EARTH
Earth's Magnetic Field
~3.9 billion years ago (claims reach 4.2 Ga)
The Earth's magnetic field, generated by currents of liquid iron in the outer core, has shielded the planet from the solar wind, charged particles emitted by the Sun, for about 3.9 billion years, or 4.2 billion according to some studies.
The Earth's magnetic field, also called the geomagnetic field, is generated in the outer core, the liquid layer of the Earth's core. Currents of liquid iron circulate there, and their motion converts mechanical energy, the energy of movement, into a magnetic field. This mechanism is called the geodynamo. The field extends far beyond the atmosphere. It deflects the solar wind. Without the field, the solar wind would strip the upper atmosphere away molecule by molecule. Mars lost its magnetic field early and retains only a thin atmosphere.
Why it matters
Mars has no magnetic field like the Earth's, and it has lost most of its atmosphere and nearly all of its water. The Earth has kept its atmosphere and its water. The difference follows largely from the Earth's core, where convection, the circulation of liquid iron driven by heat, has never stopped.
Dating & uncertaintyDisputed
Tarduno and colleagues (2015) interpreted magnetic grains enclosed in ancient crystals as a trace of the magnetic field 4.2 billion years ago. Tang and colleagues (2019) examined such grains by electron microscopy and maintain that every grain examined formed long after the crystal that encloses it. If so, the 2015 interpretation would be invalid. Tarduno and colleagues (2020) replied with new microscopy and dating measurements, and argue that some grains did form with their crystals. Crystals from Barberton, in South Africa, give a more secure trace of the field from about 3.9 billion years ago.
Earth history as one day
03:22:5920 h 37 min before midnight
if Earth’s 4.54 billion years were compressed into a single day