For many centuries, the search for concordances with ancient texts dominated the timeline of natural history, and there was no connection with geology. This scenario did not appeal to Robert Hooke (1635–1703) who, in 1662 at the age of 27, was appointed the curator of experiments at the Royal Society. He became a great polymath, Renaissance man and indeed a jack of all trades: architecture, astronomy, biology, mechanics, optics and geology came within his remit. His numerous inventions included the iris diaphragm, the universal joint and the compound microscope. He accumulated a huge personal fortune (£8000 in gold and cash, equivalent to a few million pounds today) when he and his friend Christopher Wren worked intensively in 1666–1680 as the principal architects rebuilding London after the Great Fire. Hooke’s career as curator at the Royal Society established his reputation as the first natural philosopher to focus on experiments made with precision instruments. For him, Nature was a great machine or engine in motion, the secrets of which could be uncovered with ingenious devices.

This chapter completes the story of the acceptance of plate tectonics, which marks the beginning of the modern period of Earth system science. This final approval required additional contributions by several researchers, with the key papers being published in 1968. Jason Morgan’s work on crustal blocks, of which he had given an impromptu preview at the American Geophysical Union in April 1967, proposed that on Earth’s dynamic surface 20 crustal blocks move relative to each other, endlessly jostling for their place in the jigsaw. Simultaneously, Xavier Le Pichon, a young French geophysicist who worked with the Ewing brothers at Lamont Geological Observatory from 1963 to 1989, connected the kinematic ideas of Morgan, McKenzie and Parker to the vast data sets held at Lamont, particularly the magnetic profiles. Le Pichon’s computer model demonstrated that the motion of six large rigid blocks completed a jigsaw that covered most of Earth and could accurately account for the evolution of ocean basins. His model of June 1968 indicated that plates do indeed form an integrated system in which the sum of all crust generated along 50,000 kilometres of ocean ridges equals the cumulative amount destroyed in the subduction zones.1

The outstanding issue with reversals concerned the fidelity of the spreading ocean crust as a magnetic tape recorder: some geologists asked themselves if the reversals could have occurred spontaneously in the rocks sampled. This conundrum could be resolved by obtaining accurate dates of formation for groups of rocks with normal and reversed polarity, and so determining whether the rock magnetism reversed in sync or not. In the 1950s, uranium–lead (U–Pb) radiometric dating was not accurate enough for younger rocks because the half-life of uranium is so long, which meant the quantity of lead was insufficient for analysis by the technology then available. By the end of the 1950s, two groups of geochemists, one at the United States Geological Survey (USGS), Menlo Park, California, and the other at Australian National University, had developed the techniques of potassium–argon (K–Ar) dating to the stage where it could be used on young rocks, such as lava flows, with ages of hundreds of thousands to a few million years.

In this chapter, I assess the connections between the studies of deep carbon as the carbonate component of fossils and the role of deep time for a reconstruction of Earth history. I leave the history of the absolute calibration of deep time for the following chapter. William Smith’s standout contribution to the practice of geology in England was his achievement in tracing the courses of the strata. He introduced the principle of faunal succession in his book Strata – Identified by Organized Fossils, a short book with colored plates published in 1816. That publication turned his private cabinet of curiosities into a public resource of the characteristic fossils in rock formations.

A fundamental goal of geophysics is the construction of a comprehensive understanding of the structure and dynamics of Earth’s interior, which is inaccessible to direct measurement. Therefore, indirect methods such as the interrogation of seismic data obtained at the surface are used to model the physical properties of the interior. Interpretation of data requires the researcher to solve an inverse problem. In scientific inquiry, the solution of an inverse problem requires interpretting data to discover underlying causes. When we ask, “Why is it raining today?” we are posing an inverse problem: we have the data (getting wet!) and want to know the cause (frontal system, thunderstorm, etc.). The reverse situation – posing a forward problem – is to ask, “Will it rain tomorrow?” This can be tackled by computing a forecast from an atmospheric model. This chapter outlines an important case history in which the mere acquisition of data for its own sake led to a fascinating inverse problem: Why is the longest and greatest mountain range on Earth in the middle of the oceans?

Carbon is the fourth most abundant element in the universe. It is outweighed by hydrogen, responsible for nine-tenths of the mass of ordinary matter in the cosmos, and by helium. Hydrogen and helium are remnants of the Big Bang: they are products of the first three minutes of our fireworks universe. Oxygen, the third most abundant element, and carbon are ashes from the explosive finale of the evolution of stars.

When the formation of the Moon and the phase of giant impacts had mostly run its course, a final round-up of the remaining planetesimals took place. Gravitational forces exerted by the eight planets scoured interplanetary space: some planetesimals were flipped into the Sun, others thumped into terrestrial or giant planets, and the remainder were expelled to interstellar space by gravitational slingshot effects. Unsurprisingly, gravity’s purge of the solar system was not an entirely clean sweep. Comets, asteroids, meteors (meteorites once they make the journey through Earth’s atmosphere) and mere specks of dust lingered. In our age, this debris has become an indispensable archival source of data for revealing how, over billions of years, the elements have been sieved and sorted for distribution throughout the solar system. Detailed investigations of the composition of asteroids and meteorites became a hot area of planetary science research at the beginning of the present century. In 2015, the NASA spacecraft Dawn began a three-year survey mission to Ceres, the largest asteroid.

The currently accepted age of Earth is 4.55 billion years, a figure that has not changed significantly for 70 years. From the 1850s to the 1950s, the question of the age of Earth advanced from simply being an airy speculation driven by those geologists willing to allow an indefinitely large amount of past time and those biologists who favored evolution. Unexpected discoveries in physics and chemistry transformed Earth history from intelligent guesswork to a precision science defined by physical laws. This chapter summarizes a century-long pathway of discoveries in physics that would dramatically improve our understanding of the age and properties of the deep Earth, and in particular the deep secrets hidden locked in the carbon atoms in the interior of Earth.

Carbon is the fourth most abundant element in the universe, and it is one of the most important elements on our planet. In this chapter, we introduce the story of Earth’s carbon all the way from its synthesis in the first generation of stars in our universe, to its incorporation in the solar nebula, where the Sun and planets formed nearly five billion years ago. Carbon’s journey from deep space to deep Earth took almost nine billion years. It is the basis of all life on Earth, where it serves as the structural backbone of molecules large enough to carry biological information. One of carbon’s most important features is that it readily forms chemical bonds with many other atoms. This property is the driver behind the biochemical reactions needed for metabolism and propagation. The history of life on Earth is therefore inextricably linked with the history of these elements.

Diamonds form deep in the mantle, where they mostly remain unless propelled to the surface in a volcanic eruption. Diamond is by far our most important mineral messenger for discovering the history and chemistry of Earth’s convecting mantle. Diamond provides a window to otherwise inaccessible geological processes that churned away 100 kilometres underground and often occurred billions of years ago.1 Chemically, diamond is exceptionally pure: 99.9 percent or more elemental carbon. Diamond lasts almost forever, being the hardest known natural material by quite a margin. And since 1948, De Beers has used the marketing tagline “A diamond is forever” continuously to promote its diamond engagement rings.

Earth is the only known habitable planet in the solar system. Although there are half a dozen planetary moons that may have habitable zones beneath their surfaces, astronomers have yet to find an exoplanet with conditions deemed suitable for life on its surface. From a geological point of view, Earth’s distinctive features include the presence of life, the abundance of liquid water, the long-term tectonic system and the profusion of organic carbon in contact with the oxygen-bearing atmosphere. The carbon cycle inextricably binds biological life at the surface with carbon on the move in the interior. Through laboratory experiments, we have discovered that, following subduction, carbon-bearing materials undergo great transformation in the high-pressure hothouse of the mantle. Earth’s subduction factory plays a key role in the deep carbon cycle by feeding the mantle with different carbon phases, four-fifths of which are carbonates and one-fifth organic carbon, proportions that have remained relatively stable since Earth’s biosphere became established.

My engagement with the new field of deep carbon science began in September 2015, when Marie Edmonds of the Department of Earth Sciences at the University of Cambridge asked if I would be interested in researching a history of deep carbon science. By then I had been working in the history of science for some 15 years, following early retirement from Cambridge University Press. Much of my academic activity had been limited to the history of astronomy and cosmology in the twentieth century. In the geosciences, my knowledge of its pioneers was more or less limited to what had been achieved by people in Cambridge, particularly in tectonics, which was centre stage when I commenced my doctoral research at the Cavendish Laboratory in the radio astronomy group that had discovered pulsars. Over a working lunch at Queen’s College, Marie told me about the exciting multidisciplinary mission of the Deep Carbon Observatory (DCO). I was immediately attracted by the vast transformative scope of this large-scale research programme with its focus on four clearly defined themes to be undertaken by four scientific communities working collegially. Through this framework the DCO had already completed six years of comprehensive exploration of deep carbon in Earth’s crust, mantle and core. By this point in our conversation I was beginning to wonder how on Earth I could have anything to offer, given that my limited experience as a historian of science had been all about the pioneers who looked up in wonder at the mechanism of the heavens. So I was delighted to receive an invitation to participate as a historian of science at a DCO planning meeting soon to be held in a rural retreat at the University of Rhode Island in late 2015.

This chapter on deep carbon subsurface life opens at the 2018 Fall Meeting of the American Geophysical Union (AGU) in Washington, DC, where Deep Carbon Observatory (DCO) scientists showcased stupendous discoveries about deep life.1 Earth’s most pristine ecosystem, the deep biosphere, is home to members of all three domains of life: Archaea, Bacteria and Eukarya.2,3 Archaea and Bacteria are microbes, and the Eukarya include fungi, algae, unicellar organisms with organelles, as well as plants and animals. Unicellular organisms exist everywhere on Earth’s surface, from the thermophiles in the hot springs of Yellowstone National Park to the microbes living in your refrigerator or below the ice sheets of Siberia and Antarctica. The huge surprise that captivated the public following the press releases at AGU was the immense mass of carbon directly associated with subsurface bacterial life. Researchers estimated that this reservoir holds 15–23 billion tonnes of organic deep carbon.

At the beginning of the twentieth century, conventional geological authority reposed peacefully on the bedrock of uniformitarianism. The received wisdom held that geological processes had changed little across time and that there was no evidence of sudden large-scale changes. Furthermore, the geology of the ocean floor was not considered to be an area of fruitful inquiry. The geological continuity of strata and mountains across deep oceans was explained by the cooling and contracting Earth. Most of the European geologists had accepted the framework of the evolution of Earth’s rocky crust that Europe’s leading geologist, Eduard Suess (1831–1914), had developed from the mid-1880s.