Readings: Erectus SE Asia, Devonian Fossil Forest, Archean Iron Formations

Some selected readings:

1) New dates of Homo erectus from Ngandong Java shows late surviving populations until 117,000 to 108,000 years ago. A short clean summary by Razib Khan on SE Asian hominin diversity.

Southeast Asia during the Eemian was a hominin paradise.

Paper: Last appearance of Homo erectus at Ngandong, Java, 117,000–108,000 years ago.

2) Exquisite preservation of one of the earliest forests from the Mid Devonian ( ~385 million years ago) of New York containing a modern looking root system.

Paper - Mid-Devonian Archaeopteris Roots Signal Revolutionary Change in Earliest Fossil Forests.

Write up : The World’s Oldest Forest Has 385-Million-Year-Old Tree Roots.

3) Before around 2.3 billion years ago there was very little oxygen in the atmosphere. This was a time before the evolutionary invention of oxygenic photosynthesis wherein bacteria harvest electrons from H2O and release oxygen as a byproduct. Instead, during this time another photosynthesis pathway known as photoferrotrophy was prevalent. Here, bacteria use light and ferrous iron (Fe+2) to fix CO2 as biomass, releasing ferric iron (Fe+3) as byproduct. This ferric iron then accumulated to form large iron deposits. But these deposits lack organic matter. How to explain this if the iron was being produced from a biomass? Scientists point to a role of silica. At that time the oceans were saturated in free silica. Experimental work shows that in the presence of free silica cell surfaces repel iron hydroxides, thus creating a source of organic matter free iron deposits. This organic matter then was acted upon by methane producing microbes. The methane released kept the temperature of the earth warmer than it would have been under a dim early sun.

Fascinating story of the feedback between geology and evolution.

Photoferrotrophy, deposition of banded iron formations, and methane production in Archean oceans.

Rhizome Structures Of Early Plants And Their Impact On Paleosols And Landscapes

From time to time it is instructive to move away from the subject of animal evolution that does tend to dominate media reports. From a sedimentology perspective, plant evolution too has played an extremely important role in shaping sediment composition and fabric, fluvial architecture and the structure of our landscape:

Belowground rhizomes in paleosols: The hidden half of an Early Devonian vascular plant- Jinzhuang Xue et.al. 2016

The colonization of terrestrial environments by rooted vascular plants had far-reaching impacts on the Earth system. However, the belowground structures of early vascular plants are rarely documented, and thus the plant−soil interactions in early terrestrial ecosystems are poorly understood. Here we report the earliest rooted paleosols (fossil soils) in Asia from Early Devonian deposits of Yunnan, China. Plant traces are extensive within the soil and occur as complex network-like structures, which are interpreted as representing long-lived, belowground rhizomes of the basal lycopsid Drepanophycus. The rhizomes produced large clones and helped the plant survive frequent sediment burial in well-drained soils within a seasonal wet−dry climate zone. Rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants. Predating the appearance of trees with deep roots in the Middle Devonian, plant rhizomes have long functioned in the belowground soil ecosystem. This study presents strong, direct evidence for plant−soil interactions at an early stage of vascular plant radiation. Soil stabilization by complex rhizome systems was apparently widespread, and contributed to landscape modification at an earlier time than had been appreciated.

My interest in this subject is a little tangential. It deals with how to recognize unconformities and disconformities in the field in carbonate sequences. During episodes of sea level falls, marine basins covered by layers of calcium carbonates shells and skeletons get exposed to atmospheric elements. Plants colonize this exposed surface and their root systems physically disrupt the layers of sediment. Rain water and organic acids released by plants dissolve sediments creating pore spaces. The disruption may be clearly visible as solution pits and collapse structures... a karst topography...

I have written a detailed post about this topic and so I won't repeat the lecture over here except to put up this image of a karst developing on Pleistocene limestones from South Florida. Notice how chemical dissolution and the action of roots have caused collapse pits on the limestone surface - 

Land Plants And Expression Of Disconformities in Limestone Sequences

Do read..