Question

The hypothesis that an impact killed the dinosaurs seems (a) well supported by geological evidence; (b) an idea that once made sense but now can be ruled out; (c) just one of dozens of clear examples of impacts causing mass extinctions.

Short answer

Option (a) is correct; the hypothesis is well supported by geological evidence.

Step-by-step solution

Understanding the Question

The task is to choose between different interpretations of the hypothesis regarding the impact that killed the dinosaurs. We need to evaluate each option in the context of current scientific understanding.

Evaluating Option (a)

Option (a) suggests that the hypothesis is well supported by geological evidence. The hypothesis of an asteroid impact is still widely supported due to evidence such as the Chicxulub crater and a layer of iridium-rich clay found worldwide, matching the timeline of the dinosaur extinction.

Evaluating Option (b)

Option (b) presents the hypothesis as outdated or no longer valid. This contrasts with the scientific consensus, which still considers an impact as a plausible explanation for the mass extinction event 66 million years ago.

Evaluating Option (c)

Option (c) states that the hypothesis is one of many examples of impacts causing mass extinctions. While there may be other extinction events with different causes, the dinosaur extinction is the most cited example of an impact causing a mass extinction, making this option less precise.

Determining the Best Option

Considering the current scientific evidence and consensus, option (a) is the most accurate. Geological evidence supports the hypothesis of an impact event significantly contributing to or causing the extinction of the dinosaurs.

Key concepts

Asteroid Impact Hypothesis

The Asteroid Impact Hypothesis suggests that a massive asteroid collided with Earth around 66 million years ago. This catastrophic event is believed to have led to the sudden extinction of the dinosaurs. The hypothesis was first widely discussed in the 1980s. It postulates that the impact released an immense amount of energy, equivalent to billions of atomic bombs. Such a powerful collision would have resulted in massive wildfires, tsunamis, and an "impact winter," where dust and particles thrown into the atmosphere blocked sunlight. This, in turn, would have caused a drastic drop in global temperatures, disrupting photosynthesis and collapsing food chains.

Scientists believe that this chain reaction led to the extinction of approximately 75% of Earth's species at the time. While it's not the only explanation for the extinction of dinosaurs, it remains the most widely supported hypothesis due to substantial geological and fossil evidence.

Geological Evidence

Geological evidence strongly supports the Asteroid Impact Hypothesis. One of the most noteworthy pieces of evidence is a worldwide layer of clay enriched with iridium. Iridium is a rare element on Earth's crust, but it is abundant in asteroids and comets.

This iridium layer is found in sedimentary rocks at the Cretaceous-Paleogene (K-Pg) boundary, which dates back to about 66 million years ago. This timing matches the extinction of the dinosaurs. The presence of such a distinctive layer indicates a significant event, as the iridium could have only been deposited from an extraterrestrial source.

Furthermore, there are shocked quartz deposits found around the globe. These are formed under high pressure during meteorite impacts, further supporting the impact hypothesis. These geological markers collectively strengthen the case that a colossal asteroid impact was responsible for the dinosaurs' extinction.

Mass Extinction Events

Mass extinction events are periods in Earth's history when large numbers of species rapidly died out. These events have profoundly changed the course of life on our planet. While there have been five major mass extinction events, the one that wiped out the dinosaurs is perhaps the most famous.

Scientists study mass extinction events to understand Earth's biological past. They examine various causes, such as volcanic eruptions, climate change, and asteroid impacts. Each event has its unique set of circumstances, amounting to complex puzzles that scientists piece together using fossil records and geological evidence.

The end-Cretaceous mass extinction event, which correlates with the asteroid impact, showcases the dramatic effect such catastrophic events can have on Earth's biodiversity. This research not only helps us understand past events but also raises awareness of current biodiversity threats and the potential impacts of future events.

Chicxulub Crater

The Chicxulub Crater, located on the Yucatán Peninsula in Mexico, is a key piece of evidence for the Asteroid Impact Hypothesis. It is about 180 kilometers in diameter, making it one of the largest confirmed impact craters on Earth.

Discovered in the late 20th century, the crater aligns with the K-Pg boundary both in age and in geological characteristics connected to asteroid impacts. The discovery was a pivotal moment in confirming the asteroid impact theory, supporting the notion that an asteroid hit Earth with enough force to cause massive destruction.

Studies of the Chicxulub Crater have shown evidence of immense heat and pressure, typical signatures of impact events. This massive crater is not just crucial for understanding the extinction of the dinosaurs but also offers critical insights into how catastrophic events can reshape Earth's ecosystems in profound ways. The ongoing research into the Chicxulub Crater advances our understanding of planetary science and Earth's history.