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> Theories still compete to some degree, but it is obvious there was a protective magnetic  shield early on, because we have evidence of very early life, that needed such protection:
> 
> https://www.sciencedaily.com/releases/2020/03/200315102257.htm
> 
> "A trio of studies are the latest developments in a paradigm shift that could change how Earth history is understood. They support an assertion by a geophysicist that a once-liquid portion of the lower mantle, rather than the core, could have exceeded the thresholds needed to create Earth's magnetic field during its early history. 
> 
> "In a study appearing March 15 in the journal Earth and Planetary Science Letters, Scripps Oceanography researchers Dave Stegman, Leah Ziegler, and Nicolas Blanc provide new estimates for the thermodynamics of magnetic field generation within the liquid portion of the early Earth's mantle and show how long that field was available.
> 
> "The paper provides a "door-opening opportunity" to resolve inconsistencies in the narrative of the planet's early days. Significantly, it coincides with two new studies from UCLA and Arizona State University geophysicists that expand on Stegman's concept and apply it in new ways.
> 
> "'Currently we have no grand unifying theory for how Earth has evolved thermally," Stegman said. "We don't have this conceptual framework for understanding the planet's evolution. This is one viable hypothesis."
> 
> ***
> 
> "'Ziegler and Stegman first proposed the idea of a silicate dynamo for the early Earth," said UCLA geophysicist Lars Stixrude. The idea was met with skepticism because their early results "showed that a silicate dynamo was only possible if the electrical conductivity of silicate liquid was remarkably high, much higher than had been measured in silicate liquids at low pressure and temperature."
> 
> "A team led by Stixrude used quantum-mechanical computations to predict the conductivity of silicate liquid at basal magma ocean conditions for the first time.
> 
> "According to Stixrude, "we found very large values of the electrical conductivity, large enough to sustain a silicate dynamo." 
> 
> ***
> 
> "If Stegman's premise is correct, it would mean the mantle could have provided the young planet's first magnetic shield against cosmic radiation. It could also underpin studies of how tectonics evolved on the planet later in history.
> 
> "'If the magnetic field was generated in the molten lower mantle above the core, then Earth had protection from the very beginning and that might have made life on Earth possible sooner," Stegman said.
> 
> "'Ultimately, our papers are complementary because they demonstrate that basal magma oceans are important to the evolution of terrestrial planets," said O'Rourke. "Earth's basal magma ocean has solidified but was key to the longevity of our magnetic field.'"
> 
> Comment: this study covers the earliest time of the Earth's existence in how a magnetic field was produced. Now the liquid iron-nickel core convection currents is thought to be the present provider. Special development of a special planet that supports life. By design.