Australia: Ancient Life

Amidst the abundance of Western Australia's wildflowers are living things far older. Near the coast of the Indian Ocean, not far from the well-known Pinnacles of Nambung National Park, is a much less-visited site, Lake Thetis. The attractions at Lake Thetis are far from obvious, and our companions were no doubt a bit nonplussed at my insistence that we see them, on September 15, 2013, and my excitement when we did. They may not have looked like much, but they were testimony to the presence of some of the most ancient living things on earth.

Lake Thetis is one of the few places on the planet where you can see living stromatolites. If that statement doesn't set your heart racing, perhaps I may need to explain what stromatolites are. First, though, let's walk out to the lake.

On the way, we can check out the nearshore vegetation. It includes shrubs like Thick-leaved Fanflower (Scaevola crassifolia).  This is a coastal plant (as are many in its genus), found on dunes and limestone cliffs around much of Western Australia.  Its thickened leaves protect it against salt spray and windblown sand.

Clambering over much of the shrubbery are the stringy yellow stems of Dodder Laurel (Cassytha racemosa).  Like the unrelated "true" dodders (Cuscuta) Dodder Laurel is a parasite, drawing its nourishment from the stems of the plants that support its clambering vines.

There are, as always, plants I can't identify.  This one is awfully pretty, though.

 

This spray of flowers (some sort of myrtle, I presume) is being visited by a Common Grass-blue (Zizina labradus).

The closer we get to the salty waters of the lake, the more the vegetation becomes dominated by the salt-tolerant Beaded Samphire (Sarcocornia quinqueflora), a member of the goosefoot family (Chenopodiaceae).

The reddish stalks are probably last year's stems.  Fresh green shoots of samphire are edible (though I have never tried them), and apparently very good.  The odd name "samphire", first used for the British species, is apparently a corruption of "St. Pierre" or Saint Peter, presumably reflecting his supposed occupation as a fisherman.

Finally, as we reach the shore of the lake, we pass clumps of rushes (presumably members of the Southern Hemisphere family Restionaceae).

A wood-and-metal walkway takes us out onto the lake bed to see the stromatolites themselves.

Now that we are here, it is time to explain what stromatolites are.  They are not so much living creatures themselves as accidental constructions assembled around mats of cyanobacteria, the simple organisms once known as blue-green algae.  Cyanobacteria are not really algae, though.  True algae are, like ourselves, eukaryotes, with cells containing nuclei, mitochondria and other internal structures.  Cyanobacteria, like other bacteria, are prokaryotes, lacking such things.  They are actually more distantly related to true algae than we are.  Like algae, they photosynthesize.  In fact they were probably the first organisms on Earth to do so, and the photosynthetic structures in plant cells, the chloroplasts, are probably cyanobacteria that took up life within other cells over 500 million years ago.

Anyway, mats of cyanobacteria trap bits of sediment (a purely passive process; this isn't reef-building, though chemical activity by the bacteria can precipitate out compounds like calcium carbonate).  More bacteria grow over the silt-laden mat, and the result is a slow buildup, taking centuries or even millennia, into a layered mound with a shape like a giant head of broccoli.

The result, admittedly, doesn't look like much, but to see a living stromatolite is to gaze into deep time.  The fascinating thing about stromatolites is that cyanobacteria (and possibly other microorganisms) have been building these things for the last 3.5 billion years.  Fossil stromatolites are not only the earliest large-scale evidence of life on this planet; for most of the history of that life they are the only macroscopic record that life existed at all.  The fossils of the 500-million-year-old Cambrian Explosion are newcomers by comparison.

Today, stromatolites survive only in waters so hypersaline, or alkaline, that other, Johhny-Come-Lately organisms cannot survive there to disturb their slow, placid growth. Late Thetis (and more famously, Shark Bay well to the north) is one of a handful of places where they survive.  Here, we could imagine days, so very long ago, when (as far as life was concerned) unprepossessing mounds like this were, pretty much, it.  So there they are: living stromatolites - dull to look at, perhaps, but amazing to contemplate.