47 Tuc and a Fossil Riverbed

7 Oct 2016

Astronomy is colossal – the size of stars, their ages, the distances between them, the power of supernovae, the nature of black holes, the size of galaxies, superclusters, and the universe itself. But to me, most colossal of all is time. The enormities of time, the complexities of time past, present and future boggle my brain. At one end of the scale, I look at my dear little dog, Waldo, and think of the handful of time that measures his life. At another end of the scale, I look at 47 Tuc, whose stars are almost as old as the universe itself – and I think of the unimaginable time that measures its life and the vast void of space and time that 16,700 light-years away denotes.

Along with a love of astronomy, I love rocks and fossils, and am a keen rockhound – and it is probably the time factor that I find so fascinating with them. Now and then I go fossil-hunting in the Karoo with a paleontologist friend on mine. When it comes to fossils, it’s normally the big animals that get the most attention… I like plant fossils and I have a magnificent hunk of a 260 million year-old petrified glossopteris tree. I get the most extraordinary sense of intermingled geological and astronomical time when I look at that great hunk of petrified tree and consider that in the time since that tree fell down and underwent its process of permineralization, the solar system has done a full trip around the Milky Way Galaxy.

Going back even further in time, I have a rock from the Barberton Greenstone belt in Mpumalanga which, at almost 3.5 billion years old, is one of the oldest and best exposed Archaean greenstone belts on Earth. It is extraordinary to hold this rock in your hand and consider that single-celled life on Earth had begun roughly 300 million years before this little hunk of rock formed. And the rock had roughly another 700 million years of life-time before multi-cellular life evolved. And it was almost 3 billion years old before the kind of life forms we are more familiar with began to evolve.

Time. Rocks. Fossils.

Who’d ever have thought that all three come together less than 30 kilometres away from van Zylsrus here in the Kalahari?

The Kalahari landscape is an arid savannah foreverness of rolling red sand dunes, salt pans, and undulating grasslands that stretch to every horizon. With no warning beyond a few scattered boulders lying here and there in the veld, you come across this formidable canyon. It’s part of a fossil riverbed – the relic of the mighty Molopo River that stopped flowing perennially right around the time 47 Tuc’s light left on its journey to Earth.

The evolution of the Molopo River was influenced by tectonics, climatic change, and of course, time: the progressively more arid conditions resulting in this vast dry 960 kilometre riverbed (rising in Mafeking, and originally emptying into the Orange River down near the Augrabies Falls). For the most part it is a wide, shallow sand riverbed, but with a few impressive rock-cut gorges like this one. (The Molopo Riverbed forms a significant length of the border between South Africa and Botswana. The fence in the photo is the border; Botswana to the right.)

The rock formations in this canyon are spectacular, and I am dumbfounded at the thought of the might of this river that carved these rocks into these beautiful forms. And the eons of time involved.

During above-average rainfall years, floods may occur in response to short-term high intensity rainfalls in the upper reaches of the Molopo River. It has been known to have flooded in 1891-92,1896, 1915, 1917-18, 1933-34 and 1988, but the various records indicate it only flowed as far as Bray (about 360 kilometres from Mafeking and a rough 300 kilometres upstream from this canyon). There are no records of the Molopo flowing beyond there.

More rock formations. This is rockhound heaven!

Our post-walk picnic waiting under a Camelthorn tree at the entrance to the canyon. Sitting there munching on my sandwich it wasn’t hard to wonder how many people ever come to this remote and extraordinary place. I suspect not many.

Needless to say, the evening’s observing was all about 47 Tuc.

Sitting at my telescope, looking at that gorgeous globular cluster, the universe has never felt so grandiose. I’ve looked at this beauty uncounted times, the scale of it is staggering… hundreds of thousands of 13 billion year-old stars stuffed into a ball about 120 light-years across, roaming the halo of our galaxy, its light taking around 16,700 years to reach us.

But last night I ‘saw’ something different: the scale of a mighty river measured in the astronomical.