Introduction

Earth took shape roughly 4.6 billion years ago and remains, as far as we currently know, the only life-supporting planet - its surface carries landforms such as mountains, plateaus and glaciers, and its living organisms exist within a thin, complex zone called the biosphere. The living world holds wonders that aren't always obvious at first glance but grab attention once noticed: a sunflower turning to track the sun, a firefly's flashes lighting up a dark forest, water droplets beading and rolling off a lotus leaf, the sudden snap-shut of a Venus flytrap's leaf when touched by an insect, or a squid squirting ink to throw off a predator. Such examples show that this planet's wonder lies in both its non-living landforms and its living forms existing side by side. Underlying much of this is the DNA molecule - built from carbon, hydrogen, oxygen, nitrogen and phosphorus - which governs and regulates life itself, a shared thread linking the living and non-living components of the planet. A 2011 survey by Mora and colleagues estimated the number of species on Earth at around 8.7 million, spanning microbes, plants, animals and human beings, each carrying its own unique and distinguishing characteristics.