The Hadean is the earliest segment of geological time. In the conventional timescale it begins around 4.6 billion years (Ga) ago, the date of the oldest meteorites, and ends around 3.9 billion years ago – the age of the Earth’s oldest rocks. By contrast, the Moon’s oldest rocks date to around 4.4 Ga, implying that something occurred towards the end of the Hadean to wipe out Earth’s earlier geological history.

We can get some idea as to what that might have been by looking at our nearest neighbour. The highlands of the Moon are entirely disfigured by impact craters – the work of asteroids, not volcanoes. Over 70 craters have diameters ranging from 300 to 1,700 km. The very biggest, similar in extent to western Europe, measures more than 2,500 km across.

Conventional cosmology pictures the solar system as forming from a nebula of dust and gas, in a process where some of the aggregating bodies reached planet size and others did not. Embryonic planets increased in mass as smaller bodies collided with them, while bodies failing to reach planet size ended up as asteroids. Impacts from these bodies intensified around the end of the Hadean in an episode called the ‘lunar cataclysm’ or ‘late heavy bombardment’ – late because, for some reason, it did not occur until more than 500 million years after the period of planet formation. To what degree there were impacts before 4.0 Ga is unknown – a few impact melts and breccias date to around 4.2 Ga. Most date to around 3.9 Ga, the time of heavy bombardment, after which large impacts abruptly stopped.

Earth’s experience must have been no less traumatic than the Moon’s. It is estimated that more than 20,000 asteroids struck the planet. The reason we cannot trace impact craters on Earth is because its crust was destroyed and, in time, totally replaced.

While the severity of the event is clear, what caused the bombardment is not; it requires a lot of detective work. Most of the solar system’s asteroids are concentrated in a belt between Mars and Jupiter, and meteorite analysis indicates that they consist of minerals typical of rocky planets – predominantly iron, as occurs in the core of a differentiated planet, and silicates, as occurs in the crust and mantle. Many meteorites contain droplets that condensed from rock flash-heated to temperatures of 1800° C and vaporised. They appear to be debris from a planetary explosion rather than a proto-planetary nebula.

If we discount the radioisotope timescale, which tends to elongate even brief events over millions of years, such evidence (further discussed here) rather strongly suggests that there once existed more than the current eight planets, and at least one of them exploded, either in a collision (as cosmologists have been postulating) or as a result of thermonuclear heating within the mantle. Some of the material was vaporised and then re-compacted to form droplet-bearing asteroids; other material scattered through the solar system like so much shrapnel. Today’s asteroids, comets and rocky moons preserve what was left after most of the debris careered into the Sun if not other planets.

Earth’s former landmass having been annihilated, there is no telling whether it was inhabited. Since the fossil record traces a progressive recovery from the cataclysm, the implication is that it was. Life cannot just conjure itself into being. The sequence of fossils, the complexity of organisms, and the instability which gave rise to successive igneous and sedimentary deposits all support the conclusion that the cataclysm at the end of the Hadean represents the key to understanding Earth’s troubled geological history.

Reviving a lost tradition

The terms ‘cataclysm’, describing the end-Hadean bombardment, and ‘Noachian’, describing the earliest period in Mars’s preserved history, were chosen by scientists without any idea that they might refer to the same event as Genesis describes using such terms. Yet the possibility that science and historical tradition are converging upon one and the same event is now what is suggesting itself.

Genesis is not the only tradition that purports to remember such a crisis near the beginning of history. Similar traditions have been documented from pre-literate tribes throughout the world. Most refer simply to a global flood, but one or two give a hint that considerably more was involved. For example, take this excerpt from Mesopotamia’s Erra and Ishum, from the 9th century BC:

The very heavens I made to tremble, the positions of the stars of heaven changed, and I did not return them to their places.
Even Erkalla [the Underworld] quaked. …
The control of heaven was undone, the springs diminished, the flood-water receded. I went back, and looked and looked; it was very grievous.

(‘Stars’ were any celestial points of light, including planets.)

Genesis characterises the event as an undoing of the creation. Nowhere does it use the term ‘flood’. Like the Mesopotamian texts, it chooses a word reserved exclusively for what happened in Noah’s day: in Hebrew, mabbul, in Greek, kataclusmos. The word was unique because the event was. In contrast to an inundation which submerged and then uncovered the same surface, this was an upheaval in which water surged up from beneath the land and the land itself was shattered. Flooding was merely the consequence of that upheaval.

On that day all the springs of the great deep burst forth, and the windows of the heavens were opened, and rain fell upon the earth 40 days and 40 nights.

The ‘deep’ had been a great body of subterranean water which kept the land moist by oozing up through springs. (For details see The Cataclysm – more than a flood.) In the course of the cataclysm the primeval land was destroyed and the creatures that lived on it were ‘blotted out’ – a fate precluding even fossilisation.

What the opening of ‘the windows of the heavens’ refers to we are not told, but we can get some clues from the occurrence of the same phrase in the book of Isaiah. In a vision of a future day of wrath the prophet saw the heavens trembling, the earth being broken and rocked to its foundations, the host of heaven falling like leaves from a fig tree. The Apocalypse is even more explicit, visualising asteroids falling to the earth like figs shaken from their branches in a gale. People hid in caves and among mountain rocks, terrified of the wrath of their Maker.

There was just one time in Earth history when the planet experienced a cataclysm of this ferocity. That was at the end of the Hadean, at the very point where Earth’s geological record disappears. Likewise, the beginning of the following period, the Archaean, was the only time when the planet was wholly under water.

No Hadean rocks exist on the Earth because the eruption of the deep, coupled with the onslaught from outer space, shattered its crust and consumed it. Plants, animals and men were not fossilised because the land under their feet suddenly foundered, collapsing into the same interior magma from which, in due time, new land was to emerge. The ‘Hadean’ (from the Greek word Hades) is well named, for it was then that the original world was buried and became a separate underworld beneath the land of the living.