Living fossil stromatolites found in Northern Ireland

Stromatolites don't look like very much when you actually see them, but they are among the oldest evidence for life on Earth. They are interpreted as layers of sediment aggregated by mats of microbial organisms, which lived in shallow waters receiving lots of sunlight. Although traces of the microorganisms themselves are very rarely preserved, the characteristic cushion-shaped mats remain. Such structures are called "microbialites".

They appear in the fossil record in the late Archaean, about 3.5 billion years ago, and in the Proterozoic, from 2.5 billion years ago, they are believed to have been mostly made by cyanobacteria. The University of California Museum of Paleontology has a great introduction to cyanobacterial fossils and Proterozoic life on its history of life website.

Stromatolites are rare today, and one of the main hypotheses for this is that herbivore grazers would readily attack such a concentrated source of food. The best known examples of modern stromatolites are those in Shark Bay, Western Australia, where they live in highly saline water, which is not conducive to such herbivore grazers.

So it's a surprise to hear that a small stromatolite colony has been found among the rocks of the famous Giant's Causeway in Northern Ireland. The colony is in brackish water that is exposed to waves and potential grazers. It was found by environmental scientists from the University of Ulster who were out looking for other some geological features.

The basaltic columns of the Giant's Causeway, where the stromatolite was found.

The Causeway itself is an extraordinary geological structure, composed of interlocking "pillars" of basalt formed by volcanic activity. These pillars are more or less hexagonal in cross-section, making it look like a set of giant stepping stones.

A little more browsing on Wikipedia throws up a list of other modern stromatolites around the world, some of which are in fresh water. It's amazing how quickly the news report on the new stromatolite find was picked up and incorporated into Wikipedia.

I'm quite a fan of stromatolites. I had the opportunity to see some fossilized stromatolites in the field when my palaeontology class in college went out to upstate New York, to the fossil-rich area around Utica. Unfortunately most fossils look much better in the full glare of the sun (and the excitement of the moment!) than when they are photographed:

Stromatolite fossils in the ground. There's really something there, I swear!

The scientist who found them suggested that they could be much more common than we think they are. It would be really intriguing to see them live in the field, and even more informative to compare the cyanobacteria from different stromatolite colonies around the world: are they always the same kind of bacteria? What else is in these mats? How fast do they grow? What triggers the formation of these microbial mats? How curious, that slimy mats of microbes are the ones to tell us about the early origins of life on our planet!

History of Amazon Basin Shaped by Andes

Here's something that has relevance to the name of this blog. The traditional model for the history of Amazonian biodiversity held that much of it weathered the Pleistocene period in forest fragments, or refugia, and from there spread out again to repopulate the basin when the climate again became amenable. These so-called diversity centers, however, have been shown to be artifacts of sampling, rather than a real biotic phenomenon, pushing back the origins of diversity in the Amazon to earlier periods of geological history.

Amazonia today. From Hoorn et al. 2010 (Link)

A recent review in Science magazine synthesizes what is known about the geological and biological past of the Amazon, to reconstruct a scenario where the uplift of the Andes mountains, which are relatively young, is responsible in part for the present-day patterns of diversity in the basin. Prior to the Andes uplift (which began in the Paleogene after the end-Cretaceous 65 Mya, and continues to the present day), the geology of Amazonia was 'cratonic', i.e. it was dominated by the rocks of the continental center. The rising mountain range changed both the climate, e.g. by intensifying rainfall to the East of the range, and also the landscape, as sediment eroded off the mountain faces and came to be deposited in the basin below. Extensive, inland wetlands (the Pebas system) first appeared in correlation with intensified uplift and then disappeared, replaced by a riverine, fluvial landscape.

The present-day biota of the Amazon is very much terrestrial. Therefore, the disappearance of the extensive wetlands, which formerly fragmented the terrestrial forests, was a prerequisite for the appearance of modern Amazonian fauna and flora. Furthermore, diversity as measured today for both mammals and tree species is highest where the soils are of Andean origin (swept down by erosion and deposited by the rivers), as opposed to where the original cratonic soils remain at the surface. Perhaps the nutrient levels are linked to both forest productivity and resultant diversity, but the climate engendered by the topographic relief may also have a role in patterns of diversity.

This is very much a 'big picture' review, and is worth reading to think about how the literal shape of the Earth has a role in defining the life that dwells as a thin film on its surface.

Anthropocene - an epoch that reflects human impact on Earth's history

The last ~10,000 years of the Earth's history, since the end of the "ice age" is called the Holocene epoch in the geological time scale. Likely proposed by Sir Charles Lyell in 1833, the Holocene was adopted by the International Geological Congress in 1885.

This it includes the period that covers all of human civillisation. Since then, mankind's activities have been so so impactful to the planet's climate and ecosystems as to be geological in nature.

In 2000, Paul Crutzen and Eugene Stoermer suggested that this influence of human behavior on the Earth constituted a new geological era, the "Anthropocene". ["The "Anthropocene"," by Paul J. Crutzen & Eugene F. Stoermer. Global Change Newsletter, 41: 17-18.]

Summarising previous observations of human impact in the literature and examples of the many global impacts, the authors then say,

"Considering these and many other major and still growing impacts of human activities on earth and atmosphere, and at all, including global, scales, it seems to us more than appropriate to emphasize the central role of mankind in geology and ecology by proposing to use the term "anthropocene" for the current geological epoch. The impacts of current human activities will continue over long periods."

They proposed the later part of the 18th century as the starting point, from when global effects become noticeable.

GSA Today just published a paper that makes an argument for its consideration as a formal epoch. The team of British geologists, all members of the Stratigraphy Commission of the Geological Society of London, ask, "Are we now living in the Anthropocene?"

"The term Anthropocene, proposed and increasingly employed to denote the current interval of anthropogenic global environmental change, may be discussed on stratigraphic grounds.

A case can be made for its consideration as a formal epoch in that, since the start of the Industrial Revolution, Earth has endured changes sufficient to leave a global stratigraphic signature distinct from that of the Holocene or of previous Pleistocene interglacial phases, encompassing novel biotic, sedimentary, and geochemical change.

These changes, although likely only in their initial phases, are sufficiently distinct and robustly established for suggestions of a Holocene-Anthropocene boundary in the recent historical past to be geologically reasonable.

The boundary may be defined either via Global Stratigraphic Section and Point ("golden spike") locations or by adopting a numerical date.

Formal adoption of this term in the near future will largely depend on its utility, particularly to earth scientists working on late Holocene successions. This datum, from the perspective of the far future, will most probably approximate a distinctive stratigraphic boundary."

- Zalasiewicza, J, M Williams, A Smith, TL Barry, AL Coe, PR Bown, P Brenchley, D Cantrill, A Gale, P Gibbard, FJ Gregory, MW Hounslow, AC Kerr, P Pearson, R Knox, J Powell, C Waters, J Marshall, M Oates, P Rawson & P Stone, 2008. Are we now living in the Anthropocene. GSA Today, 18 (2): 4-8.