[chiralSPO (OP)]

I'm not sure where to put this (and I wouldn't be offended if this thread were moved to New Theories). I recently watched an excellent youtube video about Saturn's moon, Titan:

I realized that we would be “lava aliens” on Titan—where cryo-volcanoes release liquid water (with dissolved species, like salts and ammonia), which freezes back into ice at the surface, creating domes and other geological features almost completely analogous to our own volcano-dominated landscapes. Our body temp would certainly be high enough to boil their lakes (liquid methane and ethane) and melt some of their "rocks" (many of which are composed of water ice or heavy hydrocarbons, like benzene). We would need to bundle up to keep ourselves from freezing to death.

Likewise, we could imagine molten silicate-based life forms, from much hotter places (maybe even inside the earth???) which would need to bundle up quite warm to keep from freezing to death on our surface. They would instantly boil water, and could melt our rocks. Would they consume lava from volcanoes as we would water from cryo-volcanoes on Titan?

Many have previously discussed the possibility of silicon-based life, some recognizing that higher temps might be involved.

I wonder what sort of chemistry would be involved in such life forms...

[Tomassci]

From what I know about life, your lava forms would certainly have a bad time.

First, carbon is better forming various structures. You can't expect silicon doing DNA or similiar macromolecules.

Now, if silicon wasn't a problem, how would your life create heat? And how would it do structures? I can only imagine methane-based reactions.

[chiralSPO (OP)]

Certainly the chemistry involved would need to be incredibly different from anything we currently understand as life.

But I think that none of the requirements you bring up would be impossible, or even that far from reasonable.

Structure/macromolecules:
There are incredibly diverse ranges of silicate-based structures, each based on different arrangements of SiO₄ tetrahedra. ( see here for more info: http://butane.chem.uiuc.edu/pshapley/Environmental/L27/1.html )

silicate.gif (36.92 kB . 532x698 - viewed 1544 times)

And many of these structures are stable in the molten state. ( https://www.jstor.org/stable/99416?seq=8#metadata_info_tab_contents )

Metabolism/heat:
It is important to remember that it doesn't necessarily (and probably wouldn't) generate enough heat to keep itself molten in an environment like ours. Just as we cannot metabolize fast enough to maintain our 37 °C in an atmosphere at –180 °C. At the temperatures needed to keep silicates liquid (say 1500–2000 °C), there are still plenty of reactions that could reasonably create heat, or even be pushed uphill (like photosynthesis). (And who knows what pressures would be involved...)

[evan_au]

There are good reasons why silicate-based life keeps popping up in science fiction - because it is a plausible speculation (as speculations go).
- Most exobiologists continue to look for liquid water and carbon-based life, as we know that life can use these components
- But life using liquid ethane and methane as a solvent is another plausible speculation
- Another speculation I saw in science fiction was life based on diamond. Diamond is stable about 100-150km beneath our feet. At these temperatures and pressures, diamond could work like a semiconductor - the large number of black diamonds have high levels of elements that could turn diamond into a semiconductor.

I think it likely that there are forms of life in the universe that we would not even recognise as being alive.
- Our scientific equipment won't work for very long under many of these conditions  (and we ourselves will survive for an even shorter time)
- So for now, most scientists are focusing on forms of life based on water that we have a chance of recognising: "Life as we know it"...

[Kryptid]

A section of the textbook Life in the Universe: Expectations and Constraints by Dirk Schulz-Makuch and Louis N. Irwin does go into this subject matter. Here's a quote from chapter 6:

Feinberg and Shapiro (1980) suggested that the existence of lavobes, organisms that could exist in lava flows, and magmobes, organisms that could exploit thermal gradients or chemical energy sources within the molten rock. These organisms could make use of the chemical complexity of silicate rocks in which aluminum could replace silicon in the tetrahedrons and cation exchange reactions could occur in interlayer sites between the tetrahedral and octahedral sheets. For this to occur, silicates would have to be in the form of sheets, such as the clay minerals smectite and montmorillonite. Information could be represented as irregularities in the crystal lattice of minerals. A particularly intriguing example is the clay mineral amesite, which has a helical structure. Information could be encoded by substitution of silicon with aluminum.

It goes on later to say:

However, given the environmental conditions of Earth's crust and its composition (46% oxygen, 28% silicon) with abundant silicate melts, Earth should be more favorable than most other planets and moons in our Solar System for such a form of life. Yet no fossilized remnants or structures consistent with such an organism have been found, even though outcrops of igneous and volcanic rocks are abundant. Thus, the existence of such organisms seems very unlikely.