- 70% weaker in total(?) radiation - weaker at least in the visible by that much.
- higher activity in UV range
- spinning faster - like the Earth and the Moon, before they all traded rotation for distance.
- larger magnetic field - from the faster spin.
- bigger solar gamma and x-ray bursts - from the larger magnetic field.
- 6-12 hour rotation period - if you back up from current conditions of the Earth-Moon system, this is what you get for the time right after the Moon reformed after the impact of some Mars-size planetoid with the proto-Earth.
- 3x current heat flux from the interior due to more radioactives.
- thick atmosphere of CO2 (like Venus today) - there is a huge amount of CO2 buried today as rock formed by life.
- no oxygen, so no ozone to stop UV from reaching the surface - an incredible 10^30 more! That is a mind boggling amount of radiation, which the ozone layer currently keeps at bay.
- tides are 1000 times higher! (if moon is 10x closer)
- winds are very strong, east-west bands - due to rapid rotation.
- no large continents
- low levels of cloud cover -no nucleating particles.
- high level of infall of cometary organic material - inner solar system still full of debris
- much closer (10x closer?) - that is inside Earth's geosynchronous orbit. We have satellites that would have been further away!
- spinning itself - not yet tidally locked
- covering a huge piece of the sky - because of being so close
- collisions that make moons such as ours are rare but not completely unlikely - they might happen in 5-10% of solar systems with rocky planets
- 30 (out of 300) gas giant exoplanets discovered so far orbit in their star's 'habzone' - even if the planet is too big for life as we know it, it could have life bearing moons
Put some of these together, and you get a recipe for incredible weather. We often think of the ancient Earth as tropical volcanic islands being lapped gently by tides that swish warm and shallow waters of a lagoon containing a dilute organic soup.
Think again. Think howling winds blowing endlessly around the world, as they do between Antarctica and the southern continents. Think waves pushed by that wind and tides the size of the World Trade Center towers, rushing over flat landscapes to crash like tsunamis and run inland for miles, or entirely across the landscape to the next shoreline. Every 3 hours.
Think of the hurricanes. Clouds and rain nucleate around dust and organic chemicals floating in the sky. Not much of either would be available, so those heaving oceans just evaporate, and the amount of water in the atmosphere just keeps building up. And up. And up until it supersaturates. And then finally the rain starts to fall in huge fat drops. The storm grows, the quickly whirling planet triggers a spiral, an eye.
But there is no landfall to dissipate this hurricane. There is just the wind howling around the planet, and isolated islands being drowned by the tides. The hurricane could spin like Jupiter's Great Red Spot, around the world and then back over the same ocean that spawned it.
What are some of the Origin Of Life (OOL) implications?
High UV levels striking the ocean surface, where water and CO2 are present, can rapidly build many organic molecules. Some people fear that the UV would break big molecules apart faster than they could form. Luckily, that is not true. Long chain molecules, such as RNA, can 'quench' the high energy photon before it heats up the entire molecule, or breaks a single bond. The heat drains away into the ocean. So the high UV works in life's favor to build up lots of the chemicals of life.
Those winds? It turns out that the top layer of the ocean, a skin only a few millimeters thick, has its own dynamics. Evaporation raises the concentration of other chemicals just below the surface. And the wind whips the surface into masses of bubbles - spindrift. These bubbles trap chemicals together for long periods.
The tides? The endless pounding that landforms received was insurance that all kinds of useful chemicals were ground up and dissolved in the ocean, as rapidly as the volcanoes brought them to the surface.
It is also true that the endless cycling of tides and drying out is a natural form of what we call PCR - a way to duplicate organic molecules
No continents also meant that there was a much larger network of undersea cracks in the crust, where seawater and lava could meet. Today these conditions exist in fewer places, creating the 'black smokers' and 'lost cities' that support life without light. They would have been far more common in the ancient past.
Bottom line - as truly alien as our planet must have been three and a half billion years ago, it was still a setting in which life blossomed almost as soon as it was able. Some of the most important reasons are all based in the existence of the Moon as the large close companion of the Earth. Life may come up out of the depths, or at the surface, but the Moon donated the rocks and created the stirring motion of our oceans.