Aim: What were the first organisms to appear on Earth?

HW # 8 read chapter 19

Pg.493 q.#40 due thurs

Group work

Go through the progression of what we think happened to the earth

And

What formed in the oceanic soup

before life appeared

• Early Earth was hot; atmosphere contained poisonous gases

• Earth cooled and oceans condensed

• Simple organic molecules may have formed in the oceans

• Small sequences of RNA may have formed and replicated

• First prokaryotes may have formed when RNA or DNA was enclosed in microspheres

Once the organic compounds formed in the oceanic soup of the primitive atmosphere,

life was ready to form

Virus

BacteriaInfluenza virus

Bacterial cellProtozoan

Prokaryote Cells: (1st Major Kind of Cell)

Bacteria

lack a nucleus and don’t have membrane bound

organelles.

Virus Structure

Millions of years later the prokaryotes became photosynthetic and produced

oxygen

Gloeocapsa X 400

Anabaena X 400.

An oxygenated atmosphere capped by the ozonelayer protected the Earth

Aim: What are Eukaryotes?

Eukaryotic cells

Characteristics:

• Nucleus enclosed by a membrane

• Membrane covered organelles

Approximately 540 million years ago, at the beginning of the Cambrian Period, the fossil record at locations across Earth is marked by the dramatic appearance of complex, diverse, multicellular organisms with hard

parts.

Ocean Life Diversifies sponges, corals, and brachiopods occupied the seafloor, trilobites,

cephalopods

In Devonian time, from about 415 to 355 million years ago, fishes of many different types swam and hunted in the seas. Lobe-finned fishes — ancestors to the amphibians — and the early

sharks made their appearance by this time.

Amphibians • Some lobe-finned fish

evolved webbed, leg-like limbs. They probably lived in shallow swampy areas where their limbs allowed them to maneuver more easily than fins. Eventually, they evolved other support systems that prevented them from drying out and allowed them to move on land as the first amphibians. Although amphibians live on land, they must return to water to lay their eggs.

…and on land

• because seed-bearing plants do not need water to reproduce, they were able to spread into environments not open to the earliest plants. The casing keeps the seeds from drying out and protects the nutrients, allowing seeds to lie dormant through harsh conditions.

• Reptiles arose about 300 million years ago, and they replaced amphibians as the dominant land-dwelling animal following the Permian Extinction. Reptiles produce an egg that contains nutrients within a protective shell; unlike amphibians, they do not have to return to the water to reproduce. This difference allowed reptiles to move into new land environments.

First Dinosaurs

Approximately 230 million years ago, during the Triassic Period, the

dinosaurs appeared, evolved from the

reptiles

First Mammals

• Fossils of the earliest mammals are more than 200 million years old. These small, shrew-like animals probably lived in caves or burrows and hunted insects and small reptiles at night.

Age of Mammals

• The Cenozoic Era, from 65 million years ago to today, is the age of mammals and flowering plants and is marked by global cooling. The extinction of the dinosaurs allowed mammals to diversify and grow in size during the Cenozoic.

Human Ancestors

The first early hominids may have been

bipedal — walking upright on two legs

What does biodiversity mean?