by Matthew Cobb
Following on from our discussion about what life might like to do with the remaining 20% of its time on Earth (ie 1 billion years before the sun makes it too darn hot), this excellent video by Claire L. Evans shows the history of the planet in 60 seconds. I show this to my first year students every year, as it gives a real impression of the importance of that long period when life was busy being only unicellular, inventing photosynthesis, setting up symbiotic relationships with smaller energy-generating cells (ciao Lynn Margulis!) – that kind of thing. And then everything went mental in the last 5-6 seconds (sorry if that was a spoiler for anyone). Now all you have to do is imagine how that recent exuberance would continue for another 15 seconds or so…
NB It is of course ‘last banded iron formations’ not ‘ion formations’…
Another typo is “Panagea” for “Pangaea”
It is astonishing how quickly life evolved after the earth stabilized.
I mean, how quickly life emerged…I guess it didn’t do much macroscopic evolving until later.
I see three stages of life evolution.
Primitive / unicellular life forms are very quick to emerge, more complex life are much later. Then the consciousness mind much much later.
Each stage moving down on probability scale, but move up on speed of changes (and complexity).
Primitive lifeforms maybe a certainty for a earthlike planet. Plants and animal not very probable. Conscious mind least probable.
Then the speed of change.
Historically, what happens now are very hectic. What next is something new, explosion and extinction? Maybe most complex lifeforms ended that way?
It is interesting to know that by looking at the pace of the clock, that may be we see the end of earth in our lifetime (very jesus-like talk .. :D)
One way or another.
At least you didn’t vouch for a ladder of descent. As for acquiring traits, the first populations likely didn’t have many which obviously makes for species with more.
If by “primitive” you mean ancestral, that is how phylogenies goes.
As for complexity there are many measures.
– Prokaryotes can be multicellular with differentiated cells (say, for spore bodies), and NASA Astrobiology site claims that it has happened independently ~ 30 times. [I can’t find the ref right now.]
Certainly cyanobacteria, which can have differentiated cells of many types, evolved early. Earliest finds of stromatolites that have macro- and micro-characteristics compatible with cyanobacteria are ~ 3.5 Ma bp.
– Some ~ 6 multicellular lineages evolved what NASA called “complex multicellularity”, with more multicellular traits. Those evolved out of eukaryotes, which have access to ~ 10^5 times as much energy for protein turnover due to mitochondria endosymbiosis (Lane’s energy hypothesis). Consequently eukaryotes can be expected to be able to manage more traits.
– Unicellular eukaryotes can have larger genomes than multicellular. The largest known protozoan gene number is 4 times larger than in humans.
As for consciousness there is no clear definition.
– Many species pass the mirror test for self recognition.
– Models of cortex, an ancestral trait that have homologous structures in vertebrates and invertebrates (“mushroom bodies”), shows that symbol like learning self organizes. Symbol formation avoids the over-training phenomena in other types of neural nets, which is likely why it survived.
Since the template for symbolic thinking is present in very primitive neural systems, it shouldn’t be surprising that it emerges in learning tasks such as vocalization IMHO.
– Since mass extinction events has allowed land life to recapture diversity 3 times, a simple estimate would be that ~ 2/3 of independent diversifications leads to social intelligence such as in humans.
To summarize, I don’t think consciousness is all that special. Eukaryotes with mitochondrial endosymbionts likely evolved immediately after the atmosphere became oxygenated enough that it was a fitness advantage. (Recently sequenced Megavirus seems evolved by parasitic loss from an ancestral eukaryote that had phagocytosis, which the parasites depend on, and endomembranes but no mitochondrion.)
Then the mitochondrion could have acted as a frozen accident, preventing similar events among eukaryotes but also prokaryotes by competing with phagocytosis traits. (Some bacterial planctomycetes have endocytosis but not phagocytosis.)
To summarize, I don’t think it is particularly obvious that multicellularity et cetera are especially rare. Oxygenation, the crucial event, depended on prolonged plate tectonics which seems easy enough in superEarths. It is Earth that is marginal in that sense.
