jouw wetenschapsgids in de hoofdstad

jouw wetenschapsgids in de hoofdstad

8 Ways the universe might kill us – Part 1: Mass Extinctions

We humans tend to take our existence for granted. Some of us have even become comfortably numb: In the middle of the night we can get something to eat at a nearby frituur or kebab shop. Even though it’s raining fiercely, we sleep underneath a roof and a warm blanket. Even if we lose our job, the government (or at least our friends) can help us out. Current conditions for life belong to the most stable since the existence of mankind. All of this gives us a blind assurance that the future will not differ much from today. Physicist Lenka Zychova would like to rid us of this illusion with this eight part series on the different ways life on Earth could be suddenly extinguished. The first part will tackle mass extinctions. Life on Earth came perilously close to going extinct no less than five times.


 

The Earth is about 4.5 billion years old, of which the last 3.8 billion years life is decorating its puddles and rocky bits. At first, life on Earth was quite simple, just some micro-organisms happily bathing in the oceans. Four billion years later, life is still here!

Our beautiful, lively planet is also a cemetery for 99% of the species that once enjoyed their existence here.

A closer look at the data however, confronts us with the fragility of life on Earth. It is estimated that at present, the Earth is home to less than 9 million different species of animals. But in the whole history of life on Earth there were about 5 billion species! This means that our beautiful, lively planet is also a cemetery for 99% of the species that once enjoyed their existence here. How is this possible? And above all, is there an extinction-threatening apocalypse looming, a spectacle for which humanity will have front seat tickets?

The extinction of organisms is occurring more or less continuously. Some species are simply unable to adapt to climatic or other changes in time. Swift environmental changes, such as temperature or sea level changes, which are sudden and very intense, can cause chain reactions, hitting large populations in the animal and plant kingdoms. Life on Earth has experienced such massive extinctions at least five times. The most famous of them is associated with the extinction of the dinosaurs at the end of the Cretaceous, about 65 million years ago. At that time, over 70% of all animal and plant species on Earth died.

The most massive extinction occurred about 250 million years ago, when up to 96% of all organisms died.

The most massive extinction occurred earlier, about 250 million years ago, when up to 96% of all organisms died. The Permian Extinction started with extensive lava flows, covering an area of two million square kilometers in what we now know as Siberia. The darkness caused photosynthetic plants, dependent on light to produce their energy, to die. Those who survived were later destroyed by the great drought and heat caused by the greenhouse gases expelled into the atmosphere by all this volcanic activity. This in turn led to increased evaporation of water, spectacularly dropping the sea levels and increasing salt concentration in the oceans. So while land animals died of starvation and lack of oxygen, the increased salinity of ocean water spelled doom for billions of marine organisms.

Pangaea_continents

Map of Pangaea showing where today’s continents were during the late Permian. Source: Wikimedia, Creative Commons

We do not have to fear the complete extermination of mankind as a result of a super volcano having a temper tantrum. However, a collision with a cosmic body can also make our day very unpleasant.

We don’t expect similar drastic lava flows at present, so we do not have to fear the complete extermination of mankind (and all other life on Earth) as a result of a super volcano having a temper tantrum. However, a collision with a cosmic body can also make our day very unpleasant. The dinosaurs were not terribly excited about a ten-kilometer wide asteroid hitting the Earth. The interplanetary body crashed into the Earth’s atmosphere at about 70,000 km/h, compressing and heating the air to thousands of degrees Celsius , and struck with the energy of billions of Hiroshima bombs in the area of today’s Yucatan Peninsula. The pressure wave relentlessly swept away all living creatures within thousands of kilometers. An enormous amount of debris was thrown into the sky and created a secondary shower of impacts, which then expanded the affected area. Dust in the atmosphere formed an impenetrable layer for sunlight, and therefore hit the base of the food chain. Furthermore, the asteroid had chosen a perfect place for its kamikaze action – it fell into a site of carbonated rocks, rich in sulfur and other elements, that evaporated and later formed acid rain, wiping out vital marine life.

 

Chicxulub_how it looked after the impact_ Credit Detlev van Ravenswaay

Artist’s impression of the impact crater of the asteroid that caused the fifth mass extinction. Credit: Detlev van Ravenswaay

This extinction at the end of the Cretaceous is also associated with massive volcanism happening on the other side of the globe, in today’s India. There are intriguing suggestions that the seismic waves, which spread after the Yucatan Impact, circulated the Earth and collided in an area where we now find vast layers of solidified lava, the so-called Deccan Traps. The interfering seismic waves would have sustained and intensified the volcanic activity that had already taken place in that region. However, this hypothesis has not yet been confirmed. Whether the impact itself was enough to destroy most of the population at that time, or volcanic blasting was what tipped the extinction over the edge, a collision with an asteroid is a major threat to us as well. How likely this catastrophic event is nowadays, will be discussed in the second episode of this series.

Deccan Traps in Western India. Credit: Mike Widdowson

Humanity is well on its way to cause a sixth mass extinction on Earth.

Even so, we might not need an asteroid or any external cause for an extinction. In fact, humanity is well on its way to cause a sixth mass extinction on Earth. Billions of wildlife populations have been lost in recent decades due to human overconsumption and pollution. Eventually, though, humanity will pay a high price. Plants, animals and micro-organisms provide us with essential ecosystem services, such as crop pollination, sea food supply, a liveable climate, clean air, clean water etc. Action to stop this human-caused mass extinction remains possible, but it cannot be delayed any longer. On that bombshell, we’ll sign off for now. And speaking of bombshells, we hope to see you at the end of April for the next instalment in this series: asteroid impacts!

Featured image: A quarter of a billion years ago, long before dinosaurs or mammals evolved, the 3 meter predator Dinogorgon hunted floodplains in the heart of today’s South Africa. Dinogorgon vanished in the Permian extinction, along with about nine of every ten plant and animal species on the planet. Credit: Jonathan Blair – National Geographic.