Meteorites and the history of Earth

Meteorites are the solar system’s leftovers. They are material that did not get incorporated into forming planets or the debris left after a space collision. These leftovers can tell us a lot about Earth’s formation. 

What are meteorites? 
  • Meteoroids = rocks in space 
  • Meteors = space rocks falling through the atmosphere (‘shooting stars’) 
  • Meteorites = space rocks that have landed on Earth’s surface 
Meteorites hit the Earth with great force and large ones leave impressive craters that are much larger than the rock itself. 

This meteor crater in Arizona was made by the impact of a 30-50 m diameter iron meteor. The crater has a diameter of 1,200 m. (NASA Earth Observatory 2009, Public domain) 
Are there different types of meteorites? 
Yes! Meteorites have very different compositions and structures. The main types are:  
  • Iron: composed of 90% - 95% iron and nickel. The iron and nickel grow in interlocking crystals called Widmanstätten patterns. The meteorite must be cut, polished and etched to see these beautiful crystals. Iron meteorites make up approximately 5% of meteorites. They are thought to be the cores of asteroids that cooled slowly over billions of years. 
Pitted exterior of the Wyangle meteorite from NSW, an iron-nickel meteorite 

Widmanstätten patterns are visible on the polished and etched interior of the Wyangle meteorite 
  • Stony iron composed of roughly equal amounts of iron and stone, these are the rarest meteorites. Less than 2% of known meteorites fall into this category. These meteorites often contain precious and semiprecious gemstones.  
Large olivine crystals are visible in this section of a rare stony-iron meteorite 
  • Stony: made of silicate minerals. These are the most common type of meteorites and are made of rocks from the early solar system. These include chondrites (grainy meteorites) and achondrites (rock that melted and have a layered structure). 
This slice of a stony meteorite shows a typical grainy chondrite structure 


Meteorites photographed by S Filan from the WB Clarke Geoscience Centre, Londonderry NSW

Earth’s water came from meteorites! 
Getting water from rocks seems like a strange idea, but scientists believe that most of Earth’s water came from carbonaceous chondrites (rocky meteors with lots of carbon). These meteorites are rich in water and organic material. They helped to create our atmosphere and make Earth a place with conditions suitable for life. 


Determining Earth’s age using meteorites 
Scientists use radiometric dating to determine the age of rocks on Earth, however, rock gets weathered away and recycled by plate tectonics, making it difficult to find fragments of early Earth. Meteorites offer us the opportunity to date materials from our section of the Solar System, very likely of a similar age to Earth, to determine its age. The current best estimate is 4.56 billion years. 



Making your own craters 
How do we calculate the size of a meteorite from its crater? Was it a direct hit or did it come in on an angle? These and so many other questions can be answered through looking at the rocks but also through modelling. 

Model your own meteorite impacts at home. All you need is a tray or box, balloons, sand and a ruler. Just click here to download our PALMS activity and here for the guide (for more detail).  
Our very own impact crater