030) and private enterprise have a role to play. NASA with the more routine aspects of orbital resupply being assumed by private enterprise can concentrate its efforts on things more in keeping with its expanding mandate, deep space exploration, the search for and mapping of NEOs and the development of suitable shielding necessary to protect deep space astronauts from genetic damage inflicted by cosmic rays and solar radiation. Outer space is the new frontier, space hotels in orbit (Bigelow Aerospace), zero-g laboratories, domed colonies on Mars and solar powered factories located at Lagrangian points processing materials mined on the Moon. The possibilities are almost endless limited only by the vision and imagination of those that dare to dream.

Stephen Hawking, professor at Cambridge University, theoretical physicist and best selling author with his book "A Brief History of Time" has issued provocative statements many times throughout his career: "I don’t think the human race will survive the next thousand years unless we spread into space. There are too many accidents that can befall life on a single planet. But I'm an optimist. We will reach out to the stars." Or "We won’t find anywhere as nice as Earth unless we go to another star system." And "It is important for the human race to spread out into space for the survival of the species; life on Earth is at the ever-increasing risk of being wiped out by a disaster, such as sudden global warming, nuclear war, a genetically engineered virus or other dangers we have not yet thought of."

Heady words to be sure, but just how valid are they? As another great author H.G.Wells speculates in his 1933 book of future history, what is "the shape of things to come?"

The Solar System is located in the Orion Arm of the Milky Way galaxy at a distance far removed from the supermassive black hole at the Galactic center, a region that scientists call the galactic habitable zone, a spherical shell of lessened radiation defined as relatively calm, safe and favorable to the formation of life, where supernova are less frequent and heavier elements more prevalent. The Earth is situated within the Solar System in what is called the circumstellar habitable zone, a spherical shell surrounding the Sun where liquid water can exist on a planets surface and where objects such as comets and asteroids are found less frequently than in more distant regions such as the asteroid and Kuiper belts.

So if the question is does that make us safe? The answer is no, safer perhaps but not safe:

If a supernova was to occur within 200 light years of Earth the cosmic radiation produced could seriously damage the Earth's ozone layer allowing increased ultraviolet radiation to reach the surface (a possible cause of some previous extinctions) and affect susceptible species while within 50 light years it would almost certainly mean the end of all life. Sirius B, a massive white dwarf, orbiting the main sequence star Sirius A (colloquially known as the "Dog Star") and at at a distance of only 8.6 light years one of Earth's nearest neighbors is a possible (though not probable) candidate whereas IK Pegasi B (150 light years) is a white dwarf just shy of the Chandrasekhar limit in orbit about the main sequence star (IK Pegasi A) which is in the end stages of its evolution and poised to become a red giant. When this occurs accretion will push IK Pegasi B past the limit of 1.44 solar masses initiating a Type Ia supernova. Hopefully these events will not happen for millions of years.

A more likely harbinger of catastrophic change would be an asteroid of significant size impacting the Earth. An asteroid striking the Yucatan peninsula caused the Cretaceous-Tertiary extinction event sixty five million years ago and ended the age of the dinosaurs. The Arizona Meteor Crater also known as the Barringer Meteorite Crater was created fifty thousand years ago by an asteroid only fifty meters across, all life out to four kilometers from the blast would have been killed instantly, while the shock wave would have flattened everything up to twenty kilometers away. The Tunguska event of 1908 was probably an asteroid or comet exploding at a height of between five and ten km. If it had happened over a large metropolis such as London, instead of Siberia, it would have wiped out the city with substantial loss of life, hundreds of thousand if not millions dead.

Future asteroid impacts are inevitable because believe it or not near Earth misses are a common occurrence: An asteroid 1994 XM1 passed by Earth at a distance of only 105,000 km (65,000 miles) on December 9, 1994. Asteroid 2002 EM7, approximately seventy meters long, just missed us on March 8, 2002. On August 18, 2002, asteroid 2002 NY40 a five hundred meter (0.3 mile) behemoth approached to within one point three times the Earth-Moon distance. On July 3, 2006, asteroid 2004 XP14, a whopping four fifths of a kilometer wide, passed by at a distance only one point one that of the Moon and asteroid 2007 TU24, 250 meters in diameter, rushed past Earth on January 29, 2008, at a distance only 1.4 times the Moon's orbit. Our latest significant near miss, asteroid YU55, a four hundred meter biggie (about the size of a cruise ship) zoomed between the Earth and Moon at a speed of 30,000 miles per hour November 8, 2011.

As for upcoming events 99942 Apophis with an estimated diameter of 350 meters (1,150 feet) will pass Earth within the orbits of geosynchronous communication satellites on Friday, April 13, 2029, (now that's close) to return April 13, 2036. At present odds of an 2036 impact are considered to be 1 in 250,000. [6]

In the event that the unimaginable were to become reality how prepared are we?

