Question of the Week

Where does coal come from?

Over 300 million years, before the dinosaurs, the climate was warm and humid, inhabited with some of the first swamps on Earth. In particular, these swamps were dominated by vast amounts of plants, including tree-sized clubmosses, called scale trees. Some of these trees grew to 130 feet tall, producing vast amounts of bark as well as wood. As these trees died and fell over into the swamp, they didn't fully decompose. Over time, this carbon-rich material was covered over and compressed, slowly becoming brown coal (lignite) and then the anthracite used in coal-burning powerplants. All of that trapped carbon, from photosynthesis 300 million years ago, is now being released into our modern environment... causing global warming.

What is amber?

Amber is tree resin that has been fossilized. These resins are produced by living trees as a defense mechanism against insect and fungal attacks, and sometimes traps other organisms such as tree-dwelling invertebrates. The conditions inwhich the organism are entombed can reveal amazing preservation.

Many trees produce resins, and these products will usually degrade and decompose. Some resins seem to be more resistant to decay, and through high temperatures and pressures, these tree resins turn into copal. With sustained heat and pressure in the sedimentary rock cycle they become amber.

Amber from the Americas and Africa are probably created from ancestors of Hymenaea, a legume tree that grows in the tropical Americas. Amber found in Europe probably formed from resins produced by relatives of the tropical kauri pines, Agathis, which still live in Oceania. Baltic ambers are thought to be fossil resins from relatives of the umbrella pines, Sciadopitys, that once lived in north Europe, but only has one surviving species native to Japan.

The oldest amber is from the early Pennsylvanian, but it's origin is unknown. Amber has been sporadically found throughout the Mesozoic, but most amber finds increase during the Cretaceous and Cenozoic, presumably with the rise of the angiosperms.

Above: Ant trapped in Baltic amber