Note: this is an edited version of a piece I wrote for a writing competition earlier. Comments/critiques welcome!
One of the earliest known writing is the Sumerian cuneiform, dated about 3000 BC. The ancient Sumer civilisation was possibly the first to start recording events with linguistic content, using reeds to inscribe on moist clay tablets. Even earlier though, in the Cave of El Castillo, Spain, paintings by prehistoric Neanderthals dating back 40,000 years were discovered, making them the oldest known cave art in the world. These findings tell us of civilisations and societies long gone, fragments of evidence of their existence on this planet once upon a time. But we can go further back in time than that – the rocks on this planet tell a story too.
From geography lessons, most of us would know the three basic types of rocks: igneous, metamorphic and sedimentary. While igneous and metamorphic rocks contain information in their crystals as well, it is the sedimentary rocks, comprising 75% of the surface rocks on Earth, that give us a glimpse into the geological past. Even more remarkably, the fossils preserved within these rocks tell us of life before humans.
Imagine watching early analog television, with the box hooked up to an antennae that catches signals over the air. Every so often, the images blur, or static noise would appear on the screen, resulting in frustratingly fragmented snippets of the programme being screened. Thankfully, we now have digital television and other technological innovations that give us a smooth signal, allowing us to enjoy the latest episode of Big Bang Theory without a hiccup. The fossil record however, is like watching analog television – fragmented, capturing only brief snapshots of the environment and the life that existed at that point in time, though still reflecting the overall movement of time and space over the millions of years. It is difficult for most organisms to make it into the fossil record, and most that do are often disarticulated, reduced to bits and pieces over the millions of years.
There are however, sites of exceptional fossil preservation, known as fossil Lagerstätten, where living forms once lived and perished, and subsequently came to be buried. From the Ediacara Hills in South Australia, we came to know of the existence of the first multicellular, soft-bodied marine creatures that lived some 550 million years ago (Ma). A little further on in geological time, we discovered an explosion of phyla, broad biological groupings of organisms with the same basic body plan. This is the Burgess shale from British Colombia, Canada, showing us the soft parts of the hard-shelled marine organisms that were abundant about 505 Ma.
Life, as far as we know, originated in the oceans. How did humans come to dominate on almost all of the world’s land masses, alongside a mind-boggling variety of other organisms? The invasion of land happened several times, first by plants, then by arthropods like harvestmen, millipedes and insects, and finally by tetrapods, which by descent, all terrestrial vertebrates are. In Joggins, Nova Scotia, Canada, spectacular fossil findings of early tetrapods from about 310 Ma have been found, providing us with hints of how perhaps, a fish-like ancestor eventually evolved four limbs and slowly made its way onto land. Over time, a diversity of life forms emerged, some of which are still seen today. Over in Bavaria, Germany, a 147 million-years-old animal with feathers and the wishbone of a bird, but teeth, claws and a bony tail of a dinosaur was discovered. This is Archaeopteryx, possibly the ancestor to the ubiquitous birds we see and hear around us now.
Life has come a long way from its humble origins, and the sedimentary rocks speak of past catastrophes, dramatic climate changes, volcanic eruptions and tectonic shifts, even extraterrestrial influences. From fossil Lagerstätten, we see bizarre and unimaginable life forms that once upon a time, tread this same Earth that we are now on. Clearly, species have come and gone, with certain losses being of a global scale – so-called mass extinctions. It is the job of palaeontologists and geologists to fit the puzzles together, and find out what caused these decimations of life. Indeed, it is thanks to them that we now have a plausible idea of what might have caused the biggest mass extinction of all time. The Permo-Triassic mass extinction about 252 Ma resulted in a loss of an estimated 90% of all life on earth, possibly due to massive volcanic eruptions leading to global climate changes.
We are now entering a new geological period, the Anthropocene, with human impact being the key defining feature of the period, marked by another mass extinction and high atmospheric CO2 levels. As we continue to struggle with coming to terms with the consequences of our actions, our inertia and the positive feedback loop of our planet’s climatic system ensure a certainty of climate change in the future. Our forebears may not have had the privilege of insight that we now do regarding the sedimentary and fossil record. The rocks tell a story of upheaval and turmoil in the past – what story will the rocks be telling in millions of years’ time?