Well at the moment not very, but there is a glimmer of light on the horizon, initiatives are currently being advanced by the "Association of Space Explorers" an international organization composed of astronauts and cosmonauts who believe it is imperative to develop a plan which will facilitate a global response in the event an asteroid is discovered on a collision course with Earth.

By reply, a group of scientists, engineers and other professionals have been tasked to come up with possible recommendations by both individual governments and the United Nations. [7]

In conjunction, recognizing that the further away a threat is detected, the more time there is to affect a solution has prompted the United States Congress to ask NASA to be more aggressive in its tracking of Near-Earth Objects (NEOs). The new mandate may include the building of innovative detection systems or investment in systems already under development such as Pan-Starrs or the Large Synoptic Survey Telescope.

If annihilation from space isn’t enough home grown events also threaten our existence:

Present day global warming possibly caused by a runaway greenhouse effect [8] [9] is becoming a matter of grave concern as storms increase in intensity and some species face extinction.

In the Southern Hemisphere the Antarctic ice sheets are becoming increasingly stressed by temperatures that have risen (in some regions) 2.5 degrees Celsius in the last 50 years: Larsen B, one of numerous coastal ice shelves (floating extensions of the ice sheets) broke free in 2002. The 12,000 year old ice mass had a surface area of  3,250 kilometers, bigger than the state of Rhode Island. Larsen A, considerably smaller broke off in 1995 and Larson C, much larger could quite possibly follow suit in the near future. Other shelves have also broken free and glaciers such as Pine Island and Thwaites are shrinking. If the melting trend continues many scientists believe that the southern continent could become a significant contributor to rising sea levels. [10]

In the Northern Hemisphere things appear to be even worse; Arctic ice is melting at an ever increasing rate and as with elsewhere appears caught in a feedback loop. The more the ice melts the less reflectivity and less reflectivity means increased melting. The latest data (though controversial) indicates that summer sea ice will have almost vanished within forty years. The North Pole will be open water, the Northwest Passage a reality, the frigid world of explorers such as Frobisher, Hudson and Perry a distant memory.

If you’re worried that the runaway greenhouse effect will turn Earth into another Venus don’t be; Mother Nature has a solution, one that she has applied numerous times in the past. Recent ice cores taken from Greenland’s ice sheet reveal that Earth's climate has undergone many abrupt transformations, changes that are directly linked to massive amounts of fresh melt water pouring into the North Atlantic Ocean and a consequent shutting down of the heat pump known as the Gulf Stream. The loss of this moderating influence, would in a period of only two or three years cause atmospheric temperatures to plunge drastically. The worst-case scenario, a full blown ice age, secondary scenario, a mini ice age and subsequent disruption of worldwide weather patterns, extremely long bitter winters, crop failures and either flooding or drought depending on location.

The ozone layer is located in a region of the Earth’s atmosphere called the stratosphere. The gas is extremely tenuous with concentrations of only a few parts per million and is created when ultraviolet light strikes oxygen molecules and begins a process called the ozone-oxygen cycle. Although the amount of ozone as a percentage of the atmosphere is very small it plays a role of vital importance, absorbing dangerous ultraviolet radiation, which if allowed to reach the surface unfiltered can lead to increases in skin cancer, serious genetic damage to living organisms both plant and animal and possibly the extinction of vulnerable life forms.

Ozone depletion due to the introduction of man made organohalogen compounds such as chlorofluorocarbons (CFCs) has been ongoing for a long time, ozone levels dropping as much as four percent a decade. Even greater seasonal declines over the North and South Poles have resulted in the appearance of what are called ozone holes.

The hole over the North Pole is relatively small, it is the hole over the South Pole that is the most disconcerting; discovered in 1985 by Farman, Gardiner and Shanklin then confirmed by satellite the huge hole stunned the scientific community. World wide measurements by surface based Dobson spectrophotometers confirmed the worst, that the ozone layer was in a state of depletion everywhere except the tropics. Recognizing the seriousness of the findings an international treaty called the Montreal Protocol was signed by the major offending nations. CFCs, halons and other related substances were phased out and eventually banned in 1996.

The ozone layer is expected to recover significantly over the coming century due to the ban on ozone-depleting substances, and the Antarctic hole despite reaching a size of 29 million square km on September 24, 2006, (large enough to cover parts of Australia and New Zealand) will hopefully revert to pre-1980 levels by the year 2075.

Terrorism and the proliferation of nuclear weapons are twins linked by insanity their promise Armageddon and the end of humanity:

The short period during which atomic weapons were confined to the arsenals of a few relatively stable countries, the so-called nuclear club, Great Britain, France, the United States, India et al. appears to be over, for like a malignant tumor the club is growing and its newest member North Korea is neither stable nor rational while Iran, a country regarded by many to be a major sponsor of world terrorism, is knocking at the door ready to join.

