The Archaean is the oldest time division in Earth’s extant crustal record. Radioisotope dating gives it an age of 3.9-2.5 billion years, spanning 1.4 billion years, or just over a third of the total length of Earth history. The only remains older than 3.9 billion years are isolated crystals of the extremely durable mineral zircon (ZrSiO₄), which have ages of up to 4.4 billion years. In recolonisation theory the Archaean equates to the first few decades immediately after the Cataclysm, at the start of which the planet was under water and new land was forming in place of the old. How well does this idea match up with the evidence?

Water before there was land

The oldest rocks are predominantly igneous – they originated directly from magma rising from the Earth’s interior. As such they are evidence neither for nor against the existence of water. However, chemical sediments in Greenland dating to the early Archaean certainly precipitated from water, and submarine deposition is also indicated by widespread pillow basalts – igneous rocks that contracted into pillow shapes as they came into contact with water and were quenched. Indeed the rarity of clastic sediments – sediments normally formed by the breaking up of rock in the course of weathering, river action and tectonic upheavals – shows that dry land was rare. The general picture for the early Archaean is of a world that was almost entirely under water, with here and there small volcanic islands protruding like ancient versions of Surtsey Island and rapidly shedding material from their sides to leave sedimentary deposits around them.

This agrees well with the recolonisation idea. Early on in Earth history a cataclysm occurred, in the course of which, according to one tradition, ‘the waters prevailed so mightily upon the earth that all the [previously existing] high mountains under the whole heaven were covered.’ Contrary to what one would expect if the Earth had a solar nebula origin, the geological record shows that immediately after the cataclysm the world was dominated by oceans. There were no continents as such. With the old creation destroyed, terrestrial crust had to form anew, by massive underwater extrusions.

High ocean temperatures in the Archaean

In recolonisation theory ocean temperatures are expected to have been generally high, owing to the energy released by the impacts of asteroids, the heat absorbed from the granitoids and other igneous bodies that were erupting under water and the sheer intensity of the volcanism.

In the conventional scenario high temperatures are predicted only for the preceding Hadean, not for the Archaean. Massive amounts of heat are thought to have been released during the Hadean by:

• gravitational energy, as the Earth condensed from the primordial nebula that supposedly gave rise to the whole solar system
• the collision with some other planet-sized body that gave birth to the Moon
• bombardment by stray asteroids and meteoroids, interpreted to be products of accretion elsewhere in the solar system, and
• much higher heat production from radioactivity, since the ratio of parent to daughter elements was then much greater.

In such conditions it is difficult to postulate that oceans could have existed at all. Until recently, the absence of rocks older than Archaean was taken as evidence that the Earth was too hot even for solid crust to form.

But no longer. The discovery of minute Hadean zircons among conglomerates of late Archaean age has obliged a rethink. These crystals are so durable that they can persist even when their parent rock is destroyed, whether by remelting or erosion, and the high ratio of ¹⁸O to ¹⁶O in them shows that the magma from which they crystallised must have been in contact with water. Oceans did exist at this time – 400 million years earlier than geologists had thought possible.

The zircons show that the scenario whereby the Earth condensed out of particles of dust billions of years ago is seriously flawed. Recolonisation theory offers a simple explanation for the presence of zircons amongst the conglomerates. They are the remains of the first minerals to crystallise within the Earth’s interior before the cataclysm, at a time when mantle temperatures were rising, not falling. During the cataclysm itself conditions were so violent that all but the most durable minerals in the upper mantle were destroyed; only zircons survived, subsequently mixed in with new Archaean magma.

That may be why the cores of the zircons can be up to a billion years older than their rims: the cores reflect melt coming into contact with subterranean water before the cataclysm (hence localised cooling and crystallisation), whereas the rims reflect a second, post-cataclysm episode of melting and crystallisation as erupted magmas formed new crust in place of the old.

In the Archaean, conventional geology encounters the opposite problem from that in the Hadean. If there were already oceans, and the Sun (as standard cosmology requires) was then radiating 25-30% less heat than it does today, we should expect comparatively low, and over the course of 1.4 billion years steadily declining, ocean temperatures. However, oxygen and silicon isotope data indicate ocean temperatures persisted at high levels throughout the Archaean, declining only in the Palaeoproterozoic. Some therefore speculate that high volumes of methane existed in the atmosphere to act as a greenhouse gas and keep the planet warm.

Where massive thicknesses of igneous rock were being extruded, sea temperatures must have been high. Only heat-loving types of bacteria could have survived. Other marine organisms would have cooked, or suffocated for lack of oxygen, which becomes progressively less soluble as temperature rises. Elsewhere, marine organisms were able to struggle through. To some extent the erupted subterranean waters and the downpour of extraterrestrial waters would have mitigated the heat produced by the asteroid impacts. Since the asteroids approached from a direction mostly parallel to the plane of the ecliptic, the bombardment would have been least intense at latitudes close to the then poles, owing to (i) the greater thickness of the atmosphere at angles oblique to the Earth’s surface and (ii) the proportionally greater area exposed. In such regions the waters might have been considerably cooler and offered a refuge for marine life. It may also have been there that a solitary vessel, laden with terrestrial animals and a family of human beings, drifted on the seas in the hope that land would be found. They landed, eventually, on an Archaean surface.