Imagine giant dinosaurs ruling the Earth... then suddenly, they're gone! Scientists have two main theories about what happened:
Theory 1: Asteroid Attack!
- A giant asteroid slammed into Earth 65 million years ago, creating a huge crater in Mexico.
- This caused massive explosions, wildfires, and dust clouds that blocked out the sun for years.
- Plants couldn't grow, so dinosaurs ran out of food and starved.
Theory 2: Volcanic Fury!
- In India, giant volcanoes erupted for hundreds of thousands of years, spewing hot gases and ash into the air.
- These gases caused the Earth to cool down and become acidic, making it hard for plants and animals to survive.
- The dinosaurs, who relied on plants for food, were among the many victims.
Who's Right?
Scientists are still debating this. Some think the asteroid might have contributed to the problem, but the volcanoes were the main culprit. Others believe the asteroid alone could have done it.
Here's the Twist:
- The asteroid hit 300,000 years before the dinosaurs disappeared!
- So, something else must have finished them off.
- Scientists think it was those long, super-powerful volcanic eruptions in India.
What's Next?
The mystery is still being solved. Scientists are studying rocks, fossils, and volcanic craters to figure out exactly what happened.
So, what can we learn?
- Even big and powerful creatures like dinosaurs can't survive extreme changes in their environment.
- Both asteroids and volcanoes can have huge impacts on Earth's climate and life.
Remember:
- Science is always working to answer these big questions.
- The more we learn about the past, the better we can understand our future.
----------------------------------------------------------------------------------------------------------------------
Complicated Version
How did dinosaurs disappear?
There are two popular explanations:
[1] Asteroid
A single, gigantic asteroid slammed into Earth 65 million years ago, wipping out dinosaurs and many other species. The asteroid plunged into Mexico's Yucatan Peninsula to carve out the Chicxulub crater. The impact triggered a worldwide environmental catastrophe expelling vast quantities of rock and dust into the sky, unleashing giant tsunamis, sparking global wildfires and leaving Earth shrouded in darkness for years.
Professor Ken MacLeod at University of Missouri-Columbia found evidence for this notion by examining the rock sediments drilled from five sites at the bottom of the Atlantic Ocean.
[2] Volcanic Eruptions
The dinosaurs died gradually from climate change caused by a series of severe volcanic eruptions in India at the end of the Cretaceous period, says Gerta Keller, professor of geosciences at Princeton University. This theory contradicts the long-held notion that the dinosaurs died due to climate change when a giant meteor hit the Yucatan region of Mexico.
Keller's theory has not yet been adopted by the broader scientific community. The most significant finding is geologic evidence that the mass extinction and the impact of the giant meteor occurred at two different times.
"The Chicxulub impact hit the Yucatan about 300,000 years before the mass extinction that included the dinosaurs and therefore could not have caused it," Keller says. "We know the age of impact because my team discovered a layer of tiny glass melt-rock spherules in Mexico and Texas." The spherules formed when the rocks were vaporized by the impact and blown into the stratosphere--and then rained down over North and Central America. "This glass spherule layer marks the precise time of the impact 300,000 years ago," she notes.
The sediments and fossils in the older sediments below the spherule layer and younger sediments above it reveal how life was affected by the impact.
"We see no change, not a single species died out, so the mass extinction 300,000 years later must have been caused by another catastrophe," Keller says. She's firm in her belief that the other catastrophe was a series of volcanic eruptions in the Deccan Traps, a volcanic mountain range that covers much of India today. The mountains, which today are 12,000 feet high, were much higher in prehistoric times.
"Volcanic eruptions poured out lava flows after lava flows, stacking them like a layer cake," she says. "The total volume in cubic miles was greater than the Rockies and the Sierras combined."
Related research by volcanologists Vincent Courtillot, Steve Self, Mike Widdowson, and Anne Lise Chenet shows the lava eruptions were not continuous but occurred in pulses, with each pulse lasting about 10--to at most 100--years, and the pulses were separated by short time periods of quiescence. New results from eight subsurface cores drilled by the Oil and Gas Corporation of India in the Krishna-Godavari Basin of eastern India reveal that at least nine lava flows mark the critical volcanic phase that ended in the mass extinction. This ending phase may have occurred over as little as 10,000 to 100,000 years. For each lava eruption, fire shot in tall columns from fissures in the Earth's surface and lofted gases into the stratosphere while the oozing lava spread sheet-like, or in rivers, up to 650 miles across India, and formed the longest lava flows on Earth.
"Their destructive nature is evident in the marine life record, which decreased by about 50 percent after the first of these long lava flows," Keller said. "By the time of the last lava flow, the mass extinction was complete."
The sulfur dioxide gas injected into the stratosphere converted to sulfate aerosols that caused climate cooling. The cooling lasted until the sulfate aerosols washed out as acid rain and caused the ocean to acidify in the process.
Research on smaller and more recent eruptions, such as the Laki eruption of Iceland in 1783-1784, clarified for scientists the extreme climate effects of volcanic eruptions and the resulting death and destruction of humans, animals, plants and marine life. In spite of the widespread devastation caused by Laki, mass extinction did not occur. The more recent example of Mt. St. Helen's in Washington State has shown just how quickly a local ecosystem can come back after a volcanic eruption.
Then why did it take Earth's ecosystem half a million years to fully recover after the mass extinction that killed the dinosaurs?
"The answer seems to be the occurrence of at least four additional massive Deccan eruptions about 280,000 years after the mass extinction," Keller says. "After those final eruptions, Earth began a full recovery leading to the evolution of life as we know it."
Keller doesn't disagree with scientists who believe the Chicxulub impact affected climate. The event would certainly have caused earthquakes, tsunamis, regional fires and injected huge quantities of sulfur dioxide into the stratosphere, causing cooling and acidification of the land and oceans. "The difference is that the quantity of gas injection from the main phase of Deccan eruptions was 30 to 100 times larger than the Chicxulub impact and occurred over as little as 10,000 to 100,000 years, with each pulse lasting about 10 years or more."
Up until now, skeptics have doubted whether gas from Deccan-like eruptions reaches the stratosphere, but the relatively small 1783-1784 Laki eruption in Iceland revealed that even rather small eruptions loft gases into the stratosphere.
Until recently, it was also believed that the last phase of Deccan volcanic eruptions occurred over a million-year period, which would have been long enough for the environment to recover between eruptions, thus preventing a runaway extinction effect. Vincent Courtillot and collaborators from the Institut de Physique du Globe de Paris have recently discovered that the main phase of Deccan eruptions was much shorter and culminated near the Cretaceous-Tertiary boundary. Known as the "K-T boundary" to scientists, it marks the end of the Mesozoic Era and is associated with the mass extinction.
Most importantly, field work by Keller and her collaborators revealed that the mass extinction coincided with the end of the main phase of Deccan eruptions suggesting that volcanism is the "smoking gun" that killed the dinosaurs.
Reference
Volcanoes, Not Asteroid, May Have Taken Out the Dinosaurs
The National Science Foundation October 2009
The National Science Foundation October 2009
Single massive asteroid wiped out dinosaurs: study Reuters Nov 30, 2006
Study: Single Meteorite Impact Killed Dinosaurs LiveScience.com Nov 28, 2006
