meanwhile, in order to simulate the early earth…

Ian said that “island arcs” are what we’re most interested in. But that’s the issue here – island arcs, by nature, are difficult to generate through some non-arbitrary process. You can manually create them, but then how do you know if the results are generalizable to other sets of island arcs? That’s why it’s important to have a generative process that’s actually random.

So… I need to learn a bit more about this.

Now, from preliminary “research”, I get this:

An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates.

So – how do they relate to the early Earth?

Well – we go here: http://en.wikipedia.org/wiki/Geological_history_of_Earth

In contrast to the Proterozoic, Archean rocks are often heavily metamorphized deep-water sediments, such as graywackes,mudstones, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks. The high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent deep-sea sediments eroded from the neighboring island arcs and deposited in a forearc basin. In short, greenstone belts represent sutured protocontinents.^[9]

Anyways – we probably don’t need to be concerned with the low-grade metamorphic rocks, which are only found in the deep sea.

Also http://thisoldearth.net/Geology_Online-1_Subchapters.cfm?Chapter=8&Row=2

Although the Archean crust is made up of many different types of rocks the most abundant rocks occur in greenstone belts and granite-gneiss complexes. Granite-gneiss complexes are actually composed of a variety of rocks, with granitic gneiss and granitie plutonic rocks being the most common. These rock associations were probably the result of igneous activity within and around volcanic island arcs. Although they are much less abundant then granite-gneiss complexes, greenstone belts are incredibly important to unraveling some Archean tectonic events.

The typical greenstone belt has three main components; the lowest unit consists of ultramaffic volcanics such as basalt and peridotite, the middle unit is also volcanic but maffic in nature consisting mainly of basalt; the upper units are mostly sedimentary and consist of greywackes, shale and quartzites.

So… first of all, we have ultramafic rocks of high density. Here – it is important for us to consider the albedo of our rocks, and then to input this albedo into our CAM models. There’s actually an easy way to get the albedo of any rock across both the visible *and* IR spectrums – we try to find some online spectral libraries

· ASTER spectral library – http://speclib.jpl.nasa.gov/

· USGS spectral library – http://speclab.cr.usgs.gov/spectral.lib04/spectral-lib04.html

So from that, we can try to figure out the spectra.

Now – back to the main issue – we need land distributions. One thing is this: it’s quite possible that there was no continent formation

The Earth of the early Archean (3,800-2,500 Ma) may have had a different tectonic style. During this time, the Earth’s crust cooled enough that rocks and continental plates began to form. Some scientists think because the Earth was hotter, that plate tectonic activity was more vigorous than it is today, resulting in a much greater rate of recycling of crustal material. This may have prevented cratonisation and continent formation until themantle cooled and convection slowed down. Others argue that the subcontinental lithospheric mantle is too buoyant to subduct and that the lack of Archean rocks is a function of erosionand subsequent tectonic events.

In this case, what can we do for our random generation? One question: how did the number of volcanic hot spots change with respect to time? (one key question: how many volcanic hot spots does Io have? Io is extremely volcanically active, and almost all of its volcanic activity comes from hot spots, as it is too small to support plate tectonics). We don’t have any definite idea – I discussed this issue with someone doing this research at CASS2011. There’s also a paper on this I’ll try to look up later.

So… What should we then do? Well, how were the island arcs formed? Plate tectonics was MUCH more active than it is today – so could it have been significant enough to form island arcs on the boundaries of subduction zones? Hmm – this is an issue I’ll have to spend some more time thinking about. I also have a few other issues to address regarding the gas constants (David Catling actually just sent me a very nice email after reading the constants file I looked at)