Transcript 2-fossils and rock dating

Fossils: are the remains of animals, plants or
humans found in sediments and rocks.
e.g. bones, shell, leaves, carapace.
Fossilization: transformation of a living organism
into a fossil. This is a very long
process.
• The process of fossilization:
– The animal, plant or human dies
– Soft tissues (muscles and organs) are eaten
or decomposed
– The hard parts (skeleton) are covered with
sediment
– Over years, the sediments harden into rocks.
– The fossils are found by scientists…or you!
• Fossilization of a dinosaur:
• What do fossils teach us?
– A) the different forms of life that have existed
on Earth.
– B) the changes that have marked Earth’s
history
• Tectonic plates have changed Earth’s appearance
and that is why similar fossils are found on
different continents far away from each other.
• Stratigraphy: sediments deposited on
ocean floor, form rocks over time and are
usually arranged in layers.
• Every stratigraphic layer is composed of
sedimentary deposits of the same color,
size and type of rock.
• The oldest layer is always on the bottom
with the youngest layer on the very top.
This is the principle of superposition.
– E.g. old vs. new newspaper in the recycling
bin.
• Dating fossils:
– There are two methods of dating fossils
• Relative dating: determining the age of fossils and
rocks by examining their location in the
superpositioned layers.
• Absolute dating: determining the age of fossils
and rocks by measuring the quantity of certain
radioactive elements (uranium and carbon 14) in
the specimen.
• Index fossils: are fossils that help
scientists find the approximate age of
layered sediments.
• E.g. Scientists know the age of ammonites, a
marine animal. When ammonites are found in rock
layers, scientists know that the rock is
approximately 110 Ma because that is the age of
the ammonite found within.