We can learn a lot from studying the rings inside trees. The science of tree-ring analysis is called dendrochronology, and examining these markings can provide information about the tree’s age, whether it had been through any fires, or if it had endured any insect outbreaks. A tree’s rings can also give significant insight into what kind of climate conditions the tree has lived through, and thus how the earth’s climate has changed over time . Scientists have recently uncovered an ancient tree that lived during a time in Earth’s history when the magnetic field almost completely reversed .
The ancient tree is an Agathis australis, but is more commonly known by its Māori name, kauri. It was found in Ngawha on New Zealand’s north island and was buried 26 feet under the ground. Measuring eight feet in diameter and 65 feet in length, the tree appears to have lived for 1,500 years, between 41 thousand and 42 500 years ago .”There’s nothing like this anywhere in the world,” said Alan Hogg, from New Zealand’s University of Waikato. “This Ngāwhā kauri is unique.” 
What is Earth’s Magnetic Field?
The Earth has a solid inner core that is constantly transferring heat to its outer core, which is made of liquid iron. This causes the convection (or movement) of that iron. Since iron is a metal and therefore conducts electricity, it generates a magnetic field .
This magnetic field is very similar to the field that is produced by a common bar magnet. It is called a dipole because it has two poles at either end of the magnet. These endpoints are where the magnet is the strongest. You can picture the magnetic field like arched lines that leave the north pole and enter the south pole .
The Earth’s magnetic field aligns with its axis of rotation but is not stable over time. Periodically throughout geological history, the magnetic field decays and then becomes re-established, although scientists are still not sure why this happens. Whenever this does happen, it may return to its original state, or it may orient in the opposite direction, switching the north and south pole .
This pole reversal has happened periodically throughout Earth’s history, sometimes lasting for a few thousand years, sometimes for over thirty million years .
Why Does Earth Have a Magnetic Field?
Earth’s magnetic field is extremely important. The force it generates protects us from radiation in our solar system-, particularly from the sun. The sun releases vast quantities of radioactive particles into space, and it is our magnetic field that channels the particles away from the planet and preventing us from getting irradiated .