Humble Ferns – Evidence to support the Impact Theory?

By | November 4th, 2007|Dinosaur and Prehistoric Animal News Stories, Main Page, Palaeontological articles|0 Comments

Fossil Fern Pollen – Evidence to support the Asteroid/Meteorite Theory?

With the recently published paper citing the volcanic activity that caused the Deccan Traps as the main driving force behind the mass extinction that occurred 65 million years ago, it might be time to review some of the other evidence gathered by scientists to help explain what exactly went on.

In Denmark, about 40 kilometres south of the capital city, Copenhagen there is an area of exposed Cretaceous/Tertiary chalky cliffs that over look the Baltic sea.  The cliffs are white like the famous cliffs on the coast of southern England but closer examination reveals a strange looking grey band of clay about 8 cm wide running across them.  The locals call this fisk ler, translated this means fish-clay, due to the large number of fish bones found within it.  This clay band has been dated to 65 million years and is one of the few sites around the world where the K-T boundary layer is exposed.

Analysis of this clay layer has revealed evidence that supports the impact theory as the cause of the mass extinction.  Firstly the clay layer contains soot.  An asteroid impact would have thrown molten rocks up into the air and these would have caused forest fires when they landed.  An impact of the magnitude  of the Chicxulub event, would have thrown red-hot rocks all over the planet.  Any material ejected into the upper atmosphere would have become hot due to friction as it plunged back down to Earth, adding to the rain of incendiaries.  Some scientists claim that the soot layer is so dense in the deposits studied on the Baltic that if they had been laid down in just 1 or 2 years they could have produced by half the world’s vegetation burning.

Whatever the reason for the event, life on Earth was devastated, not only did the Dinosaurs, marine reptiles and Pterosaurs perish but also about 90% of all protozoan genera and algae went extinct too.  Marine plankton disappears from the micro-fossil record so abruptly that it forms a distinct boundary.   Deposits which show this distinct phase have been nicknamed the plankton line by geologists.

However, it is the humble fern that provides the strongest evidence of a sudden and dramatic single event devastating life on Earth. Studies of fossil spores and pollen (important elements making up micro-fossil sites), show that prior to the end of the Cretaceous fern spores make up about 25% of the percentage of total spore and pollen micro-fossils.  Flowering plants were dominant by the end of the Cretaceous period and it is the angiosperms that make the major part of fossil plant elements at micro-fossil level.  At the K-T boundary few spores and pollen fossils are found.   In the first part of the Palaeocene epoch (lower Danian faunal stage deposits), there is a sudden and dramatic rise in the fern spore component of the micro-fossil fauna and flora.  Indeed, in some sediments, fern spores make up 99% of micro-fossils recorded immediately post the end of the Cretaceous.

As the Palaeocene progressed the percentage of fern spores in the fossil record falls, eventually reaching levels seen prior to the mass extinction event.  This surge in fern spores is called the Fern Spike.

A Diagram showing Dramatic Fern Spike after the Cretaceous

Chart source: Everything Dinosaur (ref: R. C. Moran)

Many Palynologists (scientists who study pollen and spores), claim that the fern spike indicates a sudden and dramatic climatic catastrophe such as an impact event and not the thousands of years of volcanic eruptions as indicated by supporters of the Deccan Traps hypothesis.  Ferns are often the first plants to recover after forest fires and other natural disasters.  They are often at the vanguard of re-populating areas that have been severely polluted.  Could they provide evidence to support a collision with a body from outer space?

The fern spike seems to be a phenomenon that passes quite quickly in geological time.  It is certainly true that ferns are some of the first plant species to re-colonise ground that has suffered from a forest fire, but equally ferns are some of the first plant species to establish themselves on volcanic slopes and lava flows.  So perhaps the fern spike was caused by the dramatic and immense volcanic eruption phase 65 million years ago in India that led to the deposition of the thickest layers of basalt that now make up the Deccan Traps?