History of Life Section 14.1

Reminder: Don’t forget to bring your 100 pennies per pair.

Early History of Earth What was it like? Scientists suggest that it was… Very hot Atmosphere contained little Oxygen. Had a lot of water vapor, carbon dioxide and nitrogen.

Evidence suggests that the earth is 4.6 billion years old. However, it is possible that life originated between 3.9 and 3.5 billion years ago.

Do Scientists Know for Sure? Why Not?

What do Scientists Use to Study the history of earth? Oldest rocks on the earth formed 3.9 billion years ago. Importance Source of Information about the diversity that existed on the planet.

Scientists can’t just look at the organisms alive today to learn about biodiversity. About 99% of species that have ever lived are extinct.

Fossils Provide Clues to the Past A fossil is evidence of an organism that lived long ago.

Types of Fossils Trace fossils Casts Petrified Fossils Imprints Amber-preserved and frozen fossils Molds

Trace fossils A trace fossil is the marking left by an animal and may include a footprint, a trail, and a burrow.

Casts When minerals in rocks fill a space left by a decayed organism, they make a replica, or cast, of the organism. Mesosaurus

Petrified Fossils Minerals sometimes penetrate and replace the hard parts of an organism, producing copies of them.

Imprints A thin object, such as a leaf, that falls into sediment can leave an imprint when the sediment hardens into rock.

Molds A mold forms when an organism is buried in the sediment and then decays, leaving an empty space. Trilobite

Amber-Preserved and Frozen At times, an entire organism was quickly trapped in ice or tree sap that hardened into amber.

What is the limitation of fossils? Fossils are only snapshots of history. The information is limited.

For example, what can you tell from this picture?

Paleontologists Paleontologists-scientists who study ancient life. Like detectives of the past.

Suppose…. ...paleontologists were to uncover rocks that had a layer with fossilized ferns and then the layer above it had the fossilized remains of fish? What would they be able to deduce?

Paleontologists use different clues to discover things about the organisms and climate of the area Clues like condition, position, and location of rocks and fossils.

Fossils are usually found in sedimentary rock Fossils are usually found in sedimentary rock. This is because of the differences in how rocks are formed.

How fossils are formed An organism dies.

How fossils are formed. The remains are covered by sediment.

How Fossils are Formed. Hard parts get replaced by minerals in the soil and form into rock by compression.

How Fossils are Formed. Earth Movements or erosion may expose the fossil millions of years later.

How do we determine the age of a fossil? Two methods: Relative Dating Radiometric Dating

Relative Dating Dating the past by how it was laid down. Oldest is generally on the bottom. Can determine order of species.

Radiometric Dating Use to determine the actual age of an organism. Radioactive isotopes decay at a specific rate. Knowing this rate, scientists are able to discover the approximate age of a certain rock or fossil.