A Snowball Earth or......?

Barry and Helen Setterfield
May 16, 2003

 

Introduction

The Sturtian Sequence

The Marinoan Sequence

Interpretation of the Data

 

 

Introduction

Some creationists argue that the entire geological column is a construct which cannot be found on the real earth.  It needs to be stated clearly that there are four major divisions of geologic strata which are present everywhere around the earth, and in the same order.  The uppermost, or the one we live in and on is referred to as the Cenozoic.  There are three major divisions under it, in the same order all around the world.  The next division, or era down, is the Mesozoic.  The one below that is the Paleozoic.  The deepest era, or division we are aware of before we hit basement rock is referred to as the Archaeozoic ‘era’. 

 

Cenozoic era

Mammals, flowering plants dominant

Mesozoic era

 Large reptiles, birds, palms and pines dominant

Paleozoic

 

Insects, amphibians, algae, mosses, ferns dominant

Begins with Cambrian strata

Archaeozoic  (in more detail below)

Ediacara fossils present in some areas, below which are only bacteria and stromatolites

Marinoan

Sturtian

Torrensian

Willouran

 

Within each of these four general eras there are a number of subdivisions.  Not every place on earth has each of the subdivisions belonging to each of the major eras, but the major eras are always present.  Where a given subdivision is present, it has the same characteristic rock and fossil types worldwide, however.

Also world-wide is the evidence of three separate catastrophes of major proportions separating the four major divisions shown above.

Cenozoic
-- Cretaceous/Tertiary Extinction

Mesozoic
-- Permian Extinction

Paleozoic
-- “Snowball Earth” – or….?

Archaeozoic

Although there are many things which can be said about the different eras and their associated catastrophes, the one being dealt with here is the catastrophe which has been called by some the “Snowball Earth”.  This is a hypothesis attempting to explain some unusual characteristics found in the rock formations in the upper part of the Archaeozoic era strata around the world.  The material for this paper is being taken from the formations associated with these strata found in South Australia.

First of all, to help picture the material being referred to later, here is a slightly more detailed chart of the Archaeozoic strata.

 

Below the Cambrian Strata are the "Precambrian" or Proterazoic 'eras'.  The top two major divisions,  the Marinoan and the Sturtian are the areas which have given rise to the theory of an earlier "Snowball Earth".

  Cambrian "Cambrian explosion" of fossils, mainly limestones and sandstones
  Proterozoic/Cambrian boundary ---------------------------------------------
 
In a few places around the world there is an extra strata here containing the Ediacaran fossils
quartz sandstone

S

N

O

W

B

A

L

L

 

Marinoan

"upper glacial sequence"

Nucaleena Formation – dolomite (a kind of limestone)

Elatina Formation – includes Reynella siltstone (finely-layered, red-colored sediments with dropstones embedded) and Whyalla sandstone, as well as other slates and quartzites.

Purple, gray, and green slates and shales

Quartzites

Chocolate slates

E

A

R

T

H

Sturtian

"lower glacial sequence"

Brighton limestone – a carbonate capping  to the rest of the Sturtian sequence below.

Tapley Hill Formation – finely laminated siltstone

 Diamictites -- debris of various sorts and sizes of rock in a cement-like matrix

  Torrensian

Belair subgroup quartzites, slates, and shales

Dolomites – a sort of limestone

Stonyfell quartzite

Aldgate Sandstone

  Willouran

Mainly Quartzites

Basal conglomerate

Basement Rock

 

Geologists have become very aware of a suite of rocks that occurs almost worldwide near the Proterozoic/Cambrian boundary. The designation of this grouping of rocks is sometimes given as the Infra-Cambrian or, more often, as the Neo-Proterozoic. On the atomic or radiometric timescale used by geologists, these strata date from around 750 million atomic years down to something less than 600 million atomic years. The strata shown in this article all come from the southern suburbs of Adelaide, South Australia. This area is known as one of the type-sections showing the strata at this level, as evidenced by the fact that both the Sturtian and Marinoan sequences get their names from this part of Australia even though they are found around the world.  The photographs in Part 1 are of rocks that are all dated towards the higher end of this timescale, while the photos from Part 2 are from the lower end.

In the first major sequence below the Cambrian, there are finely layered strata containing something called dropstones.  These stones were somehow 'dropped' into the strata, causing interruptions or small deformations in the steady series of lines which indicate the layers of strata.  One way we know this can happen is through the movement of glaciers.  Glaciers will pick up material and, as they recede during a melt, will drop material, including rocks, into the mud it is leaving behind.  So when these dropstones were found in strata that deep, one of the first suspicions was perhaps a glacier did this.

Something else caused many to wonder about some kind of large glaciation all over the earth's surface when stones found in the Flinders Ranges north of Adelaide in South Australia showed up with paleomagnetic readings indicating they originated at the equator.  One would not suspect to find a lot of material which originated at the equator in South Australia.  Did ice do this?

The third bit of evidence that started some thinking very strongly about the possibility of an ice-covered world was finding something called 'diamictites' even below the sequences which contained the dropstones.  Diamictites are what we refer to as a cement-like matrix of material which contains rocks of all different sizes and shapes embedded within it.  "A debris layer" is a good description of the kind of material it reminds one of. 

The dropstones, the paleomagnetic indications, and the diamictites all together have given rise to a theory referred to as the "Snowball Earth" theory.  Knowing that there is almost nothing which could result in all three of these things showing up as we go through the layers of the earth, there has been a fairly strong case presented for the possibility that the entire earth was once covered in ice.  It would have to be the entire earth, for if there were glaciers at the equator which could recede to the south, carrying equatorial rocks to Australia, then there must have been glaciers everywhere.  What else besides glaciers could have done this?   There is something else, and that is what all this is about.

 

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