January 29, 2018
The non-humans I work with are neither plants nor animals: they are unicellular organisms, belonging to the kingdom of Protista. Foraminifera, as they are called, inhabit our seas and oceans and even though they are small, they are capable of creating a little house: a teeny-tiny shell, made of calcium carbonate. Even though this Glossy is about the future of the Zoo, I would like to share a story of the past, a climate history told by these tiny shells.
Before thinking about the meaning of (the Zoo in) the Anthropocene, we need to put this proposed geological epoch into the context of the geological timescale, where it might -or might not- belong someday. Before thinking about the place of humans, other animals and plants in the Zoo it might be useful to look at their first appearances, in non-human, non-animal, non-plant timescales.
The geological timescale is dividing the history of the planet in era’s which are subdivided in periods, epochs and ages, based on the strata -layers of rocks- that can be found back below our feet, containing the fossil remnants of organisms long gone extinct and chemical substances to guide us back through time. The time units of the geological time scale are precisely defined by the International commission on stratigraphy. The Anthropocene has not been officially accepted.
The timescale starts with the birth of our planet, roughly 4,6 billion years ago. The young Earth was not yet very hospitable to life: no seas, no water, no free oxygen and meteorites bombarding the surface. Even though we do not know yet exactly understand how, we know that life evolved relatively soon, around 4 billion years ago. Gradually the atmosphere became more oxygenated through the invention of photosynthesis and to short-cut the story a bit: this facilitated the evolution of more complex life forms. 500 million years ago, during the Cambrian, there was a sudden explosion of complex life forms known as the Cambrian radiation. Organisms with bodies came and shells, such as foraminifera, evolved around this time. Carnivory, an energy consuming business requiring oxygen, was also invented. This possibly accelerated the need for an evolutionary arms race, including the evolution of hunting aids (eyes for vision and teeth to eat your prey) and protection techniques (becoming invisible by adjusting your color and creating a shell to hide in). During the Triassic, around 230 million years ago, the Dinosaurs appeared, and they roamed the earth for a relatively long time and even survived a mass extinction at the Triassic-Jurrassic boundary. Eventually they were also wiped out, probably due to the impact of a large meteorite and massive volcanic eruptions. And then, only half way the Quarternary, early human like species evolved, with Homo sapiens arriving 300.000 years ago.
How does the International commission on stratigraphy decide on the definition of a geological era or epoch? Geologists base these periods on species assemblages, preserved as fossils in the rocks. Species have evolved and vanished with the many changing climates and catastrophes the Earth has faced. The boundaries between time units of the Geological timescale are therefore often defined by mass extinctions.
The earth has thus seen different climates throughout its history. Yet how do we know this, how can you measure the temperature of the past? Paleoclimatologists try to reconstruct the temperature of the seawater from indirect measurements on foraminifera that are preserved at the bottom of the sea. The chemistry (stable oxygen isotopes ratios and trace metal content) of the calcite shells provides us with an estimate of the seawater temperature and ice volume covering the Earth during the time these organisms were living.
And they discovered, that in the past, it has been much warmer. During the Eocene it was around 12 degrees warmer, crocodiles were literarily swimming around Antarctica. Gradually, it became colder again and Antarctica ice sheets started to grow. 2,8 million years ago, also the Northern Hemisphere became glaciated. Since then, the Earth has been in an Ice Age, with ice sheets waxing and waning paced by the orbital wiggles of the Earth and the planets orbiting the Sun. At present we are in an interglacial, the Holocene, meaning we are in a warmer period between two glacials. Temperatures now however, are changing faster then they did in the previous 800.000 years. Looking at carbon dioxide levels, which were always paced with interglacial / glacial levels and driving temperatures, have been shooting up, at an unprecedented speed. To compare this to anything, we have to go back to carbon dioxide levels of the Eocene, which was a very different world with high sea level and the crocodiles, so… not that comparable after all. If it turns out that we humans have reached a tipping point in the current climate system and prevent the next glacial to even start, we are not in an inter-glacial time period, yet at the end of an ice house and the beginning of a hot house Earth.
Lets go one step back and look further in how you can unravel all these interesting climate wiggles and how this involves my own work at the Royal Netherlands Institute for Sea research (NIOZ). In order to go back in time we embark our ship the Pelagia and take cores of seafloor sediments from all over the world. The deeper we go into the seafloor, the deeper we go in time (depending on the sedimentation rate). We hope to encounter nicely layered sediments that have been deposited in chronological order. However, sometimes we also encounter cores that look like marble cakes or slush puppies.
There a lot of interesting features in these sediment cores, such as desert dust, organic geochemistry and element ratios that can be studied. I mainly sieve out the foraminifera. There are many different species and they come in many marvelous shapes. Remember that it’s just the cell of a unicellular organism creates these shells! During their life, they eat and grow, just like us, and add another chamber to their shell every time they need a bigger house. Adding new chambers according to some kind of genetic algorithm results in these beautiful patterns. And this is what actually fascinates me the most. Because how can these single cells, create these architectural marvels? To better understand how the chemistry of these shells records the climate of the past, we need to better understand what kind of chemistry foraminifera use themselves, when building their shell. This is what I’m trying to unravel, together with other scientist, and this is where chemistry and biology, matter and life, meet.
Artist impressions of mass extinctions often show a chaotic event, a seemingly clear boundary: a big meteorite appears in the sky, a big impact follows and then every creature dies. However, mass extinctions do not necessarily happen over night. A mass extinction might take ten thousands of years, whereby a gradual change of the environment (like gradual warming, or gradual cooling) causes the gradual extinction of species.
So to come back at the Anthropocene: the idea that we modern humans have created a new geological period, might be a rather anthropocentric, or human-scale perspective. From a geological perspective we might say that we humans are now shaping a boundary between geological periods, dividing the Quarternary from a new geological era. Yet this can only be decided the future members (robots?) of the International commission on stratigraphy that have evolved after the 6th mass extinction.