Determining the Age of a Sun

[Dryson]

I was wondering if anyone had any knowledge on how the age of a sun is determined?

The reason I ask is that if the age of an alien sun can be determined then the alien sun's age can be compared to our sun's. The ages of the two suns would then be compared with age of our sun to a time when dinosaurs roam the Earth.
If the alien sun is close to the same age as Earth then a planet with life on it might be present.
I would have to think that the same stellar material that Earth was made from would be closer to Earth than we think and not spread out all over the Universe.

 

[Christopher]

I was wondering if anyone had any knowledge on how the age of a sun is determined?

There are various different ways that are more or less reliable. Here are a couple of articles discussing the basics:

http://www.universetoday.com/25038/age-of-stars/

http://www.scientificamerican.com/article/how-do-scientists-determi/

The reason I ask is that if the age of an alien sun can be determined then the alien sun's age can be compared to our sun's. The ages of the two suns would then be compared with age of our sun to a time when dinosaurs roam the Earth.
If the alien sun is close to the same age as Earth then a planet with life on it might be present.

The age of dinosaurs isn't really a good comparison point for that. The Sun formed 4.5 billion years ago (4,500,000,000). Single-celled life emerged about 4 billion years ago. It took another 3.5 billion years until multi-celled life finally emerged, say 450 million years ago, when the Sun was roughly 90 percent of its current age. The dinosaurs first evolved about 230 million years ago, when the Sun was about 95 percent of its current age, and they died out when the Sun was about 98.5% of its current age.

There's a good chance that single-celled life could exist anyplace where there's liquid water, organic molecules, and heat. Most stars that are on the main sequence and that have planets (which we now believe most stars do) may well have microbial life. Multicellular life, though, is less of a sure thing. There's no reason to expect that life on another world would develop at the same rate that it did on Earth. It took a very, very long time on Earth before the right set of random mutations occurred to allow sexual reproduction to arise and speed the pace of evolution, which then led to multicellular life and everything else since. Since it's random, on another world that mutation might take twice as long to arise, or half as long. The same for the origin of single-celled life itself. Since we only have one example of the evolution of a biosphere, our own, we have no way of judging how typical or atypical its development was. Back when our own planetary system was the only one we knew of, we assumed that most other planetary systems would be structured like it. Now we've found hundreds of extrasolar planetary systems and we know they come in many forms that are wildly different from ours. Assuming that we are the template for the whole universe is nothing more than arrogance.

I would have to think that the same stellar material that Earth was made from would be closer to Earth than we think and not spread out all over the Universe.

Not really. The Sun has been orbiting the center of the galaxy for 4.5 billion years, and since it takes about 225 million years (give or take) to complete an orbit, that means it's circled the whole galaxy somewhere around 20 times in its lifetime. And all the millions of stars it's passed have exerted their own gravitational pulls and churned things up, not to mention all the interstellar gas and dust clouds along the way. The material from the stellar nursery in which the Sun and its sibling stars formed, not to mention those other stars themselves, would have been scattered so thoroughly around the galactic disk by now that there's no way to track them down.

 

[Asbo Zaprudder]

A potential sibling star (HD 162826) to the Sun is located 110 ly away:

Astronomers Find a Sibling Star to the Sun

However, it's not an exact twin of the Sun. As it's 15% more massive, it ages more rapidly with an expected Main Sequence lifespan of 7 billion years against 10 billion years for the Sun.

 

[Dryson]

The dinosaurs first evolved about 230 million years ago, when the Sun was about 95 percent of its current age, and they died out when the Sun was about 98.5% of its current age.

If dinosaurs evolved at 95% of the suns age of then by calculating a targeted sun that is about 95% its age as well and is similar to our own sun is then based on the evolution of Earth a planet orbiting a 95% aged sun might be more likely to have life evolving on it if the planet resides within the goldilocks zone.

 

[sojourner]

Math bad.

 

[Christopher]

If dinosaurs evolved at 95% of the suns age of then by calculating a targeted sun that is about 95% its age as well and is similar to our own sun is then based on the evolution of Earth a planet orbiting a 95% aged sun might be more likely to have life evolving on it if the planet resides within the goldilocks zone.

Your statement makes no sense. I said the dinosaurs evolved when the Sun was at 95% of its current age, not its total life expectancy. Its current age is less than half its expected main-sequence lifespan. By definition, every star is currently at 100% of its current age, but of course they're all at wildly different percentages of their life expectancies.

And you're still making the completely illegitimate assumption that other planets' development would somehow magically happen on the exact same schedule as it did on Earth. I explained why it makes no sense at all to assume that. It could happen far faster or far slower. Yes, the older a main-sequence star is, the higher the probability that its planets have evolved life -- but by that very argument, using Earth as a benchmark is a bad idea, because our Sun is less than halfway through its lifespan, and that lifespan is only moderate. By the probabilistic argument, the best places to look would be around red dwarf stars, which are much smaller and cooler than our Sun and therefore can be much longer-lived. There are plenty of stars out there much older than the Sun, and they've had a lot more time for life to evolve. So they're better places to look than stars of the Sun's relatively young age.

I also don't know why you insist on using the dinosaurs as a benchmark. They're not the only organisms that existed in Earth's prehistory, just the most heavily hyped ones. Granted, their evolution was about halfway through the history of multicellular, land-dwelling life, so that might actually work as a median of sorts. But the history of multicellular life is about 1/8 of the total history of life on the planet. The other 7/8 was all single-celled organisms or colonies thereof.

