Fossil Atmospheres 

Growing Ancient Trees in Future Air

One of geology's biggest unanswered questions is: "How much does Carbon Dioxide (CO2) warm the Earth?" To answer this questions we want to trace how CO2 changed during past global warming events.  Problem: there is no fossil air from millions of years ago!  To estimate past CO2 levels we are measuring how leaves of "living fossi" Ginkgo change under high CO2.  We'll use similar changes in fossil Ginkgo leaves to estimate ancient CO2.

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We want to create a record of how the atmosphere has changed through time by calculating the ratio of two different types of leaf cell (stomatal and epidermal) for many leaves, from the present and the geological past. We know that the composition of the Earth's atmosphere has changed over time, and that it is changing now. It is important for us to understand what effect climate change might have on life on our planet in the long term.

One way we can understand the effect of climate change is to look at the geological past - millions of years ago - and the fossil record, to see what happened to organisms during periods of time in Earth history when there were similar changes in the atmosphere and climate. If we want to build an accurate picture of these past changes, we need to know what the atmosphere was like back then.

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Our planet's atmosphere is composed of many different gasses, one of which is CO2. Through extensive research we now know that CO2 concentration in the atmosphere has a very important influence on Earth's climate. There are several ways researchers try to reconstruct past climates; we call these climate proxies. One proxy for CO2 concentration comes from plants, and is known as stomatal index. This is a measure of the number of gas-exchange holes on the surface of a leaf, relative to the number of normal cells.