3.5 – Records of Past Climates3.5 – Records of Past Climates

Tree Rings, Fossils Tree Rings, Fossils

Coral Reefs, Coral Reefs,

& Ice Cores& Ice Cores

Who Studies Past Climates?Who Studies Past Climates?

paleoclimatologistspaleoclimatologists = scientists who = scientists who study past climates from thousands study past climates from thousands of years agoof years ago

These scientists use trees, fossils, These scientists use trees, fossils, sedimentary rock, coral reefs, and sedimentary rock, coral reefs, and ice core samples to determine what ice core samples to determine what life was like thousands of years agolife was like thousands of years ago

pronounced: pronounced: PALE – ee – o – klime – ah – tall – ah – jistPALE – ee – o – klime – ah – tall – ah – jist

What do we call Evidence that Shows What do we call Evidence that Shows What Past Climates were Like?What Past Climates were Like?

proxiesproxies = biotic (living) or abiotic = biotic (living) or abiotic (non-living) things that indicate what (non-living) things that indicate what past climates were likepast climates were like

Common examples include tree Common examples include tree rings, fossils, and ice core samplesrings, fossils, and ice core samples

Proxy #1: Tree RingsProxy #1: Tree Rings

Indicate what climate was like in the Indicate what climate was like in the recent pastrecent past– help indicate climate events like forest help indicate climate events like forest

fires, floods, and droughtfires, floods, and drought

Tree RingsTree Rings

Older (& larger) trees Older (& larger) trees can show what can show what climate was like up to climate was like up to a few hundred years a few hundred years agoago

Some tree trunks Some tree trunks from archaeological from archaeological sites can tell what sites can tell what climate was like up to climate was like up to 10 000 years ago!10 000 years ago!

As a tree grows, it adds 2 As a tree grows, it adds 2 layers layers (rings) of wood (rings) of wood under its under its bark each yearbark each year– the size & colour of the rings indicate the size & colour of the rings indicate

what the temperature & rainfall were like what the temperature & rainfall were like that yearthat year light ring = rapid growth light ring = rapid growth (wet & cool conditions)(wet & cool conditions)dark ring = slower growth dark ring = slower growth (hot & dry conditions)(hot & dry conditions)

Learning CheckLearning Check

Look at the data from Look at the data from this tree ring. Which this tree ring. Which year do you think was year do you think was the better growing the better growing season for the tree: season for the tree: 2002-2003 or 2004-2002-2003 or 2004-2005? Why? 2005? Why?

Can you tell what part Can you tell what part of the year was better of the year was better for growing? for growing?

What does that tell What does that tell scientists about the scientists about the climate that year?climate that year?

Proxy #2: Ice Core SamplesProxy #2: Ice Core Samples

Trees can’t help tell us what Earth’s Trees can’t help tell us what Earth’s climate was 100 000 years agoclimate was 100 000 years ago

Sheets of ice that cover places like Sheets of ice that cover places like Antarctica, Greenland, and the Arctic have Antarctica, Greenland, and the Arctic have built up over millions of yearsbuilt up over millions of years

Like tree rings, layers of ice & snow Like tree rings, layers of ice & snow accumulate year after yearaccumulate year after year

The dust, ash, & gases trapped in the ice The dust, ash, & gases trapped in the ice & snow tell us about what the atmosphere & snow tell us about what the atmosphere was like during the time that ice formedwas like during the time that ice formed

Ice Core SamplesIce Core Samples

Scientists drill into the Scientists drill into the layers of ice & snow layers of ice & snow and pull out a tube of and pull out a tube of ice called an ice called an ice coreice core – it tells them about the it tells them about the

composition of the composition of the atmosphere when the atmosphere when the ice formedice formed

Scientists Scientists drilling deep drilling deep into ice and into ice and extracting extracting cylinders of ice cylinders of ice (ice cores)(ice cores)

Ice at the top is Ice at the top is newnew

Ice at the Ice at the bottom is bottom is thousands of thousands of years oldyears old

Ice Core SamplesIce Core Samples

The deeper The deeper scientists drill, the scientists drill, the older the ice they older the ice they accessaccess– scientists have scientists have

drilled over 3 km drilled over 3 km deep into ice sheets, deep into ice sheets, which yielded an ice which yielded an ice core sample from core sample from over 800 000 years over 800 000 years ago!!ago!!

