Section 4 science, earth

paleontologists

study early life forms by interpreting fossil evidence

fossils

traces of once living things that are preserved in rocks

formations of fossils by mold and cast

1. remains sink in water and are quickly buried by sediment. Soft parts decay

2. over millions of years, the sediment turns to rock, the hard parts dissolve forming a mold

3. other sediments or minerals fill the mold, creating a cast of the remains

carbonaceous film

the remains of an organism were compressed under heat and pressure, leaving a thin carbon film

original remains

preserved in ice, tar or amber

trace fossils

evidence of animal activity, such as worm holes, burrows and footprints

petrified fossils

minerals permeated the remains, causing them to harden

geological column

in a geological, older layers of sedimentary rock are at the bottom and younger layers are on top.

can use layers to help determine the ages of fossils and the environment they formed

index fossils

can be used to identify a particular time period

uncertainties in fossil records

fossils are rare (need certain conditions to form)

fossils dont tell us everything

often, fossils are found in fragments that have to be reconstructed

earths first years

• the earth is 4.6 billion years old

• earth started as a swirling cloud of gas and dust around the sun

• gas and dust collected together, forming planets

• over time, the outer layers of earth cooled. eruptions of magma from underneath cooled to form an outer layer ok rock

Precambrian era

• 4.6b to 600m years ago

• earth forms

• first life (bacteria)

• first invertebrates

paleozoic era

• 600 to 225m years ago

• first reptiles

• first large land animals (amphibians)

• first insects

• first large land plants

• first fish with jaws

mesozoic era

• 225 to 65m years ago

• dinosaurs

• first flowering plants

• first birds and mammals

cenozoic era

• 65m years ago to present

• most modern species appear

• more mammals

• first grasses

• first human like species