The Structure of the Earth

  In order to appreciate the flora and Fauna of the Valleys of the Blue Mountains, it is  a prerequisite to quickly see how they came about. 

The timeline of the structure of the earth is an intimidating collection of data spanning  billions of years.

The Earth is about 4.54 billion years old.

The geological clock: a projection of Earth's 4,5 Ga history on a clock ("MA" = a million years (Megayear) ago; "GA" = a billion years (Gigayear) ago)  File:Geologic_clock.jpg

This clock representation shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga.[1] Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.

Lithified stromatolites on the shores of Lake Thetis, Western Australia. Archean stromatolites are the first direct fossil traces of life on Earth.   Stromatolites at Lake Thetis, Western Australia. Date 30 March 2006 Source Author Ruth Ellison

The Earth’s crust is very thin, extending to depths of 30 to 65 km under the continents, and only 5 to 15 km under the oceans

hidden deep beneath the mantle at a depth of 2,885 km is the outer edge of the Earth’s iron-nickel core – the peach pit if you will! But the similarities end there. The inner core may be solid, but the outer part is hot metallic liquid – the only liquid layer in the planet.

The uppermost mantle, along with the thin crust, defines a fairly rigid layer known as the lithosphere. The lithosphere ranges from 10 to 250 km thick and is broken into fragments, called plates, which move around the Earth like pieces of a giant jigsaw puzzle.

Below the lithosphere, enormous heat creates convection cells in the deeper mantle. The stiff lithospheric plates are carried along by these currents of hot flowing rock, much like a conveyor belt. The movement is slow – not much faster than your fingernails grow – but over geologic time, the effect is very dramatic. As the plates move, they carry with them the parts that poke above the water – the continents and islands – and in so doing, constantly reshape the geography of our planet!

This activity, known as plate tectonics, has not been steady over time. Some periods were calmer; others, like the Devonian, much more intense. Where plates moved apart, oceans formed, and where they pushed against each other, continents collided and the towering majestic peaks of new mountain chains emerged from the disappearing Devonian seas...

Over the past centuries the names of famous divisions in the geologic timescale began to emerge – l the Cambrian, Silurian, Carboniferous, Jurassic and Cretaceous periods – and these were named after historical or contemporary regions where the rocks of that period are plentiful (Cambria and Jura, for example), or where the rocks reflect the dominant characteristics of the time (“Age of Coal”, “Age of Chalk”, etc.). The geological timescale was finally, albeit slowly, taking shape.