Readers’ wildlife photos

February 22, 2023 • 8:15 am

Today we have some lovely geology photos, relating to the early Earth, from reader Rodney Graetz. Rodney’s narration is indented, and you can enlarge his photos by clicking on them:

Pages from the history of planet Earth

The history of planet Earth is recorded by its rocks in the language of their composition and age, and we have only recently been able to read it.  The history is a significant component of human understanding.  It informs us about Early Earth events, such as the origin of Life, and exposes the absurdity of our creation myths.

Here are eleven Australian pages from Earth’s History.

The most interesting pages in Earth’s history are the oldest, for Deep Time is a synonym for Early Earth.  Some Australian landscapes contain old rocks, and one area, The Pilbara, has become an international focus for Early Earth research.

This is a typical Pilbara landscape looking hot and subdued by age.

At my feet was this layer-patterned rock, a fossilised stromatolite – a structure that is recognisable because living stromatolites still exist.  They are the result of a repeated sequence of sticky film-living, bacteria-like life forms being covered by fine sediment, then a new living film is generated and covered, and so on.  The age of this fossilised life is 3400 million years (My),one of the oldest, globally.  The Earth formed at 4543 (My) ago so, the Earth’s age when this stromatolite formed was (4543-3400), or1143 (My).  It took more than a billion years for Life to appear in Earth’s history.

A low conical hill at dawn, topped with an incongruous cap.  It also has that old, subdued look, and rightly so for measurements revealed the cone to be deeply weathered granite aged at 2950 (My), or Earth Age 1600 (My).  The cap rock is of a ‘young’ sandstone of ‘dinosaur’ time, 146-66 (My).

A broken block from a layer of fossilised stromatolites strikingly illustrates its structure, the repetitive layering of life activity and its burial.  Aged as 2740 (My).  Earth Age 1803 (My).

During the period 2470 – 2450 (My), the oceans ‘rusted’.  The soluble (Ferrous, green) Iron compounds were oxidized to insoluble (Ferric, red) form and precipitated out.  The proposed cause was increasing and fluctuating atmospheric oxygen known as The Great Oxidation Event.  The result was this example of Banded Iron Formation (BIF), known globally from many areas of ancient rocks, and the primary source for contemporary iron mining.  Earth’s landscapes, rocks, and soils have been ferric red ever since.  Earth Age 2073 (My).

Leaving the Pilbara, and moving to Northern Australia, this rock is uninteresting in appearance but puzzlingly isolated on a floodplain.  Its measured age is 1800 (My), Earth Age 2743 (My).  Much more interesting is that this outcrop, and the crust it is part of, was once a component of a now-dispersed supercontinent, Nuna/Columbia, located at 30° N, or approximately 5000 km (3000 mi) from where it is today.  The Earth’s crust, in action.

Now to Southern Australia, the Flinders Ranges.  A vertical-up photograph of a rubble-like rock layer overlying a totally different rock type.  The top layer of various sized boulders, gravel and sand is the unmistakable signature of glacial action, that was progressively discovered to be both massive and extensive.  Mapped globally, it was named the Cryogenian Period, 720 – 660 (My), but because it was found to be so widespread over 60 (My), it is thought the entire planet was frozen, the so-called Snowball Earth, or more correctly, Icehouse Earth.  Earth Age 3826 (My).

A ‘golden’ spike that Internationally defines the lower boundary on the geologic time scale.  In 2004, it marked the recognition of a new chapter in Earth’s history.  The beginning (rocks above the marker) of the newly-recognised Ediacaran Period, 660 – 540 (My), containing fossils never before seen.  The rocks below the marker are from the Cryogenian Period.  Earth Age 3883 (My).

The finger points to an unusual rock layer: unusual in that the particles within it are all angular and varied in size.  Interpreted only in 1986, this layer is an ejecta layer from a bolide (meteorite) impact at 590 (My), that created a 50+ kilometre wide crater (20-30 mi) now eroded to a salt lake, Lake Acraman.  This sample of the ejecta layer is about 300 kilometres (190 mi) distant from the crater.  Earth Age 3953 (My).