 

[Doom Shepherd]

Yep, we don't even know for sure what caused all the mass extinction events in Earth's history, and if a planet that started out at exactly the same time avoided some or all of them (or had more of them), that alone could totally alter the timescale of life's development - and that's only one of who knows how many factors.

There's absolutely NO reason to think that life on any planet other than ours has to go through some kind of "natural" trilobite-to-fish-to-amphibian-to-reptile-to-dinosaur-to-mammal-to-intelligence cycle. For all we know it could avoid mass extinctions and take half the time to go from trilobite-to-super-trilobite-to-trilobite-sapiens-to-Shadow or something.

 

[Asbo Zaprudder]

Just to avoid certain people being mislead...

Fish (which are deuterostomes, as are all vertebrates) did not evolve from trilobites (which were protostomes) and mammals did not evolve from dinosaurs. Animals similar to Metaspriggina or Pikaia and the Synapsids or Therapsids respectively would be better ancestor candidates respectively. I'd avoid the word "cycle", which might be taken to imply that mammals will revert to trilobytes at some stage. Otherwise, I sense a bad episode of Star Trek: Voyager coming on...

 

[Christopher]

For all we know it could avoid mass extinctions and take half the time to go from trilobite-to-super-trilobite-to-trilobite-sapiens-to-Shadow or something.

If anything, it'd be the other way around. It's been argued that mass extinctions actually promote evolution rather than inhibiting it. Not only do they create new survival challenges that life has to adapt to, but they open up environmental niches for species to evolve into, so they create new opportunities for evolution to happen. And reducing a species' population to a small number increases the probability that a new mutation can survive and spread, because it'll be up against less competition, so statistically speaking, it's less likely to be crowded out of the gene pool. Indeed, the evolution of hominids seems to have been jumpstarted by a partial mass extinction caused by a nearby supernova a couple of million years ago.

So a planet in a quieter part of the galaxy, one that was subjected to less frequent mass extinctions, would have less pressure on its biosphere to evolve and adapt, and would probably have much slower evolution. After all, evolution isn't some inevitable forward progression built into our genes, like fiction tends to misrepresent it as. It's a process by which organisms adapt to environmental change. Thus, the rate of evolution is linked to the rate of environmental change. The more the environment changes, the more life evolves. Sure, there's probably a point at which the stress of constant global extinctions becomes too much for life to rebound from, but in general, a more turbulent planetary environment would promote faster evolution.

And of course evolution isn't some inevitably "upward" progression like your examples suggest. There's no direction to it, beyond the selection for a greater ability to survive in a given environment long enough to reproduce. True, there is a theory that thermodynamic forces tend to promote the rise of intelligence because it allows the creation of more future possibilities and thereby increases causal entropy, and that there's a "cognitive niche" in evolution because intelligence and tool use create new possibilities for adaptation beyond what genetic evolution is capable of by itself. But evolution isn't a ladder. Intelligent life forms are just one branch (or a few branches) on a huge, ever-growing tree, the vast majority of whose branches are microorganisms and plants and insects. Intelligence is one survival adaptation out of many, not an ultimate end goal of the evolutionary process.

 

[Doom Shepherd]

If anything, it'd be the other way around. It's been argued that mass extinctions actually promote evolution rather than inhibiting it. Not only do they create new survival challenges that life has to adapt to, but they open up environmental niches for species to evolve into, so they create new opportunities for evolution to happen. And reducing a species' population to a small number increases the probability that a new mutation can survive and spread, because it'll be up against less competition, so statistically speaking, it's less likely to be crowded out of the gene pool. Indeed, the evolution of hominids seems to have been jumpstarted by a partial mass extinction caused by a nearby supernova a couple of million years ago.

So a planet in a quieter part of the galaxy, one that was subjected to less frequent mass extinctions, would have less pressure on its biosphere to evolve and adapt, and would probably have much slower evolution. After all, evolution isn't some inevitable forward progression built into our genes, like fiction tends to misrepresent it as. It's a process by which organisms adapt to environmental change. Thus, the rate of evolution is linked to the rate of environmental change. The more the environment changes, the more life evolves. Sure, there's probably a point at which the stress of constant global extinctions becomes too much for life to rebound from, but in general, a more turbulent planetary environment would promote faster evolution.

And of course evolution isn't some inevitably "upward" progression like your examples suggest. There's no direction to it, beyond the selection for a greater ability to survive in a given environment long enough to reproduce. True, there is a theory that thermodynamic forces tend to promote the rise of intelligence because it allows the creation of more future possibilities and thereby increases causal entropy, and that there's a "cognitive niche" in evolution because intelligence and tool use create new possibilities for adaptation beyond what genetic evolution is capable of by itself. But evolution isn't a ladder. Intelligent life forms are just one branch (or a few branches) on a huge, ever-growing tree, the vast majority of whose branches are microorganisms and plants and insects. Intelligence is one survival adaptation out of many, not an ultimate end goal of the evolutionary process.

All good points.

 

[publiusr]

Agreed. Then too--I wonder what life might have looked like had Earth kept its maximum level of oxygen--around 35% towards the end of the Carboniferous period (about 300 million years ago)....as per the wiki

https://en.wikipedia.org/wiki/Great_Oxygenation_Event
http://www.nap.edu/read/11630/chapter/4#37

Sadly, oxygen and water are two of the substances that are the most damaging to DNA: https://www.nobelprize.org/nobel_prizes/chemistry/laureates/2015/press.html

It doesn't take much. I guess all those CO2 breathers early on had it right all along. While we need oxygen to breathe, it wears at us over time. The mammalian heart is like a big block Chevy engine with blowers. It takes a lot to keep us warm-bloods alive.