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15.2Chapter 15: The Earth in Space (Universe and Stars)

Collisions, asteroids, and mass extinctions — Alhussan Physics - Stage 9 Revision Notes & Topical Questions

5 min read 8 parts Lesson 2 of 6 1 quiz

📚 Alhussan Physics - Stage 9 Hub / Topical Revision
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Physics 15.2 Collisions, asteroids, and mass extinctions — Chicxulub Impact and Earth's History — Alhussan International Academy — Physics (Stages 7–9) notes: Describe the evidence for asteroid collisions and some consequences of asteroid impacts.Orbit changes — Jupiter's gravity…

  • Collision course
  • Past impacts
  • Craters on Earth
  • Meteorites
  • Why fewer on Earth
  • Vaporising

Part 1 of 6Why asteroids collide with planets

Orbit changes
  • Jupiter's gravity can pull asteroids out of their orbit in the asteroid belt.
Collision course
  • Their new direction may take them on a path towards the Earth.
Past impacts
  • Very many asteroids have collided with objects in the Solar System in the past.

Part 2 of 6Evidence for impacts

The Moon
  • It is covered in millions of craters, and conditions on the Moon keep them visible.
Craters on Earth
  • Some are visible, such as Meteor Crater in Arizona formed by a 40 m piece of iron, and the Lonar crater in India, now a lake.
  • Some craters are only visible from space.
  • The crater of the asteroid that may have killed the dinosaurs lies deep off the coast of Mexico and was not discovered until 1978.
Meteorites
  • They provide further evidence of asteroids hitting the Earth.
Why fewer on Earth
  • Weather, water and plate movements erase craters.

Part 3 of 6What happens in an impact

Vaporising
  • The ground and the asteroid can be vaporised, throwing dust, ash and gas into the air.
Ocean impact
  • An asteroid hitting an ocean can cause a tsunami.
Crater size
  • A large metallic asteroid hitting soft rock makes a large crater, and a 50 m asteroid can make a crater over a kilometre wide.
Dependence
  • The effect depends on what the asteroid is made of and what it hits.

Part 4 of 6Impact winter and mass extinction

Climate balance
  • The climate depends on the balance between energy arriving from the Sun and energy the Earth radiates into space.
Impact winter
  • Dust from a very large asteroid blocks sunlight and the temperature falls quickly.
  • Plants that need photosynthesis die, then the animals that eat them.
  • An impact winter lasting over a year would make it difficult for humans to survive.
Mass extinction event
Mass extinction event an event that causes 75% to 90% of all species to disappear in a relatively short time.
  • They happen on average about every 25 million years.

Part 5 of 6The dinosaurs and other extinctions

Dinosaurs
  • About 66 million years ago an asteroid about 9 km across hit the Earth at Chicxulub in Mexico and probably killed most dinosaurs.
Other mass extinctions
  • Most are thought to result from climate change due to volcanic emissions or changes to the oceans.
Five events
  • The Earth has had five major mass extinctions, so the exact cause of an event is hard to know.

Part 6 of 6How often impacts happen

  • Dust
    • More than 100 tonnes of dust hits the Earth every day but burns up in the atmosphere.
Object sizeHappens about everyEffect
A car (5 m)YearA fireball
A football field (100 m)5000 yearsA large crater, significant damage, tsunami
Half a kilometre (about the tallest building)100 000 yearsClimate change, impact winter, possible mass extinction

Key terms

TermMeaning
CraterA bowl-shaped hole made by an impact.
Impact winterA rapid fall in temperature caused by dust blocking sunlight after a large impact.
Mass extinctionAn event in which a large percentage of species disappear in a short time.
TsunamiA giant sea wave, which can be caused by an impact in the ocean.
MeteoriteA piece of rock from space that reaches the ground.

Avoid these mistakes

1
Thinking all craters on Earth are easy to see — many are eroded or hidden.
2
Thinking an asteroid impact caused every mass extinction — most were caused by climate change from volcanoes or ocean changes.
3
Thinking an impact only damages the place it hits — dust can change the global climate.
4
Thinking the dinosaurs lived at the same time as humans — they died out about 66 million years ago.

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