OLD, GOLD AND GOR­GEOUS

Plants and an­i­mals trapped in am­ber cre­ate a minute in time that is pre­served for tens of mil­lions of years. PAUL WIL­LIS reports.

Cosmos - - Contents -

Fos­sils in am­ber show life 99 mil­lion years ago, writes PAUL WIL­LIS.

IN GREEK MYTHOL­OGY, they were thought to be the tears of the sisters of Phaë­ton, son of He­lios, the Sun God. They were in­cluded in jew­ellery as far back as the Ne­olithic pe­riod. They first ap­pear in the lit­er­a­ture in the fourth cen­tury BCE in the writ­ings of Theophras­tus and, later, Pyth­eas. Their honey- gold trans­par­ent al­lure has trans­fixed peo­ple for thou­sands of years. And now am­ber, and its oc­ca­sional cargo of fos­sil in­clu­sions, is retelling the story of life in ex­quis­ite de­tail.

The ori­gin of am­ber is much more pro­saic than the tears of the gods. It started out as drib­bles of plant sap, per­haps fallen to the for­est floor in sticky blobs. Once buried in sed­i­ment, the sap un­der­goes molec­u­lar poly­meri­sa­tion,

hard­en­ing un­der heat and pres­sure to form, first, an in­ter­me­di­ate sub­stance known as co­pal, and then am­ber it­self. But it’s while still freshly ex­uded and vis­cous that it some­times en­snares a hap­less passing crea­ture, trap­ping it for­ever.

The old­est am­ber dates back 320 mil­lion years to the Up­per Car­bonif­er­ous pe­riod. There are hun­dreds of lo­cal­i­ties all over the world that pro­duce th­ese glassy­golden stones, but only a few pro­duce spec­i­mens with fos­sils trapped within.

The largest de­posit of am­ber comes from the Baltic re­gion, which cov­ers eastern Ger­many, Poland and Rus­sia. Re­cent anal­y­sis shows that the orig­i­nal resin came from a rare group of conifer trees, of which there is only one species alive today – the Ja­panese Um­brella pine ( Sci­ado­pi­tys ver­ti­cil­latei). Al­though re­cov­ered from ma­rine sands dated as 25 mil­lion years old, anal­y­sis of the in­sects oc­ca­sion­ally found in Baltic am­ber re­veals that it is con­sid­er­ably older still, dat­ing from be­tween 44 and 49 mil­lion years ago.

The Do­mini­can Repub­lic in the Caribbean is renowned for pro­duc­ing yel­low, gold and rare blue am­ber of ex­cep­tional clar­ity. It also pro­duces more fos­sils, par­tic­u­larly of in­sects, than the Baltic va­ri­ety. Dat­ing to around 25 mil­lion years ago, the en­vi­ron­ment in which the sap was pro­duced was a trop­i­cal for­est filled with lianas, shrubs and large trees. The sap it­self can be traced back to the now- ex­tinct species of tree, called Hy­menaea pro­tera, from a genus that can still be found grow­ing in the trop­i­cal Amer­i­cas and the east coast of Africa today.

But most of the spec­tac­u­lar fos­sils re­cov­ered over the past decade or so have come from Myan­mar – where al­most a third of spec­i­mens un­earthed con­tain all or part of a once-liv­ing crea­ture. This am­ber has been mined for jew­ellery since the first cen­tury CE. Most of it comes from Hukawng Val­ley in Kachin State in the north of the coun­try. Today there is a large, un­reg­u­lated in­dus­try min­ing Myan­mar am­ber and most of the prized fos­sil spec­i­mens are sold to pri­vate col­lec­tors, of­ten putting them out of reach of sci­en­tific study.

Myan­mar am­ber con­tains a huge va­ri­ety of an­i­mals and plants from a 99-mil­lion-year- old trop­i­cal for­est. This was a time, late in the Age of the Di­nosaurs, where many types of an­i­mals and plants were un­der­go­ing sig­nif­i­cant changes, and we see the first ap­pear­ance of sev­eral groups that are fa­mil­iar to us today.

The beauty of am­ber as a medium for cre­at­ing fos­sils is that it forms a per­fect im­pres­sion of the sur­face of the crea­ture or plant en­tombed within. The body of the an­i­mal de­cays to car­bon that can line the cav­ity cre­ated by the orig­i­nal form. The fidelity of the sur­face im­pres­sion is so high – and the size of many of the crea­tures is so small – that the fos­sils can be scanned and then blown up to re­veal the tini­est de­tails.

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