SNC 2D
9.1 Discovering Past Climates
Discovering Past Climates
People have been recording weather __________ for only a few hundred years. To learn about what Earth’s
________________ was like a few centuries ago, scientists must get creative.
People who study past climates are called ___________________________.
What Tree Rings Reveal About Past Climates
Tree_______________ is affected by _________________________ and ____________________________. The
amount that a tree grows each season is indicated by the size and colour of the ________________
_________________. ____________________________________ study details about the size, colour, and shape of
each ring.
A wide tree ring indicates wet and cool weather, which allows trees to grow ______________. A thin ring is produced in
dry and ________ conditions, when tree growth is ________________. A dark ring marks growth during late summer,
and a light-__________________ ring indicates growth during spring.
Living trees hold records of climate dating back no more than a few hundred _________________. Tree trunks from
archaeological sites allow scientists to determine what climate was like a few thousand years ago.
Ice Cores-Records of Past Climates
Like tree rings__________________ of snow and ice accumulate year after year. To uncover evidence of past climate
____________________, scientists use a special drill, that _______________________ deep into the layers to extract
long, cylinder-shaped samples called ice _______________. Scientists study the __________________________ and
_____________________________ of the ice in each layer in order to make inferences about past climates.
Evidence of Past Climates Obtained from Ice Cores
Ice cores hold four types of clues __________________ in time:
1. Dissolved and _____________________ matter in ice – (dust ashes, salts, plant ________________, and other
material) Frozen samples of these materials give clues about events and conditions, such as volcanic
_________________________, meteorite impacts, forest _________________, and vegetation cover.
2. __________________ characteristics of the ice - (crystal size and shape) indicate the conditions of
_____________________ and _________________ at the time the ice crystals formed.
3. The composition of trapped ___________ bubbles - When water _______________, tiny air bubbles in the
water may become ____________________ inside the ice. These pockets of air allow scientists to analyze the
concentration of greenhouse ________________ over hundreds of thousands of years.
4.
The composition of the ice - Water (H2O) contains varying ______________ of hydrogen and oxygen isotopes.
__________________ are different forms of an atom. Water that contains oxygen-18 _________________ at a
higher _____________________ than water that contains oxygen-16. In addition, water that contains oxygen16 evaporates more quickly than water that contains oxygen-18.
Therefore, the relative _______________________ of isotopes in different layers of ice indicates the
temperature at the _____________________ the ice formed.
Evidence of Past Climates from Sedimentary Rock
To obtain evidence of climates older than can be _________________________ in ice cores, scientists examine
__________________. Every year, billions of tons of ___________________ (fragments of rock) wash from the land and
accumulate in thick ____________________ on ocean floors and lake beds.
The hard parts of small sea ____________________ (such as diatoms and alge) and _____________________ from
flowering plants are ________________ in these sediments.
Over long periods of time, this ______________________ material becomes compressed and _____________________
into sedimentary rock.
What Sediment Cores from Lakes and Oceans Reveal
Data from the study of sediment cores gives insight into:
o
o
o
___________________________________________ during a specific time (by knowing the common living
thing)
The ____________________________________________________________ in which an organism lived
The _____________________________________________________________________________________
__________________________________ (by analyzing the composition and amount of sediment in layers)
Evidence of Past Climates from Fossils and Preserved Organisms
The remains or traces of living things, called __________________, also provide valuable clues when paleoclimatologists
reconstruct past climates.
The types and abundance of fossilized _______________________ in each rock layer help scientists reconstruct the
___________________________ at the time the layer formed – including the _________________. Because plants and
animals are uniquely _________________________ to the environment in which they live, studying these fossils gives
scientists clues about what environments were like _______________________ of millions of years ago.
The Rate of Climate Change
Scientists are still ______________________ whether climate change is affected more by slow, ___________________
changes or by sudden, ___________________________ changes. This question is at the centre of the
__________________________________ about whether humans can cause earth’s climate to change significantly.
However, most __________________________ agree that humans are affecting the composition of the Earth’s
__________________________. This influence may ____________________ or ______________________ the rate at
which __________________________________ progresses.