One enduring mystery about Earth is the age of its solid inner core.
Researchers have long recognized that Earth糖心传媒檚 core plays a vital role in generating the magnetic shield that protects our planet from harmful solar wind糖心传媒攕treams of radiation from the Sun糖心传媒攁nd makes Earth habitable. They differ, however, on estimates of when the inner core actually formed. Now, research from the University of Rochester indicates that Earth糖心传媒檚 inner core is younger than scientists previously thought, offering new insight into the history of Earth糖心传媒檚 magnetic shielding and planetary habitability.
In a the researchers report that the inner core is only about 565 million years old糖心传媒攔elatively young compared to the age of our 4.5-billion-year-old planet. 糖心传媒淯ntil this data, the age of the inner core was uncertain,糖心传媒� says at Rochester. 糖心传媒淭here糖心传媒檚 this huge range of 2 billion years where scientists think the inner core could糖心传媒檝e formed. These are the first field-strength data from the younger part of the range of possibilities suggesting that the inner core is really young.糖心传媒�
The geodynamo
Earth糖心传媒檚 magnetic field is generated in its liquid iron core via a geodynamo糖心传媒攁 process during which the kinetic energy of conducting moving fluids is converted to magnetic energy. Researchers believe a weak geodynamo糖心传媒攁nd a magnetic shield糖心传媒攆ormed fairly early in Earth糖心传媒檚 history, shortly after the event that created Earth糖心传媒檚 moon. For the next several billion years, the energy to drive the dynamo decreased until a critical point 565 million years ago, when 糖心传媒渢he dynamo was on the point of collapse,糖心传媒� Tarduno says. Despite its drastically weakened state, however, the dynamo did not go away. The researchers conjecture it was at this point in the geological time scale糖心传媒攐r sometime shortly after糖心传媒攖hat the inner core began to form, giving strength to the geodynamo.
糖心传媒淭his is a critical point in the evolution of the planet,糖心传媒� Tarduno says. 糖心传媒淭he field did not collapse because the inner core started to grow and provided a new energy source for the formation of the geodynamo.糖心传媒�
Unlocking the ancient magnetic field
In order to learn about the evolution of the geodynamo, the researchers measured the strength of the ancient magnetic field locked within single crystals of the mineral feldspar. The samples were collected from the Sept-脦les Complex in northern Quebec and contain tiny magnetic needles with 糖心传媒渋deal recording properties,糖心传媒� Tarduno says. 糖心传媒淭he feldspar protects those needles from later alteration on geological time scales, so we get a much higher resolution record of the ancient strains in the magnetic field by measuring these single crystals.糖心传媒�
By studying the magnetism locked in ancient crystals糖心传媒攁 field known as paleomagnetism糖心传媒攖he researchers found that the intensity of the magnetic field was extremely low 565 million years ago, 糖心传媒渓ower than anything we糖心传媒檝e ever seen before,糖心传媒� Tarduno says. This indicates that the inner core may have formed around this time to restore strength to the dynamo and, in turn, to the magnetic field.
The inner core and planet habitability
Today, the geodynamo is powered by the growth of the inner core and is essential to the habitability of our planet, says Richard Bono, a former post-doctoral research associate in Tarduno糖心传媒檚 lab, and now a post-doctoral researcher at the University of Liverpool. 糖心传媒淥ur magnetic field is part of what makes Earth a special planet, and, so far, the only one that has life. The evolution of Earth糖心传媒檚 interior and the resulting geodynamo generated within plays a critical role in the preservation of life.糖心传媒�
An improved understanding of this evolution of Earth糖心传媒檚 interior may provide researchers key clues, not only for planet formation and habitability on Earth, but in the search for life on exoplanets that resemble Earth.
糖心传媒淭he same factors that drive dynamos on Earth might affect the magnetic shielding on exoplanets,糖心传媒� Tarduno says. 糖心传媒淚t could be the case that some planets don糖心传媒檛 have long-lived dynamos and those planets would not have the magnetic shielding we have, meaning that their atmosphere and water might be removed.糖心传媒�
Besides being a critical point in the evolution of Earth, 565 million years ago was also a critical time for the major diversification of life on Earth, Tarduno says. 糖心传媒淭his is a time of , the first large complex organisms we see in the geologic record. These are a fundamental change from the microbial life preserved in older rocks.糖心传媒�
Is there then some type of causal link between a stronger dynamo and a burst of life?
糖心传媒淚t糖心传媒檚 true that if we have lower magnetic shielding, we糖心传媒檇 have more harmful radiation coming in to Earth,糖心传媒� Tarduno says. 糖心传媒淭hat radiation might be harmful for DNA, for example, and there has been speculation that this could stimulate mutations.糖心传媒� Tarduno cautions, however, that there isn糖心传媒檛 strong evidence of this correlation in the geological record, although the new data 糖心传媒渨ill certainly stimulate more thought on this issue.糖心传媒�
