Nature 2021 February

We are stardust!

In her song Woodstock, Joni Mitchell had the lines “We are stardust, billion-year-old carbon…”. In fact, it is nearer four billion-year-old carbon, which eventually became part of our solar system. But carbon is but one element of many, along with H2O, a vital molecule for life to evolve. Hydrogen is the oldest element, being formed not long after the Big Bang 13.8 billion years ago along with helium and lithium. Other heavier elements were formed in second-generation stars, including carbon and magnesium, two of those vital elements amongst many others for life to develop.

When stars ‘die’ there is an explosive discharge of elemental material distributed into space, including a kaleidoscope of elements and particles. In our case these expelled fragments of an old sun led to the formation of third and successive suns and planets. Still more elements were deposited when proto-planets collided with a fledgling earth. Much later, an extinction event 66 million years ago occurred when an asteroid from beyond the solar system caused a right-angled change in the direction of the evolutionary process. This was the last but most significant of these cataclysmic events and changed the direction of evolutionary history in our favour. Meteorites are thought to have deposited both rare earth metals and much of the oceans’ water.

At a cellular level our bodies comprise a vast assembly of both molecular atoms and individual elements. We are merely temporary custodians of these atoms which we share with other organisms: the flora, fauna, fungi, bacteria and also the landscape: the air, water, soil and rocks. On our passing we return these elements which we borrowed for three score years and hopefully a good few more.

Water is essential for all life. Whereas we take some water from the plants we eat, most of our water comes from just drinking clean water drawn from rivers and lakes but largely from under the ground. How that water gets there is too complex to explain here, save to realise water in the woodland landscape of the Chilterns is a precious commodity. Nearly all summer rain rapidly evaporates back into the atmosphere, either from the leaves in the tree canopy or from close to the ground surface.

Mosses and ferns that cope with the heavy shade of the beech woods capture vital amounts of fresh water and made fresh water available to post Ice Age human inhabitants in the Chilterns. Elsewhere it might drain off into ditches, eventually running into rivers or held by lakes. In these hills it is quickly lost from the surface, passing through the soil into porous chalk aquifers. This process also ensures all those vital minerals and trace elements that dissolve into the water as it passes through soil can be drawn up by the deep roots of trees. One other benefit of the wooded landscape and grassland of the Chilterns is that the soil is largely protected from erosion and the clays and chalks provide a rich source of trace elements which have contributed to the diverse mineral waters extracted for commercial purposes from the aquifer.

Plants and trees must draw most of the elements they need from the soil. The exceptions are the carbon the plant needs drawn into the leaves from the atmosphere as CO2. Similarly, oxygen and hydrogen are incorporated into the plant’s organic chemicals through the ‘splitting’ of water and carbon dioxide during photosynthesis. Without this process occurring in plants, animals could not have evolved, nor could humans have become a dominant species.

The climate of the Chilterns is still warm and moist enough to support woodlands, though it is increasingly threatened by climate change. Though rich in minerals and elements, beech and oak leaves are extremely hard to break down. Luckily, the woodland floor is rich in invertebrates (beetles, woodlice etc) that can start this process to recycle these elements. Earthworms drag leaf litter into the soil and in doing create underground channels helping water to drain to lower levels through the humus-rich topsoil. Furthermore, minerals are released into the water by fungi and bacteria working on and beneath the soil surface. Much of this rare reserve of elements is held by microorganisms in the soil and later absorbed by trees and reincorporated to provide the materials to create new growth of branches and leaves.

Although omnivorous, humans in the post Ice Age Chilterns needed access to the valuable nutrients tied up in the vast woodland trees and grassland plants. However, although fruit, seeds and roots were available, more energy-rich food was needed, which was in the parts of plants humans cannot digest. Unlocking access to these nutrients was accomplished through a complex food chain which had developed alongside the forestation of the Chilterns.

The oaks and beech woodlands were a source of food for leaf-eating caterpillars and other larvae and wood boring invertebrates like beetles. Invertebrates cannot breakdown the tough plant cell structures made of cellulose or lignin without relying on gut bacteria to do their bidding. Once released for use by invertebrates these elements can be used to create carbohydrates, fats and proteins. In turn small birds and mammals feasted on these insects building these energy-rich foods into their bodies. Unlike other predators, such as owls, raptors and wolves, humans could not readily access most of this valuable food resource. Consequently, the landscape would have been sparsely populated by nomadic peoples travelling across the Chilterns.

However, this all changed two thousand years later when husbandry of domesticated animals reached the Chilterns with sheep, cattle and pigs being farmed for protein-rich food. According to Julius Caesar, by the time of the invasion into lowland Britain in the first century BC most of the forests had been cleared for agriculture and most people were living in fortified settlements or oppidum.

All in all, we should thank our lucky stars that so many coincidences and unique events, against all the odds, played out in a particular way over a period of 14.8 billion years that we now find ourselves in a beautiful place in a great country, on the third rock from the sun. A ‘Goldilocks planet’ with just the right cocktail of elemental ingredients to create and sustain life was created when a star exploded and sprinkled its magic dust. We know all too well that our planet will only continue to be a sustainable place to inhabit if we choose to look after it. At present, science is digging us out of a hole with the present potentially catastrophic pandemic. But even if we fix the polluted planet and learn to conserve and recycle vital resources, we will need to raise our game if we are to survive the next crisis and every crisis that follows.

As Joni Mitchell sang in 1970. “…We are stardust! We are golden, and we’ve got to get ourselves back to the garden.”