Whenever an airplane crashes, you hear about investigators retrieving the plane's black box. It's a device that records essential information about the plane's operation, and it can help investigators reconstruct what happened to bring the plane down.
|Tree rings show a tree's history. Claire Eamer photo|
One of the best known black boxes is tree rings. Each year, a tree puts on a ring of new growth. In a good year, the growth ring will be wider, in a bad year, narrower. The science of studying what tree rings can tell us is called dendrochronology, and it has provided a huge amount of information about both natural and human history.
Trees aren't the only organisms that save information in rings. So do fish -- but their growth rings are in their ears. Tiny, disc-shaped bones in fishes' ears -- called otoliths or ear stones[PDF] -- add a ring of growth for every year of a fish's life. As with tree rings, the otolith rings vary, depending on the conditions the fish encountered that year. Even the chemistry of the annual rings changes, so they can hold information about the water the fish traveled through.
|The annuli are visible as ridges on this ram's horns.|
The biggest natural black box of all is Earth's ice. The great icefields in places like Greenland and Antarctica have been frozen for hundreds of thousands of years -- or even longer. But that ice didn't arrive all at once. It built up year by year with layers of snow that fell and then were compressed into ice by the layers that followed. Digging straight down into a massive icefield is like digging into the past.
|Greenland glaciers like this one contain ice more than 100,000 years old.|
And that's what icefield scientists do. They drill into glaciers and icefields and extract long cores of ice. Then they analyze the thin layers, examining the chemistry of the water and bubbles of trapped air, the dust and pollen that settled on the glacier's surface, and anything else that might be frozen in the ice. The oldest ice found so far came from Antarctica and is an amazing 2.7 million years old. Ice cores are among the most powerful climate proxies we have, and much of our knowledge of very ancient climates comes from them.
For more information about dendrochronology, explore the EnvironmentalScience.org website.
For some of the things we can learn from fish otoliths, watch the short video on this page.
For a detailed explanation of ice core science, browse through Ice Core Basics.
And for more on climate proxies, try this NOAA site or this page on Palaeoclimatology.