Download Interpreting Geological Change

Interpreting Geological
Change
Section 4.1 p. 411-414
Section 4.2 p. 415-418
Section 4.3 p. 419-424
Learning Outcomes
• Describe the nature of different kinds of fossils, and identify
hypotheses about their formation
• Explain and apply methods used to interpret fossils
• Identify uncertainties in interpreting individual items of fossil
evidence; and explain the role of accumulated evidence in
developing accepted scientific ideas, theories and
explanations
What is a Fossil
• Fossils are preserved impressions in rock that tell us when, where, and how living
organisms lived and behaved millions of years ago
• The word fossil means ‘dug out of the ground’.
• The majority of fossils are found in exposed sedimentary rock.
• The most common types of fossil rocks are limestone, sandstone and shale.
• Paleontologists are scientists who study early life forms by interpreting plant and
animal fossils
• Most fossils are fragments or parts of skeletons, shells or other animal traces.
• The inferences made suggest that life on Earth has changed a great deal over the past
million of years
Trilobite
• Fossils found in younger rocks are much like the organisms living today.
• Older rocks contain fossils of organisms that are extinct (no longer existing)
300
million
years ago
Formation of a Fossil
• 4 Step Process
• When the organism dies it remains on the
ground
• Sediment gradually covers it
• Eventually the seiment with the organism
inside it hardened into rock
• When you crack open the rock, you will find
the impression of the organisms skeleton
• Remains of dead plants and animals that have been
protected from scavengers can become fossilized in a
number of ways:
• petrified (rock-like) fossils preserve the bones of dead animals by
using silica
• an outline or impression from the carbon residue on rock surfaces
can provide a carbonaceous film
• original remains may be preserved in tar, amber or peat bogs
• trace fossils are evidence of animal activity, like worm holes,
footprints, and burrows
Telling Time Geologically
• The layers of sediment have formed over millions of years are
called Strata
• From studying the kind of rock and grain size in a layer of strata,
geologists can gather information about the environment in which it
formed
• If found in limestone this layer of rock was originally at the bottom of the ocean
• If the layer of strata is very think, the environment was stable for quite some
time
• A new layer is formed when something major changes in the
environment
• Rise in seawater would create a change in the type of sediments (would now be
replaced by sediments found in deeper water
• Where a fossil is found in a strata tells a paleontologist when that
creature existed
• Strata forms geological columns that let scientists know the approximate
age of the fossilized organism
• Youngest organisms closer to the surface
• Oldest organisms closer deeper towards the bottom
• This is what allows scientists to see the evolution of creatures over time
Studying Sedimentary Layers
• In areas where the layers of sedimentary
rock are deeply eroded, geologists can study
the fossil record over a large portion of
Earths History
• Grand Canyon
• Red Deer River (Central Alberta)
• The Royal Tyrrell Museum
•
•
•
•
Opened in 1985,
Named after Joseph Burr Tyrrell,
Located in the Bad Lands of Alberta (Drumheller)
1884 while studying coal deposits, discovered 70
million year old dinosaur skull (Albertosaurus)
• Sparked interest (turned out to be one of the
worlds richest deposits of Dinosaur bones)
• Museum now displays over 200 dinosaur
remains
Geological Time
• Geologists have used the knowledge found from fossils to organize
Earths history into geological time intervals
• These time periods are called Era’s
• An Era is based on a sequence of rock strata (oldest on bottom, newest up
top)
• Often named after areas where rocks from that period were exposed
• Jurassic is named after Jura, a mountain range in France
• Four Main Divisions of these sequences
• Precambrian Era (4600 to 600 Million Year ago)
• Formation of Earth
• Fist simple organisms (bacteria)
• First soft-body animals (no vertebrae)
• Paleozoic Era (600 to 225 million years ago)
•
•
•
•
•
First Reptiles
First large land animals (amphibians-Frogs)
First Insects
First Large land plants
First fish with Jaws
• Mesozoic Era (225-65 Million Years Ago)
• Dinosaurs rule and become extinct
• First flowering plants
• First birds and animals
• Cenozoic Era (65 million years ago to today
•
•
•
•
Appearance of most modern day species
Many more species of mammals
First grasses
First human like species (about 2-3 million years ago)
Understanding Fossil Evidence
• Fossils are very rare
• It can be very hard to come up with enough concrete evidence to make general
statements about how life occurred back then
• Some fossils of Archaeopteryx have been discovered with feather like impressions, but too
few to have been found to make a statement saying that all similar creatures at the time
had feathers
• Putting together a fossil is like putting together a puzzle with no picture, and
potentially missing pieces
• Very difficult
• Requires knowledge of anatomy, and Imagination