Before 380 million years (Ma) ago, the continents had only patches of mosses and algae with no tree cover. The effect of the evolution of trees (large vascular plants with deep, extensive roots) changed the world for ever, according to Dr Robert Berner (Yale University). He presents his findings at Earth Systems Processes, a multidisciplinary meeting in Edinburgh, UK, hosted jointly by the Geological Society of London (GSL) and the Geological Society of America (GSA).

The first trees soaked up nutrients from rocks at a rate never before seen. This enhanced the weathering of calcium (Ca) and magnesium (Mg) silicate minerals, which in turn removed carbon dioxide from the atmosphere as Ca and Mg became locked together with carbonate ions in lime-rich sediments in the worldís oceans. The removal of CO2 from the atmosphere by this method and by increased photosynthesis (fixation) led to atmospheric CO2 stabilising at lower levels than the world had known for most of its previous 4200Ma history.

Trees also produced, for the first time, large amounts of lignin – the major constituent of wood. Resistant to decay, this substance led to increased amounts of organic carbon being buried with sediments, representing a large excess of global photosynthesis (carbon fixation) over global respiration (carbon oxidation). As atmospheric carbon dioxide was progressively reduced and photosynthesis reached unprecedented levels, the atmosphere became extremely rich in oxygen ñ much richer than the air we know today.

Oxygen-enriched air was directly responsible for the evolution of very large insects – much larger than could live in todayís relatively oxygen-poor air (insects rely upon more or less passive diffusion of O2 into their tissues, so large bodies become impossible at lower concentrations).

As well as the formation of huge coal deposits well known from Upper Carboniferous (Pennsylvanian) rocks worldwide, this radical shift in the Carbon Cycle also lowered the global greenhouse effect and led to global cooling, giving rise to long-term glaciations. The effect of deforestation on the modern world climate cannot therefore be underestimated at a time when global liberation of gaseous CO2 (through the burning of carbon fixed and buried in the Earthís distant past) is at an all-time high.



Contact: Ann Cairns
303-447-2020 x1156
Geological Society of America

During the Earth System Processes meeting, June 25-28, contact the GSA/GSL Newsroom at the Edinburgh International Conference Centre for assistance and to arrange for interviews: 44-131-519-4134

Ted Nield, GSL Science and Communications Officer
Ann Cairns, GSA Director of Communications

The abstract for this presentation is available at:

Post-meeting contact information:

Robert Berner
Dept. Geology & Geophysics
Yale University
210 Whitney Avenue
New Haven CT06520-8109, USA
TEL: 01-203-432-3183
FAX 01-203-432-3134

Ted Nield
Geological Society of London

Ann Cairns
Geological Society of America
01-303-447-2020 ext. 1156

To view other Earth System Processes press releases, see