While meteorites are the oldest datable objects in the solar system, they are not the remnants of a constructive process, but of a destructive process. There are no demonstrably pristine bodies drifting round the solar system, and meteorites cannot be used to measure its age. The age of the solar system, including the Earth, must be significantly greater than the meteorites. As Scott et al. (2007) are forced to admit, the ‘record of planetesimal and protoplanet accretion recorded in meteorites is not consistent with planetary accretion and disk evolution models’.
The relative and absolute ages of meteorites are determined by radioisotope dating, whereby the proportion of a radioactive element (normally 26Al) to its decay product (normally 26Mg) allows the investigator to calculate the time taken for one to decay into the other. The oldest such dates mark the point at which cooling of the matrix sealed the system, preventing the isotopes from being exchanged with its surroundings. Without such isolation, radioisotope dating would give a false result.
Isotopic closure does not therefore represent year zero. There was an unknown period of existence prior to that point. Chondrules, for example, were once part of a planet or large asteroid that had undergone high-temperature heating. In the course of heating up, the planet’s interior might have undergone a degree of differentiation, where heavy minerals and elements separated out and sank towards the centre, and prior to that there might have been a period when the planet was cooler. In the absence of older radioisotope dates there is no telling how long that period was. ‘Growing evidence exists that chondritic meteorites represent the products of a complex, multi-stage history of accretion, parent body modification, disruption and re-accretion’ (Sokol et al.).
In order to arrive at an absolute date, intervals based on short-lived radioisotopes have to be linked to a chronology based on long-lived isotopes. Short-lived isotopes can provide only a floating chronology, terminating with the extinction of the parent isotope, and that chronology will only be valid across the whole solar system if the distribution of the isotope through the solar system was initially homogeneous. Otherwise meteorites from different bodies will yield different ages even if their age is the same. The whole nebula hypothesis depends on the assumption of homogeneity. But it may not in fact be correct (Kunihiro et al., Brennecka et al. 2009). Chondrules show a span of ages as long as the longevity of 26Al itself, and can yield different ages even within the same meteorite. Iron-poor chondrules, for instance, tend to yield slightly older dates than iron-rich chondrules. Some CAIs show no evidence of live 26Al at all at the time of formation. On the other hand, one would not expect the assumption of homogeneity to hold good if the isotopes were synthesised in the interiors of planets of different sizes, vaporising at different times. At this point in time radioisotope dates, it appears, can reliably give only an approximate indication of relative chronology.
It is also doubtful whether radioisotope dating can provide an absolute chronology. Creation theory postulates that rates of radioactivity have exponentially decreased over time. No fragment has survived from the original world, because radioactivity and thermonuclear fusion melted the interiors of the terrestrial planets, blanketing their surfaces with magma. Earth was not exempted, although in its case the heat of the upwelling magma was mitigated by a large body of water beneath the former land. Mercury shed the greater part of its mantle (insofar as it had differentiated into core and mantle, differentiation may have continued after shedding). Planets larger than Earth and the original Mercury exploded entirely.
- CAI particles are thought to be the first condensates from a primeval nebula. But in that case, how is it that they failed to accrete with other accreting material in the protoplanetary disc for up to 3 million years? This is known as the “storage problem”.
- Because CAIs and chondrules have different compositions, they are thought to have formed in different parts of the solar nebula, CAIs close to the Sun, chondrules further out. It is not clear, however, how CAIs and chondrules could have remained in separate regions for up to 3 million years before coming together in the chondrite parent bodies.
- CAIs and chondrules were mostly just millimetres in size. Gas drag should therefore have caused them to spiral into the Sun within a few tens of thousands of years. The dating evidence that they lingered in the disc for 2-3 million years is inconsistent with the lifespan of small particles in the early solar system (Bizzarro et al. 2004, Rudraswami & Goswami 2007). Even more problematic is the inference that CAIs formed close to the Sun and then drifted in the opposite direction, beyond Mars.
- As we have seen, many investigators are agreed that chondrules originated in impacts: sudden, brief, catastrophic events. The main difficulty with this view is that chondrules sharing the same origin seem to have gone on forming for over a million years (e.g. Rudraswami et al. 2008).
- Differentiated meteorites come from parent bodies that were once molten. Radioisotope dating, however, often gives ages too late for the heat energy to have come from the decay of short-lived isotopes. These would have been largely exhausted and the heat from them would have radiated away (Baker et al. 2005). Indeed, even if the asteroids had accreted immediately after the synthesis of 26Al, the heat generated would would have been insufficient to melt them. The maximum temperature reached would have been around 940 K, far below both the 1260 K threshold at which iron starts to melt and the 1600 K threshold at which silicates begin to segregate (Kunihiro et al.).
- Collisions between protoplanets are thought to have been common in the early days of the solar system, around 4.56 billion years ago. This is the explanation for why Mercury, the Moon and Mars are so heavily cratered, with some craters measuring thousands of kilometres across. However, the ‘Late Heavy Bombardment’ that caused most of the craters dates to around 3.9 billion years ago. The standard chronology postulates an improbable lag of some 600 million years.
These problems and inconsistencies are strong evidence that rates of radioactivity were dramatically higher at the time, causing radioisotope dates to be correspondingly exaggerated.
The presence of short-lived radionuclides, calcium-aluminium-rich condensates and silicate-rich melt droplets in the oldest meteorites is no coincidence. Ad-hoc surmises about supernovas, about the solar system having originated from a dust-rich nebula, about condensates and melt droplets lingering in separate parts of the nebula for millions of years and then coming together fall short of the mark. Everything in the chondrites is of a piece. The asteroids, the comets and the moons tell the same story, one that goes back to a brief episode in history when the whole solar system was given over to destruction. Nothing is as it was when it was created.