A recent study by a team of scientists showed that nearly 100% of life was wiped out on Earth around 2 billion years ago, about 200 million years after the end of the Great Oxidation Event (GOE). This mass extinction event saw more of Earth’s biosphere killed off than the one that killed off the dinosaurs 65 million years ago.
The GOE was a time when Earth’s atmosphere and shallow oceans experienced a rise in oxygen. It started around 2.4 billion years ago and lasted until around 2 billion years ago. Micro-organisms developed the ability photosynthesise and started altering the chemical composition of the atmosphere. This increase in oxygen concentration provided a new opportunity for biological diversification and changes in the nature of chemical interactions between the various geological substrates, the air and water.
Ultimately, the abundance of oxygen-producing micro-organisms saw all the nutrients needed to create oxygen used up. These organisms died off from starvation. This led to a drop in oxygen levels which then killed off the other lifeforms that came to rely on oxygen for survival and reproduction.
And that is just the first atmospheric change event that we know of which caused mass extinctions. Subsequent mass extinctions were also widely believed to be caused by environment or climate changes brought on by geological processes or external factors such as impact events.
Right now, Earth is widely described to be undergoing the sixth mass extinction event right now. Human activities are the reason why millions of species, plants and animals included, are facing extinctions.
Large number of tropical forests are cleared to make way for our cities and other economical activities such as agriculture. On average, an estimated 18 million acres of forest are removed each year. Deforestations damage, if not destroy, the habitats in which animals live. Without proper shelter and the lack of food cause them to die off. This reduces our planet’s biodiversity.
Furthermore, deforestations reduce our planet’s ability to capture carbon from the atmosphere. When the fallen trees are left to rot or burnt, the stored carbon within are released back into the atmosphere. For example, the Indonesia forest fires of 2019 have released 360 million tonnes of carbon dioxide into the atmosphere, which is more than the carbon dioxide emission by Spain for the whole of 2018.
In addition to deforestation, our use of fossil fuels to power our vehicles, machines and electronics also releases carbon dioxide and other greenhouse gases such as sulphur dioxide and methane into the atmosphere. All these compounds trap heat close to the planet surface and cause global temperature to rise, which we come to know as global warming.
Global warming has been shown to be the main cause for the increase in the number of severe and intense weather events. There will also be an increase in number of hurricanes, typhoons, cyclones and tornadoes. Such disasters will cost us in terms of lives and resources such as money. Furthermore, rising sea levels will destroy many coastal regions and the communities that depended on it for survival. We will also get either very dry or very wet seasons across the tropical and equatorial regions. Heatwaves will be a common thing.
Food production will be affected with rising temperature. If there is no rain, we can’t grow rice, wheat or corn. Yields will fall dramatically, causing food shortages and exacerbate the divide between the rich and poor. Lifecycle of insects and pollinators such as bees , animals and plants will also be affected. Certain crops such as coffee, oranges and apples cannot grow if the climate is not right or when there are no pollinators around.
Furthermore, the oxygen levels in our atmosphere could be affected by this climate change.
As described earlier, oxygen did not play a part in the development of life early in Earth’s history until the evolution of organisms that can use carbon dioxide and solar radiation to produce energy and oxygen which we come to know as photosynthesis. This increase in oxygen ultimately led to diversification of life on Earth.
In modern era, we may think that land plants produced most of Earth’s oxygen but it has always been algae and marine microorganisms called phytoplankton that produced more than half of Earth’s oxygen. It is through their combined efforts that life could diversify and spread.
Since the oceans and seas are also warming together with our climate, it is causing a drop in dissolved oxygen levels. The excess carbon dioxide in the atmosphere will also be absorbed by the oceans over time that will cause them to be more acidic. All these environment changes will put extreme pressure on these algae and phytoplankton. If they are unable to adapt fast enough, they will die off en-mass. This will trigger a chain of events that ultimately affect our atmospheric composition and in turn, life on Earth as we know it. By then, it will be too late to do anything.
And who knows, one day we might just need to carry an oxygen tank behind our backs everywhere we go.