Melvyn Bragg and his guests discussed ice ages, periods when a reduction in the surface temperature of the Earth has resulted in ice sheets at the Poles.
The 6,000 km plus journey of the India landmass (Indian Plate) before its collision with Asia (Eurasian Plate) about 40 – 50 million years ago.
Although the term 'ice age' is commonly associated with prehistoric eras when much of northern Europe was covered in ice, we are in fact currently in an ice age which began up to 40 million years ago.
Fossil patterns across
Geological evidence indicates that there have been several in the Earth's history, although their precise cause is not known. Ice epochs have had profound effects on the geography and biology of our planet.
From this BBC radio programme “In our Time” I learnt some things I hadn’t realised and with the interest we have in the earth today, the technologies that are allowing us to explore and find out more ... I thought I’d highlight a few aspects I found fascinating ...
The earth is about 4.55 billion years old, during which there have been five major epochs conducive to the growth of ice at the poles.
In between - the ice comes and goes – sometimes for long periods of hundreds of thousands of years, at other times over a slightly shorter time frame of only tens of thousands of years.
The term ‘Ice House Earth’ is used when there is glaciation on one or both poles – it is estimated that this has occurred for about 15% of earth’s existence, and where we are now – a propitious time for the human being as we know him.
A geographical map of Africa,
showing the ecological break
that defines the Saharan
area. (Wikipedia: Sahara)
The other 85% of the time this earth planet has been in the Greenhouse inhospitable state ...
I had no idea that Gondwanaland (the huge landmass of five joined ‘southern’ continents) sat over the South Pole – glacial evidence is to be found in the Sahara...
... while the northern hemisphere landmasses, where the coal fields are now found, used to be in the tropical belt around the equator; from where the lush forests were able to grow in that warm tropical environment.
The shifting tectonic plates leave marks in the glacial moraines on the rock platforms giving geologists their evidence, while the seas and oceans back up and provide further developmental evidence of these changes to the earth.
Boundary for 20 degC isotherms.
Most corals live within this boundary.
(Wikipedia: Coral Reef for more info)
The sediments at the bottom of the ocean give us a valuable archive of past climatic activity – the records are continuous and can be dated – providing scientists with a ‘laboratory’ for the continuing collation of evidence.
Coral reefs provide recent evidence, but also those reefs preserved in the sedimentary layers hold historical evidence ... as corals only grow at temperate sea level they reflect these sea level changes ...
... giving us a ‘tidal mark’ in the passage of time, as the ocean levels rise and fall, and the fact that the continents had drifted away from the temperate regions.
North Sea: showing northern Europe and the British coastline – Dogger Bank in red is a large sandbank that probably was a moraine ... and formed one of the land links from Europe to Britain; the English Channel could also be walked across.
... the oceans and seas are a recorder as well as a connector between the rest of the earthly land masses ... the continents continued to move – and as they did the ice slowly melted ... or froze up again ... the earth is in a constant state of change ...
... as an ice sheet grows it locks up the water from the oceans, so the sea level will fall ...
... 20,000 years ago the sea was 100 metres lower than today (at the last glacial maximate), but 125,000 years ago the sea level was about 5 – 6 metres higher than it is today ....
|Getting set to go on April Fool's Day -
A - Z Challenge here we come!
20,000 years ago the United Kingdom was connected to the main land of Europe – when dinosaurs walked the earth ... and as man was starting to inhabit these northern environs ...
This will take us into my next few posts before the A – Z challenge ... man walked the earth – how and why did he get where he is today ...
Life is so interesting ... the coal forests of North America, the UK, northern Europe/Asia and China were formed in the tropics; while Antarctic explorers might have been ‘chasing’ deserts; then if those ice epochs had not occurred ... would we be here at all ...
The BBC's 'In Our Time' Radio 4 programme hosted by Melvyn Bragg
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