Geological Time Scale
and
Namibia
The beginnings of our planet formed some 4.5 billion years ago and the
Geological Time Scale lower down represents
the ongoing development of the earth, its seas and land masses.
Early life began in the seas
about 3,500 million years ago in the Archean Era, but it was not
until the Paleozoic Era, about 570 million years ago that a
profusion of marine invertebrates developed such as cephalopods,
corals, gastropods, trilobites and worms. The early fish were
invertebrates having their bodies within 'armour casings'. The
first vertebrates appeared about 500 million years ago and fish
evolved into creatures having a bone skeletal frame and became the
dominant vertebrate. About 410 million years ago certain species of
fish developed into amphibians and began to colonize the land. It
was about 360 million years ago that the early reptiles evolved and
they in turn began to displace the amphibians as the dominant land
species.
Geological Time Scale
used is as determined by
the International Committee on Stratigraphy (ICS)
1. Eons are the greatest chronological divisions of which
there are four. The Hadian and Archean being the earliest 2.5 billion years
of the Earth's development, followed by the Proterozoic, 1.5 billion
years, and the Phanerozoic which began 542 million years ago until today.
2. Eons are subdivided into Eras.
(a) The Proterozoic is subdivided into the Palaeoproterozoic,
Mesoproterozoic and Neoproterozoic Eras.
(b) The Phanerozoicis subdivided into the Palaeozoic,
Mesozoic and Cenozoic Eras.
3. Eras are subdivided into Periods.
(a) The Paleoproterozoic into the Siderian. Rhyacian,
Ososirian, Stratherian and Calymmian.
(b) The Mesoproterozoic into the Calymmian, Ectasian and
Stenian.
(c) The Neoproterozoic into the
Tonian, Cryogenian and Ediacaran.
(d) The Paleozoic into the Cambrian, Ordovician, Silurian, Devonian and Carboniferous.
(e) The Mesozoic into the Permian, Triassic, Jurassic
and Cretaceous.
(f) The Cenozoic into the Palaeogene and Neogene.
4. Periods are subdivided into Epochs.
Plate Tectonics
It was as
early as 1620 that the English philosopher Francis Bacon commented
on the apparent similarity of the shape of the West coastline of
Africa and the Eastern coastline of South America. However, Bacon
made no reference
that the two continents could have once been joined. In 1858, an
American called Antonio Schneider made the suggestion that the
continents had somehow moved in respect to each other. But, it
was not until 1915 that German meteorologist Alfred Lothar Wegener
(1880-1930) published in his book, 'THE ORIGIN OF CONTINENTS AND
OCEANS' the theory of
Continental Drift
. Wegener proposed that the
earth had once consisted of a single land mass surrounded by a vast
ocean. He named this super continent
Pangaea and explained that it
had long ago divided forming two great continents -
Laurasia in the
North and
Gondwana in the South and that, in time, these two
continents had further divided.
Wegener's theory was viewed
with scepticism by the Geological fraternity until the 1960s by
which time advanced scientific measuring equipment had been
developed and the phenomenon of Paleomagnetism was accepted.
Go to Tectonic Plate Palaeo Maps
Earth 'entering new age of
geological time'
The Earth has entered a new age of geological time – the epoch of new man,
scientists claim.
“The Anthropocene represents a new phase in the history of
both humankind and of the Earth, when natural forces and human forces became
intertwined, so that the fate of one determines the fate of the other.
Geologically, this is a remarkable episode in the history of this planet.”
more► Report 24 April
2010
