The data as I understand it does suggest that the Earth ~ 3.5Bya was comparatively warm. This is somewhat puzzling since the sun was likely about 25-20% cooler then. I suspect the solar system was in a different configuration then, though not drastically so. The Earth may well have been in a closer orbit to the sun. The solar system is not completely stable, and it might be wrong to suppose it had the same configuratio then that it does now.

Lawrence B. Crowell

It has interesting consequences for biosphere lifetimes though, when comparing tectonic biospheres vs others, or considering the future development of galactic habitable zones.

extremophile species of prokaryotes.

Those are the same as archaebacteria AFAIU. Bacteria can take 70-80 Celsius, at least it's a constraint for their oxygenic photosynthesis, and according to protein and DNA fold data had such a bottleneck in precambrian times. This correlates with the temperature data on cherts harking back 3.5 Ga.

[I'm not the only one noticing this. James Kasting spoke of this at the STScI -09 May symposium:

Climate on the early Earth remains an enigma, as well. Despite the faintness of the young Sun, the early Earth appears to have been warm, or perhaps even hot. Taken at face value, oxygen and silicon isotopes in ancient cherts imply a mean surface temperature of 70(+/-15)oC at 3.3 Ga. A recently published analysis of the thermal stability of ancient proteins supports this conclusion. This evidence for hot early surface temperatures must be weighed against theoretical considerations, as well as geomorphic evidence for glaciation at 2.9 Ga, 2.4 Ga, and 0.6-0.7 Ga. Such models must also account for the well documented correlation between the rise of O2 at 2.4 Ga and the Paleoproterozoic glaciations which occurred at that same time.

(I'm not as convinced of global or even local glaciations as Kasting.)

According to the two isotope thermometers of cherts (and correlating with the two of proteins and DNA), sea temperatures linearly decreased from ~ 80 to ~ 20 Celsius at the start of the Cambrian.

Also, while abiogenesis probably occurred in alkaline heat vents driven by redox potentials of circulating acidic sea water, it seems from the same data that the first proteins developed at moderate temperatures ~ 20 Celsius. Probably life developed before the late heavy bombardment originated the later green house carbon dioxide atmosphere. And now there is a paper showing that life probably can survive LHB.]

According to a massive genome analysis last year, supporting Cavalier-Smith's neomura theory, archaebacteria are sisters with eukaryotes. In the neomura theory they developed from actinobacteria as recent as ~ 850 Ma, which corresponds with fossil data. (Steroles which still in some cases are taken as evidence of ~ 2 Ga eukaryotes are also produced by actinobacteria.)

Extremophiles (and so the methanogens) of Earth are then late developments of evolution. While abiogenesis seems simple and robust enough, biospheres are likely a lot less easy to mature and get robust than extremophiles would indicate.

[Btw, and also less robust are then traces of methane as indicators of life, say on Mars. Albeit it could possibly been contingency that made it late here, it should be more researched.]

If we make it another 500 years I’d be surprised.

IIRC, average species lifetime is ~ 10^5 years, so we have plenty of time from now.

Actually, considering the recent publication of genome data showing that selection increased at least two orders of magnitude because of our population increase, we may already be "gone" compared to our ancestral species characteristics. It's the difference between biological (population isolation), fossil (bone variation) and anthropological (tool technique) species that makes us "still here".

As regards the biosphere this week (IIRC) there was this paper out on the sequestering effects from biologic and tectonic recycling vs stellar and radioactive heating drivers that could push the multicellular biosphere 2.5 Gy into the future by a thinning atmosphere. (And monocellular life even further – eventually the carbon dioxide running out will stop oxygenic photosynthesis and so oxygenic metabolisms, but not other pathways.)

Considering that multicellular life is but ~ 0.5 Ga, that leaves quite an impressive potential lifetime for our biosphere as we know it today. End even more for the primordial monocellular one, it may have 5-7 Gy or more total. Of course, 5 Gy into the future is pushing it even if that paper is correct.

