Ancient Rocks Hold Clues To How Earth Became A Habitable Planet And Avoided A Mars-Like Fate

According to a new study, the solid inner core of the Earth formed 550 million years ago and restored the magnetic field of the planet. This unravels how Earth became a habitable planet.

The scientists determined two new important dates in the history of Earth’s inner core by studying the magnetism locked in crystals. The dates are the time at which the magnetic field began to renew rapidly, and the time at which the growing inner core’s structure changed.

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Swirling liquid iron in the outer core of Earth creates the protective magnetic field around our planet. The iron flows approximately 1,800 miles beneath the surface of Earth. The invisible magnetic field protects the Earth from solar wind, and hence, is essential for the survival of life on the planet. Solar wind comprises streams of radiation from the Sun.

The strength of Earth’s magnetic field decreased to 10 per cent of its strength today, about 565 million years ago. Then, the magnetic field bounced back mysteriously, and regained its strength. This happened just before the Cambrian explosion, an event characterised by the unparalleled emergence of organisms between 541 million and 530 million years ago at the beginning of the Cambrian Period. About 20 to 35 major phyla, that make up modern animal life, emerged during the Cambrian explosion. According to a new study led by researchers at the University of Rochester, the solid inner core of the Earth formed 550 million years ago and restored the magnetic field of the planet.

The study describing the findings was published in the journal Nature Communications. 

How Did The Magnetic Field Of Earth Bounce Back?

The magnetic field rejuvenated within a few tens of millions of years, which is rapid on geological timescales. The bouncing back of the magnetic field coincided with the formation of the solid inner core of Earth. This suggests that the core is likely a direct cause of the rejuvenation, the study said.

In a statement released by University of Rochester, John Tarduno, one of the authors on the paper, said the inner core is “tremendously important”. He explained that right before the inner core started to grow, the magnetic field was at the point of collapse, but as soon as the inner core started to grow, the field was regenerated. 

The study authors have determined several important dates in the history of Earth’s inner core, including a more precise estimate for the age of the core. The study unravels several mysteries related to the history and future evolution of our planet, and how Earth became a habitable planet. The study also provides clues about the evolution of other planets in the solar system.

Layers Of Earth

The Earth is composed of different layers namely, the crust, the mantle, the molten outer core, and the solid inner core. The crust is the outermost layer, and the one where life is situated. The mantle is Earth’s thickest layer. The solid inner core is composed of an outermost inner core and innermost inner core. 

The diagram depicts Earth; first without an inner core, second, with an inner core that started to form 550 million years ago, and third, the formation of the innermost and outermost inner core 450 million years ago

Information Present Within Earth’s Ancient Rocks

The swirling liquid iron inside Earth’s molten outer core generates electric currents. This drives a phenomenon known as geodynamo which generates Earth’s magnetic field. Geodynamo is caused by electric fields generated in the same way as by the movement of an electric conductor in a magnetic field, and is driven by the thermal convection of the liquid iron inside the molten core. It is powered in part by the rotation of Earth. 

Since the magnetic field is related to the Earth’s core, scientists have been trying to figure out for decades how Earth’s magnetic field and core changed throughout our planet’s history. Due to the location and extreme temperatures of materials in the core, scientists cannot directly measure the magnetic field. 

According to the study, minerals that rise to the surface of the Earth contain tiny particles that provide information about the direction and intensity of the magnetic field at the time the minerals cool from their molten state. 

The study authors used a carbon dioxide laser and a superconducting quantum interference device (SQUID) magnetometer to better constrain the age and growth of Earth’s inner core. This is a very sensitive magnetometer used to measure extremely subtle magnetic fields, and consists of two superconductors separated by thin insulating layers. It can measure extremely weak signals, such as the electromagnetic energy field of the human body.

Using SQUID, the researchers analysed feldspar crystals from the rock anorthosite. According to Tarduno, the crystals have minute magnetic needles within them that are “perfect magnetic recorders”.

Important Dates In The History Of Earth’s Inner Core

The scientists determined two new important dates in the history of Earth’s inner core by studying the magnetism locked in crystals. The study of the record of Earth’s magnetic field in rocks, sediments or archaeological materials, which can lock-in a record of the intensity and direction of the magnetic field when they form is known as palaeomagnetism.

The two new important dates in the history of the inner core which the authors determined are the time at which the magnetic field began to renew rapidly, and the time at which the growing inner core’s structure changed.

The study found that 550 million years ago, the magnetic field began to renew rapidly after a near collapse 15 million years before that. The formation of a solid inner core resulted in the rapid renewal of the magnetic field, according to the study. The formation of the solid inner core recharged the molten outer core and restored the strength of the magnetic field, the authors noted in the study.

The researchers also found that 450 million years ago, the structure of the growing inner core changed, and this marked a boundary between the innermost and outermost inner core. Due to plate tectonics on the surface, changes took place in the structure of the mantle. The changes in the structure of the mantle coincided with the changes in the inner core. 

Tarduno said that because the researchers constrained the age of the inner core more correctly, they could explore the fact that the present-day inner core is actually composed of two parts. He added that plate tectonic movements on Earth’s surface indirectly affected the inner core, and the history of these movements is “imprinted deep within Earth in the structure of the inner core.

How Earth Avoided A Mars-Like Fate

Scientists have been able to uncover mysteries about Earth’s past and predict the planet’s future by understanding the dynamics and growth of the inner core and the magnetic field. They have also unravelled the ways in which other planets could generate magnetic fields and sustain the conditions essential to harbour life.

For instance, Mars once had a magnetic field, according to researchers. However, the field dissipated, and this left the planet vulnerable to solar wind and the surface of the Red Planet devoid of an ocean. 

According to Tarduno, Earth certainly would have lost much more water if our planet’s magnetic field had not been regenerated. He explained that Earth would be much drier and very different than the planet today.

He said the research highlights the importance of a magnetic shield and the need to have something like a growing inner core that sustains a magnetic field over the entire lifetime of a planet.