If the Earth has gradually grown in size over time, and enormous ocean beds built
between some continental land masses - it is quite understandable that the attitude
of the planet in relation to the Sun has also changed.
At the moment there is much confusion regarding palaeo-climates and hypotheses relating
to ‘Snow-ball’ and ‘green-house’ Earth conditions. The geological evidence is perplexing
- but all this can be resolved by the following study.
From the modelling of the Earth’s size and continental positioning through time,
it is possible to assess where the equatorial line, or more precisely speaking, the
magnetic equatorial line was situated at a given time. There are three main indicators
which betray areas of maximum insolation. These are:-
1) Fossil distribution (particularly land animals)
2) Coal Measures
3 The presence of evaporites in areas which were once desert.
Also there are signatures from glaciation which can indicate the boundaries of these
And, as explained in the chapter on A Mechanism for Planetary Growth, the equatorial
line is the area where bulging of the planet mostly takes place and this is accompanied
by volcanism and intrusion. This bulging phenomenon is likely a result of compound
formation within the mantle below the crust as ions come together. As a consequence
- traps, batholiths, volcanoes and igneous provinces should have their beginnings
during different palaeo-equatorial positionings. The thinning out of the Earth’s
crust at particular areas should also relate to those areas being within the palaeo-equator
at a certain point in geological time. For example, much of Australia, will have
‘thinned out’ during the Permian and Triassic Period when it was on the equator.
Today areas such as the islands of the Indonesian Archipelago, on the Sunda Shelf,
are on the equator and crustal thinning will be taking place and causing the islands
to separate further from each other.
Volcanism can enhance local temperatures and affect micro-climates - and so we have
to allow for this too, especially when considering the most primitive forms of life
and the earlier geological times.
If we consider Pangaean Earth to have had a maximum equatorial temperature of 25
degrees C, (like Mars has now) 328 million years ago, and this has increased to a
present maximum equatorial temperature of 50 degrees C; this is equivalent to 0.07
degree C increase every million years. This gives a preliminary setting for the palaeo-climate
We must also understand that this band of insolation widens as the planet gets larger
in diameter. Hence, the distribution of animal and plant fossils should widen with
the width of this band. It can be understood that the equatorial region is the least
seasonally variable part of the planet and the early terrestrial life forms will
have required an environment which stays the same throughout the year.
But as time passed, certain plants and animals were able to adapt to the seasonal
changes experienced in areas further away from the equator. Some insects, for instance,
were later able to adjust their life-cycles, so that stages of their metamorphosis
were better suited to the seasonal climatic changes. In the plant world, trees like
conifers would become adapted to survive colder wintry seasons at the edges of the
With regards to evaporites, only since Jurassic times will these have formed - when
the Earth was half the distance between Mars and its present position. This is because
a planet in Mars’ position receives only half the amount of sunlight of that of Earth.
Consequently hot evaporative conditions would not exist.
Concentrations of salts that predate Jurassic times, however, do exist. This may
suggest that another process of salt concentration can take place - such as the natural
freeze-drying of up-welling saline solutions and the later sublimation of its ice
component. This phenomenon is happening today in Antarctica at Lake Fryxell. Lawrence
and Hendy (1958) observed brine concentration forming in extreme cold/dry conditions
and remarked that evaporites are usually considered to be manifestations of hot,
dry climates. This could be the process by which the evaporite domes on Ellef Ringnes
Island (Baffin- near Greenland) could have developed in the Devonian Period.
The Fossils of the first four-legged land animals
Fossil evidence tells us of the distribution of the earliest land animals and plants.
If the dating of these fossils has been correct, their distribution should indicate
paleo-climates through the ages and these should conform to the modelling parameters.