Sixth Mass Extinction
About more than 99 percent of all the organisms that have ever lived on Earth are now extinct. As the newer species evolve to fit in the ever-changing ecological niches, the older species fade away. However, the rate of extinction is much far from the constant. About more than a couple of times in the last 500 million years, 75 per cent to more than 90 percent of all the species on Earth have been disappeared in the geological blink of an eye in several catastrophes that we call mass extinctions. Though the mass extinctions are deadly events, they help to open up the planet for the newer forms of life to emerge. The mass extinction that was studied the most, that remarked a boundary between the periods of Cretaceous and Paleogene around 66 million years ago, had killed the nonavian dinosaurs and eventually made space for the mammals and the birds to rapidly diversify and gradually evolve. In this article, we will discuss about the mass extinction, the sixth mass extinction, the mass extinction definition, and the mass extinction events.
5 Mass Extinctions
The 5 mass extinction events include the following:
The Ordovician - Silurian Extinction
During this extinction, the life of the small aquatic organisms was ended. This happened around 440 million years ago. 60% of the animal species were extinct in this period.
The Devonian Extinction
This marks the extinction of the tropical marine life forms. This extinction occurred about 20 million years ago. 70% of the marine species which included the coral reefs were extinct in the shallow regions of the sea.
The Permian - Triassic Extinction
This is the largest mass extinction that is known that depleted a huge range of species, including the vertebrates. It was an abrupt extinction. 96% of the marine and the terrestrial animal species were extinct and hence this event is referred to as the Great Dying. It is known to be a result of a huge volcanic activity or the comet that struck the surface of the earth.
The Triassic - Jurassic Extinction
This extinction took place about 18 million years ago during the end of the Triassic age. All the terrestrial and marine reptiles and the plant species which included the dinosaurs were all wiped out.
The Cretaceous-Tertiary Extinction
This marked the extinction of the nonavian dinosaurs. They were all wiped out at the end of the Cretaceous period and during the beginning of the Tertiary period. Therefore, it is called the KT extinction. It marked the dawn of a new era and age. The extinction took place about 65 million years ago when a huge asteroid hit the surface of the earth. This, in turn, led to immense changes in the atmosphere, the sea levels and the temperatures that ended life on the surface of the earth.
Sixth Mass Extinction
We are at present in the middle of the sixth mass extinction, and humans are the big cause of it. The humans have already killed most of the several animal species for their own recreational activities and benefits.
The invasive species were previously transported from one part of the world to the other part that eliminated the native species that resided in that part. Also, the immigration and the emigration of the humans and the animals have spread several diseases in several different parts of the world wherein they were not present before.
The toxic chemicals have harmed marine life to a greater extent. The natural available resources are also depleting to a wider extent because of the growing population. The heavy pollution has led to an increase in the temperatures and the water levels in the sea that would have several catastrophic effects on life on the earth in the coming future.
Mass Extinction Causes
The changes in the sea levels have changed the salt and the oxygen concentration in different parts of the earth’s oceans. The changes in the sea levels have disturbed their habitats and that led to the extinction of several species.
The meteorite attacks that happened on the earth, the anoxic conditions, and the volcanic activities all led to the extinction of a huge mass of the animals in the Permian-Triassic extinction. The meteorites that have fallen on the earth had a catastrophic effect on the planet.
The increase in the temperatures had led to the melting of the glaciers and hence an increase in the sea levels.
FAQs on Mass Extinction
1. What is a mass extinction event as per the NCERT syllabus?
A mass extinction is a widespread and rapid decrease in the biodiversity on Earth. According to the fossil record studied in the NCERT syllabus, it is an event where a significant percentage of the world's species, often more than 75%, are wiped out in a geologically short period. This is different from the normal, ongoing rate of species loss, known as background extinction.
2. What are the 'Big Five' mass extinctions in Earth's history?
The five major mass extinction events, often called the 'Big Five', are key examples of large-scale biodiversity loss in Earth's history. They are:
- Ordovician-Silurian Extinction: About 443 million years ago, caused by a severe ice age, wiping out many marine organisms.
- Late Devonian Extinction: About 360 million years ago, a prolonged climate change event that devastated life in shallow seas.
- Permian-Triassic Extinction: About 252 million years ago, the most severe event, also known as 'The Great Dying', which eliminated over 90% of all species.
- Triassic-Jurassic Extinction: About 200 million years ago, volcanic activity led to the extinction of many large amphibians and reptiles, allowing dinosaurs to flourish.
- Cretaceous-Paleogene Extinction: About 66 million years ago, famously caused by an asteroid impact that led to the extinction of the dinosaurs.
3. What was the most severe mass extinction, and what caused it?
The most severe mass extinction event ever recorded was the Permian-Triassic extinction, which occurred approximately 252 million years ago. It is often called 'The Great Dying' because it wiped out about 96% of marine species and 70% of terrestrial vertebrate species. The primary cause is linked to massive volcanic eruptions in the Siberian Traps, which released enormous amounts of carbon dioxide, leading to extreme global warming, ocean acidification, and lack of oxygen (anoxia) in the seas.
4. What are the common causes identified for past mass extinctions?
Scientists have identified several major causes for the mass extinctions in Earth's history. These catastrophic events are often triggered by one or a combination of the following factors:
- Massive Volcanic Activity: Large-scale eruptions release greenhouse gases, causing rapid climate change.
- Asteroid or Comet Impacts: The impact of a large celestial body can cause widespread devastation and block sunlight, leading to a collapse of food chains.
- Rapid Climate Change: Both severe ice ages (global cooling) and intense global warming events have been major drivers of extinction.
- Changes in Ocean Chemistry: Events like ocean anoxia (lack of oxygen) and acidification can decimate marine life.
5. How is a mass extinction different from a background extinction?
The key difference lies in their rate and scale. Background extinction refers to the normal, continuous, low-level extinction of species that occurs over time as a result of natural ecological and evolutionary processes. In contrast, a mass extinction is a catastrophic event where the rate of extinction increases dramatically above the background rate for a short geological period, affecting a large and diverse range of species on a global scale.
6. What is the significance of mass extinctions for the evolution of new life forms?
Mass extinctions play a crucial role in shaping the path of evolution. By wiping out dominant species, they open up previously occupied ecological niches. This creates an opportunity for surviving species to undergo adaptive radiation—a rapid diversification into new forms to fill these vacant roles. For example, the extinction of the dinosaurs allowed mammals, which were small and marginal before, to diversify and eventually become the dominant terrestrial vertebrates.
7. Are we currently experiencing a sixth mass extinction, and what makes it different?
Many scientists believe we are currently in a sixth mass extinction, often called the Holocene or Anthropocene extinction. What makes this event unique is its primary cause: human activities. Unlike past extinctions driven by natural geological or cosmic events, the current crisis is fueled by habitat destruction, climate change, pollution, and overexploitation of species. The rate of extinction today is estimated to be hundreds of times higher than the natural background rate.
8. How do scientists use the fossil record to identify a mass extinction event?
Scientists identify mass extinctions by studying layers of sedimentary rock, known as strata. A mass extinction event is clearly visible in the fossil record as a distinct boundary where a large number of species' fossils abruptly disappear from the rock layers above. For instance, the Cretaceous-Paleogene boundary is marked by the sudden disappearance of dinosaur fossils. This boundary often contains unique geological evidence, such as a thin layer of iridium, a rare element on Earth but common in asteroids, which provides a 'smoking gun' for an impact event.
