How do we know what our climate was like thousands of

years ago?

Ice Cores

• Scientists collect a cylindrical section of ice from a glacier or an ice sheet

• Chemical analyses are performed on air trapped in the ice

• scientists can estimate the percentage of carbon dioxide and other trace gases in the atmosphere at a given time.

Changes in Carbon dioxide in the Atmosphere from 1700 to 2000

Tree rings Plant Fossils

Pollen record

• Pollen grains can accumulate in sediment.

• Different types of pollen in sediment reflect the vegetation of that time

• From the vegetation we can determine the climate

The Paleoclimate of Blackhawk, Colorado

Peat Bog

• In a valley on a farm a peat bog developed

• The peat bog and soils underneath it have been in existence for eons and collected sediments over time

Pollen Grains

• Trapped in these sediments are several different varieties of pollen grains

• By looking at these sediments we can reconstruct the vegetation in the farm’s area during the last several thousand years

Your Assignment

• Based on pollen data collected from a peat bog in Colorado

• You will analyze sediment samples with other material mixed in to represent pollen grains

• Using the key you will determine the type and amount of “pollen” in the samples

Your Assignment

• From this information you will determine:– The type of vegetation– Age of the samples AND– Present conclusions about the likely climate at

the time the pollen was shed

You will:• Work in pairs• Be given a sediment sample, tweezers, and pie pan• Sift and dig until you have found ALL of the pollen in your

sediment sample• Separate the pollen grains by color or shape• Use the pollen key to determine what species of plants are

represented from each sample and calculate what percentage comes from each species for the sediment layer you are working on

• Record this information on your data sheet• Use this information to decide what the climate was like when

your layer was deposited• Compare your sample to those from other layers of the

sediment core• Complete work sheet and one paragraph description of the

climate for your core

Final assessment

• Visit with the paleoclimatologists who studied each of the six sediment layers.

• Compare results.

• Use the class data to construct a timeline representing the last 8,000 years. On your timeline indicate what species were most common and a brief summary of the climate during that period.