This fossil-filled rock was formed at 525 (My), Earth Age 4018 (My).  The fossil is an Archaeocyath, meaning ‘ancient cup’.  The circular sections are of a barrel shaped body.  The Archaeocyath are a now-extinct group of marine sponges that were important in forming the first reefs on Earth.  The location of these fossils has been recommended as a World Heritage site.

Back in Northern Australia.  This cliff bordering the Fitzroy River appears unusual in shape, colour, and layering.  Dated at 350 (My), Earth Age 4193 (My), the cliff was once part of a large, fossil-rich, reef.  Known as the Kimberley Fossil Reef, it is horseshoe-shaped and hundreds of kilometres in extent.  Nearby, there are numerous areas of high-quality, fish fossils, the first back-boned animal.  Until then, all land surfaces were lifeless, but from this time on, green (photosynthesizing) plants began invading the land and changing the colour of planet Earth.

Shark Bay, Western Australia, declared a World Heritage site to preserve a large populations of living stromatolites.  This very small sample captures their variation in area and shape, but notice the uniform height determined by tidal variation.  It is a way of living – a signature of Life – that has persisted for at least 3400 (My).  Earth age 4543 (My).

21 thoughts on “Readers’ wildlife photos

  1. The Earth formed at 4543 (My) ago so,

    The precision of dating methods has reached the point these days that the period of time it took for the Earth to form starts to become significant. While it’s hard to know for sure, modelling suggests it took between 5 and 30 million years to assemble the Earth (and the other “rocky planets”) from planetesimals orbiting the Sun. (Improving astronomical data could narrow down the variations in the plausible modelling over the next few years.)
    A useful date to remember is that components of meteorites (and thence, asteroids) which were melted in the initial “turning on” of the Sun (“CAIs” – Calcium-Aluminium rich Inclusions) give an age of 4567 Myr, These CAIs are thought to predate (slightly) the assembly of planetesimals into the rocky planets. Whether or not Jupiter had formed, or was forming, at that time is uncertain.
    Then of course, there is also the “Moon forming” impact. Which may have been as much as 100 Myr after the construction of the planets started. That’s starting to get awkwardly close to the date of the Jack Hills zircons (4404 Myr BP [Before Present] ; 139 Myr “Earth Age” in Rodney’s terminology) ; the awkwardness being that the oxygen isotopes in those zircons suggest that they formed with the involvement of water that had been through multiple rainfall-evaporation cycles (“meteoric” versus “primordial” water). Could the Jack Hill zircons actually date to a period before the “Moon forming” impact?

    the Earth’s age when this stromatolite formed was (4543-3400), or1143 (My). It took more than a billion years for Life to appear in Earth’s history.

    Alternatively, it took not much more than a billion years for life to evolve on Earth. That’s still slightly surprising, to me. So rapidly?! The Earth then was still a very dynamic place – the heat flow from radioactive decay would have been around 3 times higher than today, and with a somewhat higher contribution from the impact heating during assembly. There would have been a lot more volcanic activity than today. Now if Rodney’s photography had included some “spinifex” brush, we’d have an opening to discuss komatiite lavas, between 300 and 500 K hotter than the hottest lavas today. But without that we’ll just have to muse on meteorite impacts tens of times more energetic than the Chixulub “dinosaur killer” impact at the Cretaceous – Palaeocene boundary, happening every few million years. And early life survived this!

  2. Awesome walk through a huge expanse of time. Thank you! I’m always amazed at how Australia is home to both super-ancient fossil stromatolites and to the modern ones in Shark Bay. Modern stromatolites are rare in today’s intertidal because snails and other creatures eat the organisms that form the algal and bacterial mat. If I’m not mistaken, Shark Bay is hypersaline, which keeps snails at bay and allows the stromatolites to form unmolested.

  3. I add my thanks for those wonderful photos and your equally wonderful commentary. I found myself curiously moved by the whole thing. I look forward to much more information about the earliest life on earth. Thank you again.

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