Radiocarbon dating is a radiometric detection technique used to estimate the age of carbon bearing (Organic) material. The method was developed by Willard Libby in 1949 at the University of Chicago. He received the 1960 Nobel Prize in Chemistry for “his method to use Carbon-14 for age determinations in archaeology, geology, geophysics, and other branches of science.”
There are three isotopes of carbon, C12, C13 and C14. C12 and C13 are stable while C14 is unstable with a half life of 5730 +- 40 years. The concentration of C14 is minuscule 0.0000000001%. Carbon 14 is formed by action of Cosmic rays on the Nitrogen present in the upper atmosphere.
14N7 + n –> 14C + p
Over a period of thousands of years, C14 decays back to 14N by beta decay.
14C –> 14N + b
The concentration of carbon 14 remains comparatively stable over the years. As plants takes in CO2 for photosynthesis, the concentration of C14 in them remains constant. As animals eat and breath, the concentration of C14 in their body remains constant as well. When these plants/animals die, there is no recycling of C14 and over the span of hundreds of years, the C14 decays and the percentage of C14 to C12/C13 goes down. Since the half life of C14 is around 5730 years, the concentration of C14 in a dead animal/plant will be half what it was when the plant/animal died. By calculating the concentration of C14 in a plant/animal sample and comparing it with the normal C14 concentration, we can figure out how old the sample was. Any material containing carbon can thus be dated. After about 10 half lives, the concentration becomes so small that it becomes useless in identifying the age. Thus, radiocarbon dating can be used for dating a sample to a maximum of 50,000 to 60,000 years.
The atmospheric C14 concentration does not remain constant. It varies due to changes in cosmic ray intensity, volcanic activity, variations in Earth’s magnetosphere (which affects cosmic ray intensity). Human activity like the industrial revolution and atmospheric nuclear testing also affects the concentration. The radiocarbon dating process needs to be calibrated to account for these variations. Examination of tree growth rings (concentric growth rings in really old trees can be used to estimate the age of the tree), deep ocean sediment layers, coral samples helps in calibration. Calibration curves can help in more accurate age estimation.
Panspermia is an hypothesis which says that life, at least single cellular ones, are abundant in the universe and that they piggy back on meteors and comets to seed new planets and moons. Panspermia does not tell us how the life was created, but just that the life once created travelled or travels to far reaches of the universe. Meteor impacts on a life bearing planet could eject material containing living organisms into space. These material form the basis of next generation of comets and asteroids and may contain living organism or at least chemicals that could form the basis for life.
Even on planet earth, we have found living organisms in extreme conditions. Certain bacteria can survive deep below the ocean surface under extreme pressure, others are able to survive in extreme cold, acidic or even vacuum environment. Variants of these bacteria could remain dormant on interstellar or interplanetary journey.
The Panspermia hypothesis do suffer from some serious drawbacks. The value of the Drake’s equation using the currently available data comes to around 10 which implies that there could be 10 civilizations in the Milky way with which we can communicate. But the galaxy is immense. Any travel between stars at the kind of speed that comets travels would take millions of years. It is unlikely that any organism, however resilient, would be able to survive that journey. Even if hundred meteors are formed from earth, the probability that any of them would contain organism that could survive the extreme temperatures of space, the vacuum, cosmic radiations, sun’s radiation is very low. That it would be able to escape out of the sun’s gravity and that of the gas giants gravity is even low. That it would be pointed at the correct planet, that could sustain life, of the correct star (Not too big and not too small) is infinitesimal. That it would survive the long journey reduces that probability even further (Half life of DNA is 1.1 Ma). Even after this the chances of the organisms to survive the crushing impact with the planet makes this probability even lower than infinitesimal. Absence of a thriving microcosm on Venus or Mars, which have environment similar to the early years of earth, indicates that Panspermia is unlikely. Organism that could have survived the arduous journey to these planets would have thrived there.
It is possible that life was seeded on planet earth by some extraterrestrial civilization (God?) and that we are or will in future seed life on other planet. Although, the space agencies do take extreme precautions to avoid contaminations, space crafts sent by us to other planets can contain microorganisms that can eventually lead to life on those planets. Directed Panspermia hypothesis states that an advanced civilization can create thousands, may be millions of meteor based space crafts, powered by solar sails and point them towards regions of the galaxy where new stars and planets are being formed. A little nudging by the onboard computer could take these meteor crafts to the correct stars and the correct planets to seed them. For a sufficiently advanced civilization that has spread to an entire star system, this would be comparatively trivial to achieve.
May be someday, buried deep below the earth’s crust, we will find a meteor with the remnants of the first life and the first computer on earth.