Evolution and Fossils

Fossils:

• Fossil: the preserved or mineralized remain or imprint of an organism that lived long ago.

Age of rocks can tell us the age of fossils

Fossils are remains of ancient life

3 major points on evolution through the

use of the fossil record:•Earth is about 4.5 billion years old

•Organisms have inhabited Earth for most of its history

•All organisms living today evolved from earlier, simpler life forms

• Most fossils form when organisms and traces of organism are rapidly buried in fine sediments deposited by water, wind or volcanic eruptions

• Paleontologists: scientists who studies fossils.

Becoming A Fossil• Scientists have

described about 250,000 different fossil species– Yet that is a small fraction of

those that lived in the past!

• Evolution can be seen in the fossil record.– Fossilized species found in

older rocks are different from those found in newer rocks

•

Fossil formation• The oldest fossils are

remains of marine organisms that populated the planet's oceans.

• When they died, the plants and animals were buried by mud, sand, or silt on the sea floor.

• Land animals and plants usually decomposed or were eaten, and mainly the hard parts -- teeth, bones, shells, or wood -- were preserved.

Fossils can be formed in several ways

• Buried bone and shell contain tiny air spaces into which water can seep, depositing minerals.

• Reinforced by these mineral deposits, bone and shell can survive for millions of years.

• Even if the bone or shell dissolves, the mineral deposits in the shape of the body structure remain.

Quick Recap:

• Arrange fossils in sequence from oldest to youngest to see patterns of evolution

• Fossils are classified according to the way they are found

Fossils are found in layers of rock

• The oldest rock layers (and therefore the oldest fossils) are always on the bottom

• The youngest are on top.

• This is referred to as superposition (super = above)

Oldest to the bottom:

Becoming a Fossil

http://www.ucmp.berkeley.edu/education/explorations/tours/fossil/9to12/intro.html

Organisms die and are buried by sediment

• Their weight causes the lower layers to harden into sedimentary rock, trapping the organism or trace inside.

Not all fossils are formed by sediment

Found in Tar Pit

Found in Amber

• http://www.pbs.org/wgbh/evolution/library/04/3/l_043_01.html

• Casts: a mold of an organism is created and then filled by minerals making an exact copy

• Molds: AN organism decays leaving an empty space in the rock that is the exact shape of the organism

• Imprints: Thin objects such as leaves or feathers fall into mud and then mud hardens

• Trace Fossils: Evidence of animal activity (footprints, trails, etc.)

• Petrified fossils: the hard part of the organism is replaced with minerals and the minerals harden making an exact stone copy.

• Amber-preserved: Rare, but when found whole organism is preserved.

• Interpretation of fossils poses another set of challenges

• Their age can only be estimated by radiometric dating of rocks they were found near or within

Relative dating:

•fossils on the bottom are the oldest, and the ones on the top are the youngest

– Only tells if one fossil is older than another

Relative dating:

•fossils on the bottom are the oldest, and the ones on the top are the youngest

– Only tells if one fossil is older than another

Radiometeric dating:

•radioactive isotopes are used to determine age of fossil

Radiometeric dating:

•radioactive isotopes are used to determine age of fossil

Fossils can show us how ecosystems change• Nevada’s Silver Peak Mountain Range

Fossil of a marine animal found in the rocks of the desert

• Archaeocyathids were a group of sponges that lived about 500 million years ago, and are now extinct.

• They built huge reefs (similar to coral reefs we see today) and were extremely important members of their ecosystems

What could explain finding fossils of sponges in the Nevada desert?