All other environmental factors for planets seems fairly likely as well; large moon creating impact events happen often (Moon-Earth, Pluto-Charon) so spin axis stabilization happens often; magnetic fields are unnecessary but also likely not rare for superEarths; et cetera.
Of course the current show of individuality in exoplanet systems means that the number of suitable Earth analogs partition to a relatively small number.
Only one factor is Goldilocks for Earth, and ties in to its marginal plate tectonics: the amount of ocean water. To have oceans but also land means having ~ 0.0005 of mass as water (half goes into the crust). A factor 5-10 means either a dry or a water planet.
Likely no high technology civilization for those outside the water Goldilocks domain.
if my first comment comes out of moderation, it has several shortcomings:
– multiple HTML fail (but correct links).
– multiple summaries. :-/
– Earth water content is ~ 0.005 by mass (not 0.0005).
So much for a lucid presentation. I plead lack of coffee.
Where does it show the de novo mutation that resulted in Rick Santorum?
Or Ken Ham.
Santorum is a mystery that simply cannot be explained.
Therefore Satan!
God did it. Duh!
I kept waiting for the Cambrian explosion, knowing full well that it wouldn’t happen until about 6 seconds left, but it still shocked me how long it took for it to happen. This video really brings home the time scales involved.
I can’t help thinking that the vast majority of planets with life on them will simply be covered in bacteria. Anything more seems very unlikely.
To say that life on Earth is 80% through it’s allotted time slot severely misrepresents the magnitude of evolutionary possibilities.
At the rate things are going, a lot could happen in a billion years.
As for what is to come in the next few 100s of millions of years:
<a href="http://www.youtube.com/watch?v=NYbTNFN3NBo&feature=related" http://www.youtube.com/watch?v=NYbTNFN3NBo&feature=related
I note the eternal home and promised land of the Abramamic god didn’t exist 50 million years ago, and will not exist 50 million years in the future.
When you think about it, the holy myths of the region are based on a static, built from the top down world. We now know the world is built bottom up, and dynamic.
argh. html fail again. I blame a lack of preview. anyway, the link still works.
Wait, what? “Only” one billion years before Earth dies? I stupidly thought that life would last until the total destruction of the planet, 5 billion years from now. Quick, build a space ark, and find a new planet! Our tree of life must continue to grow forever among the stars!
The sums are a bit dodgy in detail because of the multiple interacting positive and negative feedback loops (i.e. climate), but the basic idea is that, as the sun steadily increases in luminosity (because of the increasing amount of helium “ash” in it’s core), then temperatures on Earth will also, slowly, increase. To a degree this can be countered by the activities of life (Dawkins’ “Daisy World” simulations, for example [Hmmm, more references there to Lovelock than Dawkins, but I thought it was Dawkins’ idea. Whatever ; one or the other.]), but at some point the temperature will become high enough that water vapour in the atmosphere will increase to the point that the greenhouse gas effect of the …
(Oh, yeuch, Stephen Fry has just given the worst definition of a “black body” that I’ve every heard. “Quite Interesting” is, for once, Quite Wrong. Or his script-writers botched the job of explaining it … General Ignorance indeed. [Wince!])
Where was I? … water itself is a significant greenhouse gas, and eventually it will get to the point that a positive feedback between temperature, atmospheric water vapour, greenhouse effect and temperature again will rapidly ( a few million years) boil the oceans.
At which point, bye-bye weathering and no way out. Or to put it another way : [music, Maestro, please] “Hello Venus my old friend / I’ve come to talk to you again …”
Exactly at what point in the Sun’s future that is going to happen is a bit unclear, but it’ll be well before the Sun goes red giant and (possibly) envelops the Earth-Moon double planet.
I haven’t heard any serious climate researchers suggest that the present bout of global warming is likely to accelerate into a case of Venus Syndrome.
Life developed quickly? I don’t think so. People just have a hard time processing the amount “millions” of years.