Sudwala rocks of life EarthCache

More than just interesting for the evidence they present of early Precambrian life, these stromatolitic dolomites represent a mile stone in earth’s history that is as easily overlooked as it is fundamentally important. The early life forms that helped build these very dolomites also provided the earth’s first oxygen, without which the higher forms of life would not have evolved.

From the co-ordinates of the EarthCache GC1TR1M, you can see on top of the hill very good examples of stromatolitic dolomites that stand out with the surrounding soil being weathered away.

Malmami Dolomite; Earth’s first oxygen generator
The Malmami dolomite (and its equivalent Campbell Rand |Dolomite in the Northern Cape) is part of the Transvaal Super group that was deposited in a vast inland sea on the Kaapvaal Craton. It makes up a two thousand meter thick carbonate sequence over large parts of central South Africa. Now occurring in two well defined structural basins, these were connecting during the time of there formation 2600 to 2400 million years ago.

Dolomite is a fine grained, calcium-magnesium carbonate rock, originally formed by the slow accumulation of microscopic grains of calcium carbonate in a warm tropical sea. This process was intimately involved with the production of layers of sticky algal growth, called algal mats, in the very shallow intertidal to sub tidal zone. If you look closely at the well edged, weathered outcrops, you will see several diagnostic clues to the organic origin of the dolomite. Notice a fine crinkly lamination that reflects the original sticky algal mats or layers that formed on the sea floor and trapped or precipitated fine carbonate material. Look, on a larger scale, for small to large rounded or elongated dome like structures, called stromatolites, which clustered in coral like reefs in the shallow sea, and were earth’s prolific life form at the time. These mound-like features are the fossilized remains of large masses of algal mat build up that were shaped by tidal currents. And if you could look through a high powered microscope, you might also see traces of minute, single cell micro organisms preserved in the rock. These are the remains of the 2.5 billion year old blue-green algae, not very different from those existing today. Modern day algal mats are rare, but are known from Shark Bay in Australia, where living stromatolites can still be found in a strongly saline, shallow sea.

Photosynthesis process:
The rock was not the only thing that the blue-green algae, or cyanobacteria, gave rise to. By the process of photosynthesis – active even in matter as primitive as algae – the cyanobactria where busy converting primeval carbon dioxide into oxygen on a vast scale, and slowly releasing it into the sea. There the oxygen first combines with iron to form vast sedimentary, layer formations rich in iron; later, it was released into the atmosphere, hitherto dominated by carbon dioxide and nitrogen. Photosynthesis continued over a very long time, and oxygen to be “pumped” into the atmosphere. Slowly, the protective ozone layer build up, increasingly shielding the earth from deadly ultraviolet radiation. This paves the way for the evolution of the multi cellular organisms, and then the emergence of life from primeval oceans onto the land.

(Acknowledgments: Geological Journeys by Nick Norman and Gavin Whitfield).

To get credit for a find on this EarthCache you need to answer the following questions in a mail to the cache owner.

1. Take a picture at the listed waypoint with the stromatolitic dolomites clearly visable and attach the photos in your log.
2. Please indicate in the mail to the cache owner; how many stromatolitic dolomites are next to each other over a distance of 20m?
3. Estimate the overall width of a single stromatolitic dolomite?
4. Estimate the height of the stromatolitic dolomites from the road surface?
5. Explain the dolomite structure at the listed waypoint? (ie colour, grain size)