Over the next billion years there will some other things which might make things tougher. The total land mass coverage of the Earth will go from 30% to maybe 40% or more as continents might continue to grow and ocean water is lost to tectonic subduction. This might change the Earth considerably, particularly if ocean coverage is split in two.

Probably a billion years from now life will begin to revert to a preCambrian type of existence as complex species become rarer. Two billion years from now Earth might come to resemble a cooler version of Venus. In 2 billion years or sooner the oceans will boil off and carbon containing dolomite rock will then be heated enough to drive off its locked up carbon into CO_2. Life might persist for some time as archaobacteria and extremophile species of prokaryotes.

Lawrence B. Crowell

All of this is connected to Poincare's demonstration that the stability of the solar system can't be demonstrated. In fact on a long enough a time frame it is inherently unstable.

Simple yes or no answer please: are the ideas of the nameless group of people (that you indirectly refer to) falsifiable?

The Earth could have been 3.7 billion years ago at 8.5AU from the sun.

I hope that you have employed a good proofreader for your book; I think that figure should be 0.85AU, not "8.5AU".

This nudging of the Earth outward almost exactly compensates for the increased heating of the sun in its evolution as a G-class main sequence star. This should continue for 1 to 2 billion years into the future. The Earth may be at around 1.05AU by then, which about compensates for solar heating up. Beyond that time the sun will heat up too fast for this gravitational 3-body mechanism to compensate. Yet this might extend the tenure for complex life on Earth from 500 million years to about a billion.

This has lead me so suspect there is some fine tuning in the structure of stellar systems. The motion of the Earth outwards is chaotic, with an average drift. If the Lyapunov exponent is much larger then the drift is outweighted by chaotic dynamics and the orbit not sustainable over the billion year time frames required for the evolution of life, or complex life. I did some analysis involving data on extrasolar systems known up to 2005, updated in the book, and only one other candidate came at all close to supporting a putative 1AU terrestrial planet in a stable manner. In all the other cases the putative 1AU planet would be either ejected from the system, crash into the Jovian or be forced into the star itself. Some statistics lead me to the ~ 1000 bio-planets per galaxy estimate.

We live in a unique and maybe highly exceptional place. Too bad we are treating it so badly.

Lawrence B. Crowell

I totally messed up my mental math there. I don't use it too often. I was thinking of 1 m versus 93 million MILES! and thinking over a million years those 1 meters will add up quite a bit. Apparently it's still small phew!

Making sure the Sun hasn't died by then is a different story, but even there I'm cautiously optimistic.

Oh dear. How annoying! };-D

That sounds rather significant?

Are you kidding me?
One meter (=10^0m) compared to 1,5*10^11m – if you call this significant then I don't know what could be insignificant to you!

Will you cry, when I tell you that the moon's orbit increases by 4cm a year?

Is the orbit being increased by 1 meter a year? That sounds rather significant?

In 5 billion years Earth will most likely look similar to Venus. The heating of the sun will have turned this planet into a hothouse, or a cooler version of Venus. Life on Earth will have ceased to exist 3 billion years prior to this terminal phase of the solar system.

Humanity will of course long since ceased to exist. If we can make it a couple of centuries into the future we might be doing well. The only thing I hold out for is that we can understand the foundations of the universe before we implode with the ongoing mass-extinction we are engineering. I just hope we hold on for that long. Life will be ticking away fine 25 million years from now. It will be very different from todays array of species and ecosystems — and highly unlikely H. sapiens or any continuation of our species will exist.

Lawrence B. Crowell

A black hole passing through the solar system?

"There is a small group of folks who shall remain nameless that suggested this had happened in the past."

Why do you need to be so secretive? Who are these people and what did they say? Did they suggest a new dynamic, as you put it?

But is there any dynamic that would speed up the process?

There is a small group of folks who shall remain nameless that suggested this had happened in the past.

This suggestion is possibly one of the reasons why electromagnetism has such a "bad rap" in astronomical circles.

I'm betting Hollywood will throw together a film about a planetary impact, likely directed by Michael Bay.

Hopefully Humanity will be out there somewhere colonizing other solar systems 5 billion years from now.

Unless we have already destroyed ourselves by then.

Cheers,
Yan