Worrisome developments? Yes:

As more and more countries acquire nuclear weapons, the possibility of nuclear war either accidentally or by design increases exponentially the consequences frightening. Add to this the prospect of these weapons falling into the hands of terrorists whose avowed goal is the destruction of the West and the future seems grim indeed. A nuclear strike by one country or group on another would invite immediate retaliation and result in the death of millions, escalation could then plunge us into all out war, the conflagration followed by nuclear winter, the collapse of civilization and the possible end of all life an insane scenario no sane minded individual could possibly want or even truly imagine.

Clearly there are problems, but the great adventure has begun and the stars beckon; it's time to leave our petty squabbles behind and go forward in a spirit of both optimism and co-operation. Our survival as a race may well depend on us spreading throughout the cosmos so that an event no matter how cataclysmic can’t destroy us all, but lets proceed with the right motivation and not like the aliens of science fiction who having devastated their own world are desperately scouring the galaxy in search of another. The future is what we make it, lets hope we make it right.

[1] The designation (habitable) does not mean that all planets within the zone harbor life nor that life can’t exist outside the zone. Mini-habitable zones within a star system may exist in which the sun is not the primary factor determining a planetary bodies ability to sustain life e.g., Europa, one of the moons of Jupiter, constantly stressed (heated) by gravitational interaction with its giant primary.
 
[2] In what can only be considered a surprising addition to the saga of human expansion, recent mitochondrial DNA gathered from amongst the indigenous peoples of North America (the Ichigua tribe have an extremely high incidence of pre-Columbian European DNA) and hard evidence such as a Solutrean bifaced (two-sided) flint point (the neolithic Solutreans of southwest France/northwest Spain, were amongst the first peoples to increase a flints strength using heat, their toolmaking characterized by bifacial, percussion and pressure-flaked points) found at Cactus Hill, Virginia, which is similar but predates the 12,000 year old Clovis points of New Mexico by thousands of years, offers the possibility that small migrations of ice age Europeans (perhaps, as Dennis Stanford [head of archaeology at the Smithsonian] has suggested, utilizing a combination of animal hide boats and an ice bridge which connected North America with Europe) established themselves in the Americas millennia before a land bridge from Asia to Alaska opened up allowing a much larger migration from Siberia. It also appears that upon contact those of European descent (the skeleton of what is known as Kennewick Man complete with a Cascade point lodged in its pelvis was found in Washington state, is approximately 9,300 yrs old and has a skull with features [albeit controversial] characteristic of modern day Caucasoid peoples) were either eliminated or as the genetic markers indicate, assimilated.

[3] A Soyuz capsule is docked with the International Space Station at all times to be used as an escape craft in the event of emergency.

[4] After 30 years of service NASA's space shuttle fleet is no more, Atlantis, last of its kind, landed in the pre-dawn hours Thursday, July 21, 2011, at Kennedy Space Center, Cape Canaveral, Florida, following a final resupply mission to the International Space Station,

[5] The twenty-five thousand dollar Orteig Prize offered by hotel owner Raymond Orteig was won by Charles Lindbergh in 1927, when he became the first aviator to fly solo non-stop from New York to Paris in his single engine plane the Spirit of St. Louis.

[6] If Apophis were to impact Earth estimates are that the energy released would be in the 510 megaton range which though horrendous would be unlikly to trigger any long lasting global effects (the largest hydrogen bomb explosion was 50 megatons, the Krakatoa erruption was the equivalent of 200 megatons while the dinosaur ending Chicxulub impact was approximately 100,000,000 megatons).

[7] United Nations officials and leaders of various space agencies were briefed on the threat of Near-Earth Objects (NEOs) and the need for a coordinated global response by members of the Association of Space Explorers and other experts on November 25, 2008. The UN having begun discussions on the issue early in 2009 will continue to meet formally on an ongoing basis.

[b] In early 2012 a new consortium of universities, research institutes and high tech companies drawn from the UK, Germany, France, Spain, Russia and the US was established to deal with the threat of asteroids, comets and further space detritus found to be on a collision course with Earth. Named NEOShield the project led by the German Aerospace Center (DLR) and supported by European Commision money will explore the means by which an impact threat can be successfully mitigated. Methods being explored include a kinetic impactor (slamming something heavy into the object), a gravity tractor (the miniscule mass of a spacecraft positioned near the object could theoretically, over time, affect its course) and blast deflection (detonating a nuclear device near, on or under the surface of the object).

[8] The verdict is still out on whether global warming is a cyclical event heavily influenced by solar activity or man-made the result of carbon emissions.

[9] There is a distinct difference between the term greenhouse effect which is a warming of the atmosphere due to naturally occurring greenhouse gases and without which the Earth’s surface would be as much as 30 °C colder and the afore-mentioned runaway greenhouse effect which is a result of gases introduced by humans, stemming in part from the industrial revolution and the subsequent large scale burning of fossil fuels.

[10] Antarctica is more than just coast, however, and the overall picture somewhat more complicated; temperatures in the interior of the vast continent have apparently fallen over the same period the harsh desert valleys noticeably cooler.

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