Extinction: Past and Present — Reading Comprehension

Extinction is the complete disappearance of a species from Earth. Scientists have identified extinction as a key process that has shaped life throughout Earth's history. Over millions of years, countless species have vanished, while new ones have evolved. Today, scientists use evidence from fossils and genetic studies to understand the causes and patterns of extinction. These studies reveal that extinction is not just a thing of the past—it is a process still happening today, often at an accelerated rate.

How Extinction Happens

The normal, slow rate at which species go extinct is called the background extinction rate. This rate is usually balanced by the formation of new species. However, sometimes extinction rates rise sharply during events known as mass extinctions. Scientists have identified five major mass extinction events, including the Permian extinction, which wiped out over 90% of marine life, and the Cretaceous extinction, which led to the disappearance of the dinosaurs about 66 million years ago. Causes of extinction can include drastic environmental changes such as volcanic eruptions, asteroid impacts, climate shifts, and competition with other species. Disease and the loss of habitat also play important roles. By analyzing rock layers and fossil records, scientists can trace how these factors contributed to waves of extinction across time.

Extinction in the Modern World

Today, the rate of extinction is 100 to 1,000 times higher than the background rate—a situation scientists call the biodiversity crisis or the "sixth mass extinction." Many species are threatened by human activities like deforestation, pollution, overhunting, and climate change. Recently extinct species include the thylacine, a striped marsupial from Australia; the golden toad of Costa Rica; and the Baiji dolphin from China. Scientists monitor endangered species and use data to predict which ones are at risk. Preserving biodiversity is crucial because each species plays a role in its ecosystem, contributing to functions like pollination, nutrient cycling, and food webs. Losing species can upset these systems and even affect humans by reducing potential medicines, crops, or ecosystem services.

The Importance of Preventing Extinction

Preventing extinction matters for many reasons. Every species has intrinsic value and may provide benefits to humans or ecosystems that we do not yet understand. Conservation efforts, like protecting habitats and endangered species, help maintain the stability and resilience of ecosystems. Scientists and policymakers work together to reduce threats and restore populations, using technology, laws, and education. Understanding extinction helps us see our role as part of Earth's interconnected web of life and encourages responsible stewardship of the planet.

Interesting Fact: About 99% of all species that have ever lived on Earth are now extinct, showing how life is constantly changing and evolving.

What is extinction?

What does the term 'background extinction rate' mean?

Which event caused the extinction of the dinosaurs?

What is an ecosystem?

Which of the following is NOT a cause of extinction mentioned in the passage?

What does 'biodiversity crisis' mean as used in the passage?

Why is preventing extinction important according to the passage?

How do scientists study extinction?

True or False: The thylacine, golden toad, and Baiji dolphin are all recently extinct species.

True or False: Mass extinctions have only happened once in Earth's history.