Overview

Geologic events that alter environments change the course of biological evolution Example: Large lake splitting into several

small lakes

Living things change the planet they inhabit Example: Evolution of photosynthetic

organisms putting oxygen into the atmosphere

Photosynthetic Cyanobacteria

26.1

Cells produced in 4 stages 1. Abiotic synthesis of AA & nucleotides

(organic compounds) 2. Joining of monomers into polymers 3. Packaging into protobionts – droplets

with membranes that maintained an internal chemistry different from the environment.

4. Origin of replication that made inheritance possible

Evidence for each of these 4 stages discussed

1. Synthesis of organic compounds

Earth formed about 4.6 billion years ago

Conditions on early Earth were very different from today

“Primitive soup” experiment of Miller and Urey Strongly reducing atmosphere

Hydrogen Methane Ammonia Water vapor Sparks to mimic lightning

Conception of Earth 3 billion years ago

Extraterrestrial Sources of Organic Compounds Amino acids that reached early Earth

aboard chondrites could have added to the primitive soup

Looking to other planets for signs of life Present day Mars = no life Billions of years ago it was warm, liquid

water, and carbon dioxide in the atmosphere

2. Abiotic synthesis of polymers

Researchers have produced amino acids polymers by dripping solutions of amino acid monomers onto hot sand, clay, or rock

Formed spontaneously

3. Protobionts

Replication and metabolism are essential for life

Protobionts: aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure.

Exhibit some properties of life and could have formed from abiotically produced organic compounds

4. Origin of replication

The first genetic material was probably RNA

Had the ability to copy itself and began to appear in protobionts

RNA could have been the template on which DNA was assembled DNA is much more stable and can be replicated

more accurately so as genomes grew DNA grew

RNA world gave way to a DNA world and RNA took over its role that we see it in today

26.2 The fossil record

Fossils are found in sedimentary rocks

Index fossils: the strata at one location can often be correlated with strata at another location by the presence of similar fossils known as index fossils

Radiometric dating

Radiometric dating: decay of radioactive isotopes

Half-life: the number or years it takes for 50% of the original sample to decay

Carbon-14 has a half life of 5,730 years so it is useful for dating fossils up to about 75,000 years old

Potassium-40 used to date much older fossils (530 million years old)

Magnetism of rocks can also provide dating information

Geologic record 3 Eons

Archaean & Proterozoic lasted approx. 4 billion years

These are known as Precambrian Phanerozoic eon –the last half billion years is most of

the time multicellular eukaryotic life has existed Divided into 3 eras

Paleozoic Mesozoic Cenozoic

Boundaries between eras correspond to times of mass extinctions seen clearly in the fossil record

Mass Extinctions

2 mass extinctions have received the most attention Permian & Cretaceous

Permian – at the boundary between Paleozoic and Mesozoic eras claimed about 96% of marine animal speices

Cretaceous – at the boundary between Mesozoic and Cenozoic eras doomed more than half of all marine species and many families of terrestrial plants and animals including the dinosaurs.

Permian mass extinction caused by volcanic eruptions that increased the carbon dioxide and warmed the global climate

Cretaceous mass extinction caused by an asteroid or comet hitting the earth that spewed up dust and blocked sunlight for several months.

Impact Crater

26.3

Oldest known fossils Date to 3.5 billion

years ago Stromatolites Composed of layers of

bacteria and sediment

Found today in a few warm, shallow, salty bays

Prokaryotes

Prokaryotes were Earth’s sole inhabitants

3.5 to about 2 billion years ago

The oxygen revolution

Earliest types of photosynthesis did not produce oxygen

Oxygenic photosynthesis evolved 3.5 billion years ago in cyanobacteria

When oxygen started to accumulate in atmosphere It posed a challenge for life It provided an opportunity to gain abundant

energy from light It provided organisms an opportunity to exploit

new ecosystems

26.4 – Eukaryotes Oldest fossil eukaryotes

date back 2.1 billion years

Arose from Endosymbiosis and genetic exchanges between prokaryotes Endosymbiotic theory

states that chloroplasts & mitochondria were formerly prokaryotic organisms living within larger cells.

Endosymbiosis Mitochondria and plastids were formerly

small prokaryotes living within larger host cells

Gained entry to the host cell as undigested prey or internal parasites

The host and endosymbionts would have become a single organism

Evidence to support theory: Similarities in inner membrane structures

and functions Both have their own circular DNA

26.5 - Multicellularity

Evolved several times in eukaryotes

Oldest fossils of eukaryotes, small algae that lived 1.2 billion years ago

1st multicellular organisms were colonies

Cambrian Explosion

Most of the major phyla of animals appear here

Colonization of land by plants, fungi,

and animals Occurred about 500 million years ago

Adaptations that helped prevent dehydration made it possible to move out of water onto land

Symbiotic relationships between plants and fungi began at this time and exist today

Continental Drift

Continents are not fixed but drift across our planet’s surface on plates of crust that float on a hot underlying mantle

Interactions at plate boundaries Convergent boundaries (moving together) Divergent boundaries (moving apart) Transform boundaries (sliding past one

another)

Volcanoes, Earthquakes, mountain building, and subduction occur at plate boundaries

The formation and breakup of the supercontinent Pangaea explain many biogeographical puzzles Land bridges Fossils found on 2 continents that

can’t swim Rock formations Apparent puzzle piece fit of the

continents

26.6 Taxonomic systems

Old system was 2 Kingdoms (Plant & Animal)

5 kingdom system Monera, Protists, Plantae, Fungi,

Animalia

3 Domain system has replaced the 5 kingdom system Archaea, Bacteria, Eukarya