Spider web in amber
One of the rough and ready ways of separating amber from the many plastic simulants that have been produced over the last century or so is to make a glass of powerfully salty water and drop the samples in. The amber should float, while the plastics will tend to sink, as they have a higher specific gravity (roughly its density compared to that of water, whose reference is taken as 1. Most minerals have a specific gravity somewhere between 2.5 and 3.5 for example). Amber is denser than normal water with tis specific gravity of 1.08, but the added salt raises the water’s density, allowing the amber to float. Thanks to this set of interacting properties amber can travel by sea considerable distances, and on the morning after a storm on the beaches of southern and eastern England you will see beachcombers staring at the ground seeking chunks of the warm golden gem that have floated all the way from their source in the Baltic Sea hundreds of kilometres eastwards. Scientists join in the fun, hoping to discover new inclusions to study, and a serendipitous find on a Sussex beach has turned up the oldest spider web ever found, dated at roughly 140 million years and preserved in the fossilised sap of an early Cretaceous tree.
They sliced the amber into sections and examined them under a microscope, finding many similarities to modern spider webs, including drops of glue designed to trap any insects that contact it. They suggest the find may be evidence of the co-evolution of spiders and flying insects, since the latter experienced a large radiation between 140 and 130 million years back. The appearance of glue drops may represent a response in feeding patterns to a change in equilibrium between different sources of spider food in the Cretaceous ecosystem. Nearly all the preserved spider webs known were preserved in amber, since it is very rare in the mineral fossil record. In this case the researchers suggest a wildfire scarred the trees, causing them to release sap to heal the wounds, imprisoning part of the web of this long gone arachnid. As well as the web, well preserved soil forming bacteria were found in the sample, showing that similar processes to today’s were happening in those now vanished Cretaceous soils.
Loz
Image credit, spider with web in Baltic amber: Mila Zinkova
(Source: facebook.com)