Evidence Gathered from Ice CoresEvidence Gathered from Ice Cores

1.1. Types of particles trapped in ice Types of particles trapped in ice– ex: dust, ashes, salts, pollen, gases ex: dust, ashes, salts, pollen, gases – give clues about past events and give clues about past events and

conditions like volcanic eruptions, conditions like volcanic eruptions, meteorite impacts, forest fires, plant meteorite impacts, forest fires, plant life, etc.life, etc.

concentrations of ash tells concentrations of ash tells about about forest fires or forest fires or volcanoes volcanoes that eruptedthat erupted

plant pollen tells about plant pollen tells about the the plant life that lived thereplant life that lived there

2.2. What the air What the air in the ice was made ofin the ice was made of– when water freezes, tiny air bubbles when water freezes, tiny air bubbles

become trapped inside the icebecome trapped inside the ice– these pockets of air these pockets of air tell tell

which greenhouse which greenhouse gases were gases were present present in the in the atmosphere atmosphere when the when the ice formedice formed

Ice cores are cut into thin slicesIce cores are cut into thin slices Air bubbles within the ice are tested for gas Air bubbles within the ice are tested for gas

e.g., CHe.g., CH44, CO, CO22, SO, SO22, etc., etc. Gases within these bubbles show Gases within these bubbles show

paleoclimatologists the different concentrations paleoclimatologists the different concentrations of gases throughout historyof gases throughout history

More greenhouse gases = warmer periods

Fewer greenhouse gases =

colder periods

3.3. What the H What the H22O was made ofO was made of– Certain types of oxygen atoms are heavier Certain types of oxygen atoms are heavier

than othersthan others the more light oxygen there is the more light oxygen there is

trapped in these bubbles, the trapped in these bubbles, the colder the air was when they colder the air was when they formed formed

the more heavy oxygen, the the more heavy oxygen, the warmer it warmer it waswas

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

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

The WarehouseThe Warehouse

Look carefully at the graphs that Look carefully at the graphs that follow. Have COfollow. Have CO22 levels ever been as levels ever been as high as today’s levels?high as today’s levels?

Why, then, are scientists warning of Why, then, are scientists warning of catastrophe in the future due to catastrophe in the future due to increasing COincreasing CO22 levels? levels?

Because in the past, dramatic Because in the past, dramatic increases in COincreases in CO22 were a result of were a result of natural disasters like volcanic natural disasters like volcanic eruptions, meteorite strikes, etc., not eruptions, meteorite strikes, etc., not a result of human activitya result of human activity

Use the graph of CO2 in the ice core sample on the left to guess the shape of the graph for temperature on the right

tem

pera

ture

(C

)year

Proxy #3: Coral ReefsProxy #3: Coral Reefs Coral are similar Coral are similar

to treesto trees Like trees, coral Like trees, coral

grow layers grow layers every yearevery year

Layers of coral Layers of coral grow at different grow at different

rates in warm rates in warm water and cold water and cold

waterwater

Proxy #4: FossilsProxy #4: Fossils Scientists use the remains or traces Scientists use the remains or traces

of ancient organisms (aka of ancient organisms (aka fossilsfossils) to ) to learn what Earth’s climate was like learn what Earth’s climate was like when they were alivewhen they were alive

Your turn!Your turn!

Use p. 244 of your textbook and the Use p. 244 of your textbook and the Internet to explain how fossils can Internet to explain how fossils can determine what past climates were determine what past climates were likelike

Use Use PowerpointPowerpoint to make a few slides to make a few slides (2 – 3) that describe how fossils are (2 – 3) that describe how fossils are used to determine past climatesused to determine past climates– make your slides informative, colourful, make your slides informative, colourful,

and not too ‘wordy’and not too ‘wordy’– add at least 3 picturesadd at least 3 pictures

Your turn! (Version 2)Your turn! (Version 2)

Use your textbook on p. 244 and the Use your textbook on p. 244 and the Internet to explain how fossils can Internet to explain how fossils can determine what past climates were determine what past climates were likelike

Make a few slides (2 – 3 slides) that Make a few slides (2 – 3 slides) that describe how fossils are used to describe how fossils are used to determine past climatesdetermine past climates– make your slides informative & colourfulmake your slides informative & colourful– add at least 2 picturesadd at least 2 pictures