The Sun, Earth and Venus

[indepth]

So as our Sun gets older, it will get larger and hotter thus making life for us on Earth not so good, maybe similar to Venus? How do we know that Venus was not like Earth a few million-billion years ago and since then the Sun has grown hotter and larger making Venus unsustainable for life? Is there a way for us to know if the sun has gotten larger/hotter over its life?

 

[origin]

So as our Sun gets older, it will get larger and hotter thus making life for us on Earth not so good, maybe similar to Venus? How do we know that Venus was not like Earth a few million-billion years ago and since then the Sun has grown hotter and larger making Venus unsustainable for life? Is there a way for us to know if the sun has gotten larger/hotter over its life?

Wiki has a pretty good write up on the Sun. In a couple of billion years life on earth will probably not be possible due to the hotter sun. The Sun will be in the red giant stage in several billion years. In a million billion years the sun will be a small cool burnt out core of a star.

 

[indepth]

Thanks Origin

Could the Sun's 'habitable zone' have been at a different distance a few billion years ago than it is now?

 

[StarRider1701]

Thanks Origin

Could the Sun's 'habitable zone' have been at a different distance a few billion years ago than it is now?

Not likely. The sun is a very stable star which has remained and will remain pretty much the same for most of its life cycle. Very boring actually, with is exactly what is needed for life. No, it is not likely that Venus was ever habitable in the Earth sense. Will the Earth become like Venus a few billion years from now? Maybe, but I doubt the human race will have to worry about it much. We will either be long extinct or have long since moved elsewhere.

 

[MeteorWayne]

Sorry, that's not true. The solar output was about 30% lower 3.5 Gy ago, and continues to increase as the sun ages.

 

[JohnniG]

But isn't it true that the sun is relatively stable?

 

[MeteorWayne]

Yes, it is relatively stable. But it's output has been increasing for billions of years and will continue to do so until it doesn't anymore and head through the red giant and white dwarf part of it's lifetime.

 

[trumptor]

I would also like to know the opinion on whether Venus was Earth-like or not a billion or two years ago. Since we can calculate the energy output of the sun throughout its history, when was it that Venus began getting baked by the sun substantially more than we are today?

I find Venus fascinating because it is almost the same size as Earth and during the early days of the solar system I imagine Venus with oceans and maybe teeming with life that may have seeded the Earth with life in the distant past (probably not likely, considering life began on Earth almost as soon as it was possible).

Unfortunately even if there was any early life I doubt we would ever know. I think I read somewhere that the entire crust has been recycled by massive volcanic activity in the not too distant past.

And if only Mars had a magnetic field, I would assume in a couple of billion years Mars would be the preferred planet for life.

 

[Couerl]

I would also like to know the opinion on whether Venus was Earth-like or not a billion or two years ago. .

Well, Earth wasn't even "Earth-like" much more than 1/2 a billion years ago so I would say no. Earth was however, more Venus-like at least very early on and that is probably where the similarities end. It's true that bacterial life sprang up on Earth perhaps as far back as 3.5 billion years ago, but it wasn't until around 450 million yrs ago (2 bln yrs later) that something as simple as moss and lichens came along and so for a very long time the earth was for all practical purposes a hellish and deserted place. As funny as it sounds, something as simple as grass didn't even evolve until around 70 million years ago and didn't really take hold until 10 million years after the extinction of the dinosaurs..

 

[Gravity_Ray]

I would also like to know the opinion on whether Venus was Earth-like or not a billion or two years ago. Since we can calculate the energy output of the sun throughout its history, when was it that Venus began getting baked by the sun substantially more than we are today?

I find Venus fascinating because it is almost the same size as Earth and during the early days of the solar system I imagine Venus with oceans and maybe teeming with life that may have seeded the Earth with life in the distant past (probably not likely, considering life began on Earth almost as soon as it was possible).

Unfortunately even if there was any early life I doubt we would ever know. I think I read somewhere that the entire crust has been recycled by massive volcanic activity in the not too distant past.

And if only Mars had a magnetic field, I would assume in a couple of billion years Mars would be the preferred planet for life.

There is some evidence that Venus was Earth like several Billion years ago (it probably had Earth like Oceans) "Felsic highland crust on Venus suggested by Galileo Near-Infrared Mapping Spectrometer data.”

What happened to those oceans is not clear, but they probably evaporated as the temperature increased. Although Venus does "appear" Earth like it is not. For one thing because the planet doesn’t have a planetary magnetic field, its hydrogen has probably been swept into interplanetary space by solar wind. There is also no evidence of plate tectonics (probably because its crust is too strong to sub duct without water to make it less viscous). It appears to have volcanism but there are no lava flows, but its surface is very young, which may mean there are periods of catastrophic resurfacing that occur.

Basically this planet is nothing like Earth.

 

[MeteorWayne]

Recent evidence has emerged suggesting recent lava flows with potential ages from as much as a few million years to as little as 2500 years ago (Science, April 9)

 

[trumptor]

There is some evidence that Venus was Earth like several Billion years ago (it probably had Earth like Oceans) "Felsic highland crust on Venus suggested by Galileo Near-Infrared Mapping Spectrometer data.”

