New Evidence Puts Snowball Earth Theory Out In The Cold.

Byline: Staff Writers

LONDON, UK, March 26 (SPX) -- The theory that Earth once underwent a prolonged time of extreme global freezing has been dealt a blow by new evidence that periods of warmth occurred during this so-called 'Snowball Earth' era.

Analyses of glacial sedimentary rocks in Oman, published online today in Geology, have produced clear evidence of hot-cold cycles in the Cryogenian period, roughly 850-544 million years ago. The UK-Swiss team claims that this evidence undermines hypotheses of an ice age so severe that Earth's oceans completely froze over.

Using a technique known as the chemical index of alteration, the team examined the chemical and mineral composition of sedimentary rocks to search for evidence of any climatic changes. A high index of alteration would indicate high rates of chemical weathering of contemporary land surfaces, which causes rocks to quickly decompose and is enhanced by humid or warm conditions. Conversely, a low chemical index of alteration would indicate low rates of chemical weathering during cool, dry conditions.

The researchers found three intervals with evidence for extremely low rates of chemical weathering, indicating pulses of cold climate. However these intervals alternate with periods of high rates of chemical weathering, likely to represent interglacial periods with warmer climates.