The History of Life on Earth

AP Chapter 25

Figure 26.0 A painting of early Earth showing volcanic activity and photosynthetic prokaryotes in dense mats

Overview: Lost Worlds

• Past organisms were very different from those now alive

• The fossil record shows macroevolutionary changes over large time scales including– The emergence of terrestrial vertebrates – The origin of photosynthesis– Long-term impacts of mass extinctions

Fig. 25-1

Fig 25-UN1

Cryolophosaurus

The Age of the Earth

4.6 billion years

Figure 26.2 Clock analogy for some key events in evolutionary history

3.9 billion years ago

• Earth cooled, oceans formed, atmosphere contained nitrogen, CO2, methane CH4, ammonia NH3, and water vapor

• 1920’s Oparin and Haldane hypothesized that under those conditions, organic molecules could be formed

• 1953 Miller and Urey performed an experiment and produced organic molecules

Other ideas

• Submerged volcanoes, deep-sea vents

• Carbonaeceous chondrites found in meteorites contain C compounds

• Amino acid polymers from dripping organic monomers onto hot sand or clay

http://www.arizonaskiesmeteorites.com/AZ_Skies_Links/Chondrites_Main/Museum_Grade_Chondrites/Chondrite_1/index.html

All of these point to the possibility of an abiotic

synthesis of life.

• Life requires:

accurate replication and metabolism

• Protobionts – collections of abiotically produced organic molecules surrounded by a membrane

• Liposomes – evidence of this possibililty

Fig. 25-3

(a) Simple reproduction by liposomes (b) Simple metabolism

Phosphate

Maltose

Phosphatase

Maltose

Amylase

Starch

Glucose-phosphate

Glucose-phosphate

20 µm

First replicating molecule…

• RNA

• Why – capable of copying itself using ribozymes – enzyme-like RNA catalysts

• DNA would have replaced RNA as a better storage molecule

Figure 26.11 Abiotic replication of RNA

How is the age of fossils and rocks determined?

• Radiometric dating – using half-lives of radioactive isotopes

• Carbon-14 5,730 years

• Also patterns of magnetic reversal of the earth is used

• A fossil has 1/8th of the atmospheric ratio of C-14 to C-12. Estimate the age of the fossil.

3.5 billion yearsFirst Single-Celled Organism

• Oldest known fossils are stromatolites, rocklike layers of prokaryotes and sediment.

Figure 26.3 Early (left) and modern (right) prokaryotes

2.7 billion years agoOxygen

Evidence of oxygen accumulation from cyanobacteria in banded iron formations

2.1 billion years agoeukaryotic cells

• Fossils of eukaryotic cells

• Mitochondria and chloroplasts may have originated as prokaryotes engulfed by other prokaryotes in endosymbiosis.

• In serial endosymbiosis, mitochondria probably evolved first

1.5 billion years agoMulticellular organisms

• Oldest known fossils are algae

• Severe ice ages (Snowball Earth) prevented diversity of eukaryotes for awhile

535 – 525 Cambrian Explosion

• Great diversity of all types of eukaryotes

500 myaMovement onto Land

• Evolved adaptations to live on land and prevent dehydration

• Plants and fungi colonized land together

250 myaFormation of Pangaea

• Destroyed and altered habitats, changed climates, created geographic isolation

Mass Extinctions

• There have at least 5 mass extinctions.• Permian – 250 mya, over 90% of marine and

terrestrial species disappeared; maybe due to volcanoes, Pangeae, glaciation

• Cretaceous – 65 mya; ½ marine and many terrestrial forms, including dinosaurs; due to environmental changes or asteroids hitting the earth

• Mass extinctions provide many habitats and available niches to organisms that survive which leads to adaptive radiation.

• For ex, mammals did not change much until the after 65 mya and the extinction of the dinosaurs.

Evolution is not goal-oriented!

• Often very complex organs have evolved gradually from simpler structures, such as eyes.

• Evolutionary novelties may arise by modification of existing structures.