Quirks & Quarks

When the magnetic poles flip out, Earth seems to suffer

Magnetic pole reversal indicated in 42,000 year old tree rings may have triggered global environmental change

A magnetic reversal, when north and south poles switch, has been correlated with environmental change

Tree rings from the ancient Kauri tree in New Zealand showed a spike in radioactive carbon indicative of a magnetic pole reversal (Nelson Parker)

The Earth's magnetic poles have flipped many times in our planet's history - and while we know this is an important geophysical event, we haven't had any good evidence to indicate whether it's an important biological event. 

The last time the magnetic poles reversed permanently was nearly 800,000 years ago. The poles also flip more frequently on a temporary basis in what is called a magnetic excursion.

This means the reversal lasts up to a few thousand years before they change back. The last one of these is called the Laschamps excursion, and it happened nearly 42,000 years ago. 

A 'Hitchhiker's Guide' to magnetic pole reversal (UNSW)

A geological who-dun-it?

In a study, researchers including Chris Turney from The University of New South Wales, were able to use tree ring records to date a magnetic excursion correlate it with a series of environmental changes and extinctions that came about at the same time. This included the dramatic growth of ice sheets, changing wind patterns, a shift in the location of the Earth's tropical region, the extinction of some megafauna as well as the extinction of Neanderthals.

These types of changes have never been so closely correlated to the magnetic poles flipping before.

A kauri tree in New Zealand (Nelson Parker)

Ancient tree rings

The tree rings the team studied were from the ancient kauri trees in New Zealand. Remains of the massive trees were found preserved in nearly 10 metres of wetland soil. The rings of these trees indicate a massive spike in radioactive carbon in the atmosphere at the same time as the Laschamps excursion.

This is attributed to a reversal of the magnetic poles and subsequent weakening of the Earth's protective magnetic field. In the case of the magnetic excursion 42,000 years ago, that field was reduced to an estimated six per cent of what it is today. This meant that more radiation from outer space reached the atmosphere, changing the chemistry of the atmosphere and causing an increase in levels radioactive carbon.

This likely resulted in all of the global climate and environmental changes observed in other records at the same time. 

Trees rings reveal the date of the last magnetic pole reversal (UNSW)




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