Teens

At the beginning of our solar system, when the planets were first born, Venus, Earth, and Mars were all very similar and all would have been able to support and form life. At that time the Sun was 30-40% cooler than it is now and so Venus (being closer to the Sun) would have probably been a more ideal place for life to form than Earth.

It is thought that the cause of Venus' greenhouse effect is its close proximity to the Sun, which caused the oceans to boil and evaporate as the Suns temperature rose, as well as the abundance of CO2 (carbon dioxide) in the atmosphere. This is thought to have happened within the first few hundred million years of Venus' history. The current surface on Venus is only 300-700 million years old (depending on the source; the planets are thought to be around 4.5 billion years old). This was caused by fissures opening all over the planet and covering the surface in lava (which makes Venus' surface about 85% volcanic rock; such a thing is possibly occurring now in Africa, though it's an extremely gradual process).

Earth and Venus are the two most similar planets in our solar system. Their masses, volumes, and densities are very similar. One major difference though is that a Venusian day is longer than a Venusian year (243 days and 224.7 days respectively). Also the pressure on Venus is about 90 times what it is on Earth (about the same as the pressure 1km underwater), while the gravity is 90% of Earths.

The temperature at Venus' surface is about 465°C while Earths is only 15°C (on average. The highest is 58°C and the lowest is -89.6°C). The Earths surface temperature has risen by about 0.5-0.9°C since the late 1800s and it's predicted that it could rise by 1.4-5.8°C by the year 2100.
Consider this: if the Earths temperature will rise by up to 5° in 100 years how long would it take to reach Venus' surface temperature? 8,900 years (based on Earths temperature rising by 5° every 100 years from 2100 and not taking into account that the higher the temperature the faster the temperature would increase).
So by the year 11,000 could the Earth look like Venus?

For how long was Venus inhabitable and how long would it take for life to evolve into humanoids?

Humans have been on the Earth just 2-5 million years, though apes have been here for 24 million. Life itself first developed around 3.5 billion years ago (as far as we know).
The oldest civilization, Mesopotamia (which includes the Babylonians and Sumerians among others), is only about 9,000 years old (although if you believe the Emerald Tablets of Thoth then the oldest could be Atlantis and over 56,000 years old).

The problem here is that Venus was volcanically resurfaced 300-700 million years ago, and during that time the most advanced life forms on Earth were reptiles, which first appeared about 325 million years ago. The first complex life forms, bilateral animals, appeared around 600 million years ago.

Still, there are many civilizations that have traditions of reptilian gods who came from the sky to form life on Earth. The Dogon of Mali tell of the Nommos, a race of reptilian/amphibious creatures who came from a planet said to revolve around a third star in the Sirius system (there are at present only two known stars in the Sirius system, however, the Dogon knew of the existence of Sirius B thousands of years before it was "discovered" by modern scientists).
The Sumerian gods are called the Nephilim, the Elohim, or the Annunaki which means "Those who from heaven came to Earth". The Sumerians believed these "gods" had come from a planet called Nibiru (the Assyrians and Babylonians called it Marduk).
There are also legends of amphibious gods who didn't necessarily originate in outer space such as the Chinese entity called Fuxi which is said to have the head of a man and the body of a fish. Fuxi is said to have lived around the year 3,322 BC.

But by looking at the facts it's probably safe to say that we're not Venusian. That doesn't mean that there couldn't have been earlier humanoid civilizations or tribes on Earth millions of years ago but it does seem unlikely. It also doesn't discount the fact that there could have been more recent visitors to this planet who've either chosen to stay or been stranded here (such as the Dropa). But anyway, who needs an alien civilization when the Ramas and Atlanteans had spaceships and atomic weapons?

Catalogue and Web Links:

Check out the books Venus Revealed and Lonely Planets by planetary scientist David Grinspoon.

And here I also have to give a special thanks to David Grinspoon. I sent him an early draft of this piece asking if all my facts were correct and if I'd missed anything. He was nice enough to reply and of course I had missed something (and when I read it I thought "duh") and so I thought rather than writing it into the article I'd include his reply here:

I enjoyed your piece. I agree with your conclusion that it is very unlikely that humans migrated from Venus. In addition to the geological facts which you summarize nicely, there is the fossil record on Earth, which shows convincingly that we come from a long line of Earthlings going back billions of years.
However, there is a way that we could still be Venusians that is consistent with all of that.
Since, as you point out, Earth and Venus were very similar when young, it is possible that life formed first on Venus. In addition we know that the planets, when young, were exchanging material all of the time because of the high rate of large meteor impacts, which blasted shrapnel between them. It is likely that bacteria could have stowed away on some of the rocks traveling between planets. So it is conceivable that the earliest life forms on Earth actually arrived here from Venus, in which case our very distant ancestors may have been Venusian.
Just a thought. Keep up the good work.

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Also while researching this article I came across a website called Class Brain which has a feature on it called Ask Class Brain!! So I decided to ask Class Brain, and this was my question:

Could the human race (or any species) have evolved faster under different conditions (eg. If the air was denser, water less abundant, etc?)?

The response I got was:

Although environmental conditions play a part in the process of evolution, they are not essentially what controls the rate of evolution.

Check out this article which supports the opinion that the brain of a species is what drives evolution . . .

And then two links to articles:
The Increasing Speed of Evoultion
A Speed Limit For Evolution

So while my question wasn't exactly answered I found this to be a really good system, I got quite a speedy response (only a few days), and I'll definitely consider using it again in the future.

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Another website I found really useful was Crystal Links, especially when researching the beliefs of early civilizations. My problem with the site is that sometimes it goes into stuff about reality being a grid pattern, etc... which I don't really believe. So it's a great site with lots of useful information, but be careful about what you do and don't believe.

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And also check out Science Direct which you can access by clicking on the mylibrary.info link at the bottom and then clicking on 'science'.