I’m not about to lose sleep worrying about such a collision because it will come as a surprise if it happens. Hardly anyone is watching out for these rocks. Anyway, a lump big enough to wipe out most of life on Earth might only be kilometres across, too tiny to see against the background of space until it’s too late.

Catastrophes are becoming respectable again. Since the last century, much of the earth sciences have been underpinned by the uniformitarian view that geological and evolutionary processes are slow compared to human lifetimes. Great global cataclysms were the stuff of the religious fundamentalists, largely discredited by the revolutionary thoughts of James Hutton and Charles Darwin. The past few decades, though, have seen increasing evidence of incoming space debris causing big bangs at regular intervals through the Earth’s history, often bringing bad news for life and clearing niches for new species. This book concerns itself with one such collision and other events of even greater age and violence.

The first is the comet impact that may have helped the dinosaurs (and many other groups) on their way to extinction 60 million years ago. The supernova that seeded our corner of space with the heavy elements is of less immediate concern but more fundamental consequence; we’re made of those elements. Most fundamental still, of course, was the big bang itself.

There is little doubt now that a comet hit the Yucatan Peninsula around the time the dinosaurs died out. The size of the crater indicates an energy release equivalent to millions of nuclear bombs, and chapter three starts with an evocative, but irritatingly data-free description of how that impact would have played havoc with the atmosphere and oceans.

Palaeontologists still argue about the mass extinction at the end of the Cretaceous: was it gradual or sudden, caused or just enhanced by the comet impact? Most geologists are tired of the debate and prepared to accept that such a big impact could easily have made global ecosystems crash, but this book reminds us how recently the whole theory was considered a bit loony. The authors were acquainted with the leading protagonists and spin a good yarn about how theories ebbed and flowed as the evidence gradually accumulated.

Ultimately, their concern as astronomically inclined physicists is the prospect of more asteroids and comets causing similar problems. After all, it is only 87 years since a tiny comet exploded with the power of a 10-megaton bomb over Siberia. What if next time it happened over New York? These are the passages that are most fascinating to an Earth-obsessed reader like me and, since reading them, I’ve gained a bit of a reputation in the coffee room as a prophet of doom.

Space, not Earth, occupies the remainder of the narrative. And it is a narrative, describing the development of various cosmological theories through the 20th century. There are plenty of personalities, plenty of “picture this” passages reminiscent of a popular magazine from back when science was still amazing, best read by torchlight by a wide-eyed teenager under the covers. The authors certainly convey this enthusiasm for the Universe and its mysteries: “There’s a load of really neat stuff out there and isn’t it fun to figure out how it all works?” Well yes, but this book is frankly a collection of neat stuff with a pretty tenuous thread linking the Earthlings with deep space. It is popular science, but anyone informed enough will quibble over the lack of bibliography.

The three big bangs in question are fascinating in their own right but form an odd combination in one book, so I’m not sure where the readership will come from. I hope the modern equivalents of wide-eyed teenagers pick it up. There really is a lot of neat stuff out there, and most of it is in here somewhere.

How old is our planet? The answer, ‘four and one-half billion years’,
is in the first sentence in Brent Dalrymple’s story of how scientists have
deduced the age of the Earth. The events that led Dalrymple to write the
book are rooted in the creationist, pseudoscience controversies of the American
law courts, and this in itself makes an interesting tale.

Dalrymple is an accomplished geochronologist who was retained as a witness
by the State of California in 1980, defending against a civil suit brought
by creationists who objected to the teaching of evolution as fact in public
schools. The state had assembled a formidable panel of scientific expertise,
and although ultimately never called upon, Dalrymple acquired a reputation
as a scientist who was willing and able to debate the creationist issue
in legal proceedings, informal seminars and the press.

Be aware, though, that this book is not a philosophical or theological
debate; it is a well-informed scientific textbook based on the author’s
painstaking background research in a number of fields.

By starting with ‘The Answer’, Dalrymple sets out his stall. This was
a wise move; it would take an extraordinary writer to maintain the suspense
of a whodunnit through the development of theories and techniques pertaining
to a single question in earth sciences, however fundamental. The answer
has been hard-won down the centuries, however, and a wide variety of disciplines
have been brought to bear upon the question.

Early attempts to deduce or estimate the age of the Earth form the first
main section of the book, and provide some of the most entertaining reading.
James Ussher’s celebrated biblical chronology of 1650, which placed Creation
in the evening of 22 October 4004 BC, was by no means the earliest recorded
‘Answer’. About 2000 years before Ussher, the Hindu priesthood decided that
creation had occurred 2 billion years ago. The accuracy of this guess was
unsurpassed until the 20th century.

Biblical chronologies are all good fun, but the real entertainment
from a modern perspective comes with the work of 19th-century scientists,
such as Lord Kelvin, whose estimates were based on observational data and
sound physical principles. Physicists calculated the cooling rate of the
Earth and the effects of orbital forces, while geologists, who trusted their
own observations rather than the mathematical juggling of the establishment,
appealed to erosion and sedimentation rates.

They were all spectacularly wrong because they had misunderstood processes,
guessed starting conditions and overstated the certainty of their assumptions.
In some cases, they were soundly criticised on these grounds by their contemporaries.
Ironically, much modern scientific debate revolves around the same criticisms.
Perhaps we should take a lesson from the authors who claimed their work
to be no more than ‘wild speculation’, yet whose answer is often all that
remains in the popular perception about the age of the Earth.

Ultimately, the age of the Earth and everything in it can only be addressed
by radiometric dating. As a background to the main substance of the story,
modern radiometric methods are explained in a chapter that is as clear and
concise as any I have read. Here the book stops being journalism and gets
its teeth into the subject; lead isotope systematics are tortuous enough
for those of us who deal with them daily, and Dalrymple has probably made
this process as accessible as possible. Although all the principal dating
methods are described, we find out that the whole story hinges on the decay
of uranium to lead. A chapter relates the oldest rocks found on the Earth,
and here the diversity of techniques available to the modern geochronologist
becomes invaluable, giving us a minimum age constraint that is bolstered
by data from lunar samples.

Another chapter introduces the meteorites, the oldest and most primitive
rocks available to scientists, which are crucial to the story because the
‘age’ of the Earth really means the time at which the matter of the Solar
System first segregated into discrete bodies. The chapter devoted to lead
isotopes just about wraps things up, but there follows a brief account of
astrophysical methods by which the age of the Universe has been estimated,
as well as a concluding chapter with the tantalising title of ‘What we
know and do not know’.

Although the author has an easy conversational style that allows us
to skip the mathematics if we wish, this book is by no means light bedtime
reading. A tremendous amount of information is presented or cited between
the covers, and as such it makes a useful source book. A comprehensive
glossary is included to help the nonspecialist escape the jargon trap. We
all know ‘The Answer’, but if you want to know how the question was asked,
this book will certainly tell you.

Simon Inger lectures in earth sciences at the University of Leeds.