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le of genetic material passed from one living entity toanother； and has never stopped moving since。 it was the moment of creation for us all。
biologists sometimes call it the big birth。
鈥渨herever you go in the world； whatever animal； plant； bug； or blob you look at； if it isalive； it will use the same dictionary and know the same code。 all life is one；鈥潯ays mattridley。 we are all the result of a single genetic trick handed down from generation togeneration nearly four billion years； to such an extent that you can take a fragment of humangenetic instruction； patch it into a faulty yeast cell； and the yeast cell will put it to work as if itwere its own。 in a very real sense； it is its own。
the dawn of life鈥攐r something very like it鈥攕its on a shelf in the office of a friendlyisotope geochemist named victoria bennett in the earth sciences building of the australiannational university in canberra。 an american； ms。 bennett came to the anu fromcalifornia on a two…year contract in 1989 and has been there ever since。 when i visited her； inlate 2001； she handed me a modestly hefty hunk of rock posed of thin alternating stripesof white quartz and a gray…green material called clinopyroxene。 the rock came from akiliaisland in greenland； where unusually ancient rocks were found in 1997。 the rocks are 3。85billion years old and represent the oldest marine sediments ever found。
鈥渨e can鈥檛 be certain that what you are holding once contained living organisms becauseyou鈥檇 have to pulverize it to find out；鈥潯ennett told me。 鈥渂ut it es from the same depositwhere the oldest life was excavated； so it probably had life in it。鈥潯or would you find actualfossilized microbes； however carefully you searched。 any simple organisms； alas； would havebeen baked away by the processes that turned ocean mud to stone。 instead what we would seeif we crunched up the rock and examined it microscopically would be the chemical residuesthat the organisms left behind鈥攃arbon isotopes and a type of phosphate called apatite； whichtogether provide strong evidence that the rock once contained colonies of living things。 鈥渨ecan only guess what the organism might have looked like；鈥潯ennett said。 鈥渋t was probablyabout as basic as life can get鈥攂ut it was life nonetheless。 it lived。 it propagated。鈥�
and eventually it led to us。
if you are into very old rocks； and bennett indubitably is； the anu has long been a primeplace to be。 this is largely thanks to the ingenuity of a man named bill pston； who isnow retired but in the 1970s built the world鈥檚 first sensitive high resolution ion microprobe鈥攐r shrimp； as it is more affectionately known from its initial letters。 this is amachine that measures the decay rate of uranium in tiny minerals called zircons。 zirconsappear in most rocks apart from basalts and are extremely durable； surviving every naturalprocess but subduction。 most of the earth鈥檚 crust has been slipped back into the oven at somepoint； but just occasionally鈥攊n western australia and greenland； for example鈥攇eologistshave found outcrops of rocks that have remained always at the surface。 pston鈥檚 machineallowed such rocks to be dated with unparalleled precision。 the prototype shrimp was built and machined in the earth science department鈥檚 own workshops； and looked like somethingthat had been built from spare parts on a budget； but it worked great。 on its first formal test； in1982； it dated the oldest thing ever found鈥攁 4。3…billion…year…old rock from westernaustralia。
鈥渋t caused quite a stir at the time；鈥潯ennett told me； 鈥渢o find something so important soquickly with brand…new technology。鈥�
she took me down the hall to see the current model； shrimp ii。 it was a big heavy pieceof stainless…steel apparatus； perhaps twelve feet long and five feet high； and as solidly built asa deep…sea probe。 at a console in front of it； keeping an eye on ever…changing strings offigures on a screen； was a man named bob from canterbury university in new zealand。 hehad been there since 4 a。m。； he told me。 shrimp ii runs twenty…four hours a day； there鈥檚 thatmany rocks to date。 it was just after 9a。m。 and bob had the machine till noon。 ask a pair ofgeochemists how something like this works； and they will start talking about isotopicabundances and ionization levels with an enthusiasm that is more endearing than fathomable。
the upshot of it； however； was that the machine； by bombarding a sample of rock withstreams of charged atoms； is able to detect subtle differences in the amounts of lead anduranium in the zircon samples； by which means the age of rocks can be accurately adduced。
bob told me that it takes about seventeen minutes to read one zircon and it is necessary toread dozens from each rock to make the data reliable。 in practice； the process seemed toinvolve about the same level of scattered activity； and about as much stimulation； as a trip to alaundromat。 bob seemed very happy； however； but then people from new zealand verygenerally do。
the earth sciences pound was an odd bination of things鈥攑art offices； part labs；part machine shed。 鈥渨e used to build everything here；鈥潯ennett said。 鈥渨e even had our ownglassblower； but he鈥檚 retired。 but we still have two full…time rock crushers。鈥潯he caught mylook of mild surprise。 鈥渨e get through a lot of rocks。 and they have to be very carefullyprepared。 you have to make sure there is no contamination from previous samples鈥攏o dustor anything。 it鈥檚 quite a meticulous process。鈥潯he showed me the rock…crushing machines；which were indeed pristine； though the rock crushers had apparently gone for coffee。 besidethe machines were large boxes containing rocks of all shapes and sizes。 they do indeed getthrough a lot of rocks at the anu。
back in bennett鈥檚 office after our tour； i noticed hanging on her wall a poster giving anartist鈥檚 colorfully imaginative interpretation of earth as it might have looked 3。5 billion yearsago； just when life was getting going； in the ancient period known to earth science as thearchaean。 the poster showed an alien landscape of huge； very active volcanoes； and asteamy； copper…colored sea beneath a harsh red sky。 stromatolites； a kind of bacterial rock；filled the shallows in the foreground。 it didn鈥檛 look like a very promising place to create andnurture life。 i asked her if the painting was accurate。
鈥渨ell； one school of thought says it was actually cool then because the sun was muchweaker。鈥潯。╥ later learned that biologists； when they are feeling jocose； refer to this as the鈥渃hinese restaurant problem鈥濃�攂ecause we had a dim sun。） 鈥渨ithout an atmosphereultraviolet rays from the sun； even from a weak sun； would have tended to break apart anyincipient bonds made by molecules。 and yet right there鈥濃�攕he tapped the stromatolites鈥斺�測ouhave organisms almost at the surface。 it鈥檚 a puzzle。鈥�
鈥渟o we don鈥檛 know what the world was like back then？鈥�
鈥渕mmm；鈥潯he agreed thoughtfully。
鈥渆ither way it doesn鈥檛 seem very conducive to life。鈥�
she nodded amiably。 鈥渂ut there must have been something that suited life。 otherwise wewouldn鈥檛 be here。鈥�
it certainly wouldn鈥檛 have suited us。 if you were to step from a time machine into thatancient archaean world； you would very swiftly scamper back inside； for there was no moreoxygen to breathe on earth back then than there is on mars today。 it was also full of noxiousvapors from hydrochloric and sulfuric acids powerful enough to eat through clothing andblister skin。 nor would it have provided the clean and glowing vistas depicted in the poster invictoria bennett鈥檚 office。 the chemical stew that was the atmosphere then would haveallowed little sunlight to reach the earth鈥檚 surface。 what little you could see would beillumined only briefly by bright and frequent lightning flashes。 in short； it was earth； but anearth we wouldn鈥檛 recognize as our own。
anniversaries were few and far between in the archaean world。 for two billion yearsbacterial organisms were the only forms of life。 they lived； they reproduced； they swarmed；but they didn鈥檛 show any particular inclination to move on to another； more challenging levelof existence。 at some point in the f