When was the first sunrise on Earth?
Eric Kvaalen
Les Essarts-le-Roi, France
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That is simply a question of how you define 鈥�Earth鈥�. Assuming that our planet came together gradually as dust and particles slowly agglomerated, at what point do we start calling a particular chunk 鈥淓arth鈥�?
Maybe we should say it was the first chunk that was bigger than anything that subsequently fell onto it. In any case, it was always rotating, so as soon as we can call it Earth, the first sunrise on Earth occurred.
Hillary Shaw
Newport, Shropshire, UK
For a sunrise, you need a transparent atmosphere and a solid or liquid surface. Earth probably acquired these at the end of the Hadean Aeon, just after the Late Heavy Bombardment, when dust began to clear from the atmosphere. This was 4 billion years, or some 1.5 trillion sunrises, ago, even allowing for the shorter days then. Early in Earth鈥檚 history, days were just 17 hours long due to tidal effects.
Within another 1.3 trillion sunrises, the sun will go nova. If this doesn鈥檛 vaporise Earth, it will melt the surface and, for a while, the 鈥渁tmosphere鈥� may go opaque again as the planet becomes a sea of boiling lava.
However, our sun will then become a white dwarf and the scorched cinder of our world will experience some 4 quadrillion more sunrises before the intense, brilliant point of white light that the sun has become finally cools to blackness.
Garry Trethewey
Arkaroola, South Australia
Assuming the sun had ignited, the first sunrise on Earth was the first day that the planet existed. Then the question becomes something like: 鈥淲hen did all the material that was to become Earth actually become Earth?鈥� or 鈥淗ow do we define a boundary between a proto-Earth and Earth?鈥�
I don鈥檛 suppose a rotating gas ball can really be called Earth. At some stage, it would have condensed enough to form solids and liquids and would be big enough to be round.
Perhaps that was the first day Earth existed.
Malcolm Campbell
Brisbane, Australia
Earth鈥檚 early atmosphere was opaque because of the formation process of the planet (which involved volcanic activity and impacts from asteroids and comets). The light from the young sun wouldn鈥檛 have been able to reach Earth鈥檚 surface, so the 鈥渇irst sunrise on Earth鈥� wouldn鈥檛 have happened until the atmosphere cleared.
While it is difficult to determine the exact moment when the atmosphere cleared enough for sunlight to reach the surface, the gradual rise of oxygen during the Great Oxidation Event, which occurred 2.4 billion to 2.1 billion years ago, played a crucial role in allowing sunlight to penetrate the atmosphere.
Over time, various geological and biological processes, such as volcanic activity and the emergence of photosynthetic organisms like cyanobacteria, contributed to transforming the atmosphere. Through photosynthesis, the organisms produced oxygen as a by-product, leading to its gradual build-up in the atmosphere.
So, the first sunrise on Earth would have happened around the time of the Great Oxidation Event.
Richard D. Cooper
via Twitter
It鈥檚 in my diary: On this day, 4.543 billion years ago, first sunrise. Think it was Tuesday.
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