Small variations in the Earth's orbit dictate how much sunlight certain areas of the Earth get.Small variations in the Earth’s orbit dictate how much sunlight certain areas of the Earth get.

Wobbly Earth causes climate change, extinctions: researchers

Updated Fri. Oct. 13 2006 12:14 PM ET

Brian Jackson ,

Earth’s orbit isn’t perfect. In fact, it’s as wobbly as a beach ball floating in a swimming pool, says the latest research. Now scientists are blaming the imperfect orbit for the extinction of ancient Spanish rodents.

There are a number of ways the Earth’s orbit can vary. Its shape around the sun can be more or less circular, or the tilt of the poles in relation to the Sun can change, for example. These small variations can last for tens of thousands to millions of years.

Variations like this transform the Earth’s climate by altering the sunlight available in different parts of the planet. Scientists have supposed this could lead to an impact on life, but couldn’t prove it until now.

Researchers from Utrecht University in the Netherlands conducted a study on Spanish rodent fossils from central Spain. Over 80,000 teeth were used to date the fossils – ranging from 2.5 million to 24.5 million years old – and chart fluctuations in the rodent’s population.

The population rates correlated with the history of Earth’s wobbly orbit cycles (called Milankovitch cycles). Not only was there a small rodent extinction every 2.5 million years, but a marked decrease in rodent population every million years or so.

In one instance, Spanish rodents were struggling to cling to life during a period 14 million years ago. At the same time, the Earth’s orbit was more circular than normal. That caused cooler temperatures on average – a challenging environment for rodents to survive in.