So if there were oceans back then, then wouldn't there have been enough water to lubricate the crust and mantle enough for plate tectonics to have existed. And wouldn't it have been possible back then for Venus to have still had a magnetic field? I don't see why this wouldn't be very possible along with the possiblity of this ancient environment to be a good location for the development of life.

 

[crazyeddie]

My understanding about the early history of Venus was that it's primordial environment was very similar to Earth's. In other words, it's atmosphere was rich in carbon dioxide and water vapor. Because the sun was dimmer and cooler soon after it formed, conditions on Venus may have been ideal for the formation of life. However, unlike the Earth, Venus had no moon to encourage tectonic activity, and a very slow (retrograde) rotation, and so it's iron core did not develop the conditions necessary to produce a strong magnetic field. The water vapor in Venus's atmosphere was quickly disassociated by solar radiation into hydrogen and oxygen, and was lost to space. Without plate tectonics to fix carbon dioxide into the crust and mantle of the planet, CO2 levels in the atmosphere increased due to volcanic outgassing, and a runaway greenhouse effect ensued. If life ever gained a foothold there, it did not last long.

 

[Gravity_Ray]

Eddy's explanation is very good. Also There is no denying the importance of our Moon for life on this planet. Starting from the impactor that probably tilted us for our seasons, to the current Moon that pulls and pushes the planets crust and causes the tides.

With out the Moon we would probably not be having this discussion right now.

 

[ExplorerAtHeart]

I would like to know why venus has such a slow backwards rotation.

Thats the #1 defect for Venus in terms of terraforming!

 

[crazyeddie]

I would like to know why venus has such a slow backwards rotation.

Thats the #1 defect for Venus in terms of terraforming!

There is speculation that, like the Earth, Venus was smacked by a large planetoid very early in the formation of the solar system. The object may have struck it in such a way that it robbed the planet of it's rotational angular momentum, and actually reversed it, so that it now rotates slowly in the opposite direction (retrograde). Earth's rotation, in way of contrast, is thought to have been speeded up by it's collision. The impact at Venus did not throw a huge amount of debris into orbit as it did with the Earth impact, and that's why Venus has no moon: there was nothing to coalesce.

 

[ExplorerAtHeart]

Thats a great theory!

(and to the OP WHODAT!)

 

[MeteorWayne]

There is also another theory that it's rotation was caused by resonances with it's orbit and Jupiter's. The current rotation is one of several that it could have wound up in.

 

[silylene]

I would also like to know the opinion on whether Venus was Earth-like or not a billion or two years ago. .

Well, Earth wasn't even "Earth-like" much more than 1/2 a billion years ago so I would say no. Earth was however, more Venus-like at least very early on and that is probably where the similarities end. It's true that bacterial life sprang up on Earth perhaps as far back as 3.5 billion years ago, but it wasn't until around 450 million yrs ago (2 bln yrs later) that something as simple as moss and lichens came along and so for a very long time the earth was for all practical purposes a hellish and deserted place. As funny as it sounds, something as simple as grass didn't even evolve until around 70 million years ago and didn't really take hold until 10 million years after the extinction of the dinosaurs..

Actually studies published in Science ~2005 showed that grass was already diversified and perhaps rather largespread in the Late Cretaceous (~70 M yrs ago). We know this because fossil grass phytoliths are commonly found in the coprolites of herbiverous dinosaurs from that era. [Previously, researchers had believed as you stated.]

Lichen is thought to have evolved about 600M years ago [researchers had previously thought 400M yrs ago, until new fossils were found.] http://www.china.org.cn/english/scitech/128654.htm

You are right on mosses, the earliest fossils known are about ~320 M years ago. But moss is a soft tissue plant, and earlier remains may not have fossilized often enough to have been found yet.

Theory dumped

The 65-67 million-year-old dung fossils, or coprolites, are thought to have been made by so-called titanosaur sauropods; large, vegetarian dinosaurs.

"It's difficult to tell how widespread [grass grazing] was," Ms Strömberg told the BBC News website, "Dinosaurs seem to have been indiscriminate feeders."

The study also sheds new light on the evolution of grass. Grasses are thought to have undergone a major diversification and geographic proliferation during the so-called Cenozoic, after the dinosaurs had gone extinct.

But the researchers found at least five different types of grass in the droppings.

This suggests grasses had already undergone substantial diversification in the Late Cretaceous, when the giant beasts still walked the Earth.
http://news.bbc.co.uk/2/hi/science/nature/4443696.stm

 

[ZenGalacticore]

For the record, the earliest origins of life on Earth, IIRC, has been pushed back to as early as 4.1 billion years ago. Super-primitive bacteria living deep under rocks, or something like that. (Which is pretty amazing.)

 

[Couerl]

Actually studies published in Science ~2005 showed that grass was already diversified and perhaps rather largespread in the Late Cretaceous (~70 M yrs ago).

Okay, okay, so when I was in college dinosaurs were still walking like the original Godzilla.. As kids those days we believed in anything. :geek: I just think it is very doubtful that Venus was ever "Earth-like" in terms of what we see around us today.. I do think though that if life ever came about on Venus or Mars that it is probably still there perhaps miles below their surfaces, just as it is here.. There is no reason to suppose it wouldn't be as surface conditions themselves would be largely irrelevant..