The Hadean is the earliest segment of geological time. In the conventional timescale it begins around 4.6 billion years (Ga) ago, the age 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. The surface of the Moon tells us what that something was, for the entire Moon is disfigured by impact craters – the work of asteroids. Over 70 craters have diameters ranging from 300 to 1200 km. The very biggest, similar in extent to western Europe, measures 2500 km across.
Atheistic cosmology pictures the solar system forming from a nebula of dust and gas. In the process of aggregation, some bodies reached planet size, 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 a puzzling 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 – several impact melts and breccias date to around 4.2 Ga, so there may have been some. While the majority date around 3.9 Ga, there is a strong possibility that they are dominated by ejecta from the biggest and one of the last basin-forming impacts on the nearside, that which produced the Imbrium crater. After 3.8 Ga large impacts abruptly stopped.
Sooner or later, Earth’s experience must have been no less traumatic. The number of asteroids striking the planet is estimated to have been in the thousands. The only reason we cannot trace impact craters on Earth is because its crust was destroyed and, in time, totally replaced.
While the severity of the bombardment is clear, the cause is not. Most of the solar system’s asteroids lie concentrated in a belt between Mars and Jupiter. Meteorites indicate that they consist of minerals typical of rocky planets – predominantly iron, as in the core of a planet, and silicates, as in the enveloping crust and mantle. Many meteorites contain droplets that condensed from rock flash-heated to temperatures of 1800° C and vaporised. They are more easily interpreted as debris from a planetary explosion than as leftovers from a proto-planetary nebula.
If we discount the radioisotope timescale, which elongates even brief events over millions of years, the meteorite evidence (further discussed here) 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 core and 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 had careered into the Sun and other planets.
There is no telling whether Earth’s former landmass was inhabited. In appearing to trace a progressive recovery from the cataclysm, the fossil record implies that it was. Life cannot just conjure itself into being. Taken together, the sequence of fossils, the complexity of fossilised organisms and the instability which gave rise to successive igneous and sedimentary deposits support the conclusion that the cataclysm at the end of the Hadean represents the key to understanding Earth’s troubled history.
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. Perhaps providentially, in these last decades science and historical tradition have been converging upon one and the same event.
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 [Hades, the Underworld] quaked.
The control of heaven was undone, the springs diminished, the flood-water receded. I went back, and looked; it was very grievous.
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.
There was just one time in history when Earth experienced a cataclysm of this ferocity. That was at the end of the Hadean, at the very point where its geological record disappears. The beginning of the following period, the Archaean, was the only time when Earth was wholly under water. Fossils thereafter trace the process of ecological recovery.
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. As the land foundered under their feet, plants, animals and men were obliterated. Eventually the land itself was subducted into the mantle. Like the words ‘cataclysm’ and ‘Noachian’, the term ‘Hadean’ (from the Greek Hades) is well chosen. The original world became a separate underworld beneath the land of the living.