LESSONS # 24

The Geological TimescaleThe Earth came into being about 4.6 billion years ago ( 4 600 000 000 years). This time is too long to think in terms of individuals years. So, scientists use something called the Geological Timescale.

The Geological Timescale divides the Earth’s History into broad eras, shorter periods and shorter still epochs.

Era

Period

Period

Epoch

Epoch

Epoch

Epoch

88% of Earth’s history was spent in the Precambrian Era

88%

4,600 Mya

Historic time 10,000 years

How the scientists have done the demarcations in the time scale?

For example, what is the distinction between the Permian period and the Triassic period?

Many of the transitions of the Geological Timescale are marked off for death of organisms on a grand scale in the form of “major extinction events”.

Cretaceous extinction (the most famous)

End of the dinosaurs, along with many other life forms. It was aided by the impact of one or more giant asteroids.

96% of the species of the Earth were wiped out.

Explosion on the diversity of animals.

Permian extinction (the greatest one)

Cambrian explosion

When did the transitions come about?

In Darwin's time there was no radiometric dating of materials. Therefore, each stratum and its fossils were assigned a relative date.

With scientific advances, specific dates have been assigned.

More than 2 billion years life consisted of nothing but microbes.

All the birds, reptiles, fish, plants, and mammals that exist today came about the last 16% of evolutionary time (last 600 million years).

Homo sapiens is an extreme latecomer.

First animals only 600 MyaLife began 3.8 billion years ago (3,800 Mya)

How did life begin?

Environment

Elements

Wherever life begun, life got going in WATER.

The environment where life got going had to have in it the chemical raw materials that could be used in forming life’s critical molecules: nucleic acids and proteins.

- Earth would have been a warm place (life may have originate in a warm little pond).

- Earth would have been frozen over in a global glaciation (life may have originate in a cold little pond).

Possible Sources of Earliest Life Elements

1- The gases Methane and Ammonia from Earth’s early volcanoes.

2- The building blocks (nucleotides and aminoacids) could have been arrived ready-made, delivered by meteorites and comets that smashed into the young Earth.

Meteorites, which landed on Australia in 1969, contained water and organic molecules such as aminoacids.

3- Organic raw materials came from the Methane and Hydrogen Sulphide from deep-sea vents on the floor of the oceans.

Materials pours forth from a hot water vent on the floor of the Atlantic Ocean. The fluid being emitted is mineral-rich enough to support bacteria and archaea that in turn form the basis for local food web.

Whatever the sequence of events, we move from simple molecules to the cellular ancestor of today’s organisms.

This cellular ancestor is called “universal ancestor”

The universal ancestor gave rise to all three domains: Bacteria, Achaea and Eukarya

The first kingdom with nucleated cells was the Protists.

All the organisms in the domain Eukarya have nucleated cells and are thus “eukaryotes”.

DomainBacteria

DomainArchaea

DomainBacteria

DomainArchaea

Domain Eukarya

Domain Eukarya(Protists, Plants, Animals, Fungi)

KingdomProtista

KingdomPlantae

KingdomAnimalia

KingdomFungi

gram-positive

purplebacteria

methaneproducers

floweringplants

evergreens

ferns

mossesdiatoms

dinoflagellates

flagellates

amoebae

mushrooms

vertebratesforam-inifera

saltlovers

hot acidlovers

Universalancestor

cyano-bacteria

inverte-brates

yeast

The first cell

Earth's Organisms and How They Evolved

Precambrian Era1- Precambrian Era is the first long period of the Geological Timescale.

2- Archaea and Bacteria got going (1).

3- Photosynthesis began in bacteria (for first time the sun’s energy is used to produce food).

4- Cyanobacteria were the first organisms to produce oxygen as a by product of photosynthesis.

6- First eukaryotic cells got going. (2)

5- Molecules of oxygen came together to form the gas Ozone, which rose through the atmosphere to form the ozone layer. For first time ever protection against UV radiation allows life to develop on land. (3)

8- 600 Mya, as the Precambrian Era was coming to close, the first fossil evidence of animal appears: multicelled organisms that get their nutrition from other organisms or organic material. (4)

7- Some bacteria invaded eukaryotic cells and, over time, the bacteria came to be integrated into the host cell, replicating along with them and given rise to the mitochondria.

Paleozoic Era

The Cambrian Explosion (5)

About 544 Mya started the Paleozoic Era. The first period of this era is the Cambrian Period.

It is the emergence of multitude of new animals forms, the like of which has never been seen before or since in evolution.

The fossil record indicates that, with one exception, every single one of the 36 phyla in the animal kingdom today came into being in the Cambrian explosion.

Cambrian Explosion took place in the seas. At the time, no life at all except for some hardy bacteria, existed on land.

Cambrian Explosion was followed for one major extinction event: The Cambrian Extinction (6) which demarked the transition to the Ordovician Period

Cambrian Explosion

Life in the Ancient Sea Floor

The Movement onto the Land: Plants First

When multicelled life came to the land, the first intrepid travelers were plant-fungi combinations, about 460 Mya. (7)

Some of the primitive plants were mosses that often hug the ground like green carpets.

Adaptations of Plants to the Land

1- Development of a vascular system (ferns)

2- Appearance of seeds (Gymnosperms), about 350 Mya (8)

3- Appearance of flowers (Angiosperms), about 165 Mya (9)

Bryophytes (mosses)

- No vascular structure

- They cannot grow up very far against gravity

- No seeds

Seedless vascular plants (ferns)

- Vascular structure

- They can grow up very far against gravity

- No seeds

Gymnosperms (conifers)

- Vascular structure

- They can grow up very far against gravity

- Seeds. Sperm can be carried by wind

Angiosperms (flowering plants)

- Vascular structure

- They can grow up very far against gravity

- Seeds. Sperm can be carried by wind

- Flowers

Vascular structure

Seeds

Vascular structure

SeedsFlowers

Vascular structure

Archaefructus sinensis, fossilized 125 million-years ago. The plant clearly had angiosperm-like trails.