According to a new NASA study, powerful solar storms could have been instrumental in warming ancient Earth, and preparing the planet for the development of complex life. Known as "superflares," the space weather events were thought to be roughly 10 times more powerful than any solar storm that has struck Earth since the advent of modern civilization.
Astronomers are able to piece together the history of our Sun by analyzing similar main sequence stars in the various stages of their evolutionary cycle, through powerful telescopes such as Hubble and Kepler.
From these observations we can tell that around 4 billion years ago when life first began, the Sun shone only two thirds as bright, and provided only 70 percent of the energy as it does today. These stellar conditions should have rendered Earth an icy, inhospitable world, yet we know from geological records that this was not the case.
New research suggests that our planet and the Sun boasted complementary traits that allowed early life to be nurtured and incubated even as the two celestial bodies matured. Current-day Earth generates a strong magnetic field capable of deflecting the majority of the stellar material flung at it through events such as a coronal mass ejections.
However, 4 billion years ago Earth's magnetic field was much weaker, especially around the polar regions. At the same time, while the overall output of our Sun was lower than it is today, observations made by Kepler of Sun-like stars of an age with ancient Earth suggests that it generated powerful solar storms known as superflares on a regular basis.
Energetic particles from the superflares may have traveled down magnetic field lines, entering Earth's atmosphere through the polar regions. Once in Earth's atmosphere, the stellar particles broke down nitrogen molecules creating vast quantities of free-floating nitrogen particles, which combined with oxygen to form nitrous oxide.
Nitrous oxide is a powerful greenhouse gas up to 300 times more effective as an atmospheric warming catalyst than carbon dioxide. A relatively tiny amount of nitrous oxide could have trapped enough of the Sun's energy inside ancient Earth's atmosphere to create warm surface conditions favourable to the evolution of life.
The energy provided by the charged particles may have provided the boost needed for simple molecules to combine to form complex molecules such as DNA and RNA. Insights into how Earth became an ideal breeding ground for life will directly aid the search for its extraterrestrial counterpart.
Astronomers can now search for Earth-like planets with relatively weak magnetic fields orbiting in the habitable zone of stars exhibiting superflares, in the knowledge that these are promising signs of a young world capable of playing host to life.