3.5 – Records of Past Climates Tree Rings, Fossils Coral Reefs, & Ice Cores

Who Studies Past Climates? paleoclimatologists = scientists who study past climates from thousands of years ago  These scientists use trees, fossils, sedimentary rock, coral reefs, and ice core samples to determine what life was like thousands of years ago pronounced: PALE – ee – o – klime – ah – tall – ah – jist

What do we call Evidence that Shows What Past Climates were Like? proxies = biotic (living) or abiotic (non-living) things that indicate what past climates were like  Common examples include tree rings, fossils, and ice core samples

Proxy #1: Tree Rings  Indicate what climate was like in the recent past –help indicate climate events like forest fires, floods, and drought

Tree Rings  Older (& larger) trees can show what climate was like up to a few hundred years ago  Some tree trunks from archaeological sites can tell what climate was like up to years ago!

 As a tree grows, it adds 2 layers (rings) of wood under its bark each year –the size & colour of the rings indicate what the temperature & rainfall were like that year  light ring = rapid growth (wet & cool conditions)  dark ring = slower growth (hot & dry conditions)

Learning Check  Look at the data from this tree ring. Which year do you think was the better growing season for the tree: or ? Why?  Can you tell what part of the year was better for growing?  What does that tell scientists about the climate that year?

Proxy #2: Ice Core Samples  Trees can’t help tell us what Earth’s climate was years ago  Sheets of ice that cover places like Antarctica, Greenland, and the Arctic have built up over millions of years  Like tree rings, layers of ice & snow accumulate year after year  The dust, ash, & gases trapped in the ice & snow tell us about what the atmosphere was like during the time that ice formed

Ice Core Samples  Scientists drill into the layers of ice & snow and pull out a tube of ice called an ice core –it tells them about the composition of the atmosphere when the ice formed

 Scientists drilling deep into ice and extracting cylinders of ice (ice cores)  Ice at the top is new  Ice at the bottom is thousands of years old

Ice Core Samples  The deeper scientists drill, the older the ice they access –scientists have drilled over 3 km deep into ice sheets, which yielded an ice core sample from over years ago!!

Evidence Gathered from Ice Cores 1. Types of particles trapped in ice –ex: dust, ashes, salts, pollen, gases –give clues about past events and conditions like volcanic eruptions, meteorite impacts, forest fires, plant life, etc.  concentrations of ash tells about forest fires or volcanoes that erupted  plant pollen tells about the plant life that lived there

2. What the air in the ice was made of –when water freezes, tiny air bubbles become trapped inside the ice –these pockets of air tell which greenhouse gases were present in the atmosphere when the ice formed

 Ice cores are cut into thin slices  Air bubbles within the ice are tested for gas e.g., CH 4, CO 2, SO 2, etc.  Gases within these bubbles show paleoclimatologists the different concentrations of gases throughout history More greenhouse gases = warmer periods Fewer greenhouse gases = colder periods

3. What the H 2 O was made of –Certain types of oxygen atoms are heavier than others  the more light oxygen there is trapped in these bubbles, the colder the air was when they formed  the more heavy oxygen, the warmer it was

 Preserved layers of dust in ice core samples help determine precipitation and volcanic activity

 Paleoclimatologists removing a sample of ice (from an ice core drill) from a glacier in Antarctica

The Warehouse

 Look carefully at the graphs that follow. Have CO 2 levels ever been as high as today’s levels?

 Why, then, are scientists warning of catastrophe in the future due to increasing CO 2 levels?  Because in the past, dramatic increases in CO 2 were a result of natural disasters like volcanic eruptions, meteorite strikes, etc., not a result of human activity

  Use the graph of CO 2 in the ice core sample on the left to guess the shape of the graph for temperature on the right t emperature (  C) year

Proxy #3: Coral Reefs  Coral are similar to trees  Like trees, coral grow layers every year  Layers of coral grow at different rates in warm water and cold water

Proxy #4: Fossils  Scientists use the remains or traces of ancient organisms (aka fossils) to learn what Earth’s climate was like when they were alive

Your turn!  Use p. 244 of your textbook and the Internet to explain how fossils can determine what past climates were like  Use Powerpoint to make a few slides (2 – 3) that describe how fossils are used to determine past climates –make your slides informative, colourful, and not too ‘wordy’ –add at least 3 pictures

Your turn! (Version 2)  Use your textbook on p. 244 and the Internet to explain how fossils can determine what past climates were like  Make a few slides (2 – 3 slides) that describe how fossils are used to determine past climates –make your slides informative & colourful –add at least 2 pictures