History of Life



History of Life

Measuring the Past

Humans and all other organisms are part of the natural world

Natural processes shape the Earth and the living things that reside on the Earth

All living things are the products of evolution

Measuring the Past

Humans share features with other animals due to shared evolutionary ancestry

e.g., Our genetic code is identical to that of virtually every living organism

Same relationship between codons and amino acids

Measuring the Past

The Earth was formed about 4.6 billion years ago

This massive time frame is divided into multiple “eras”

Precambrian, Paleozoic, Mesozoic and Cenozoic

Eras divided into “periods”

Further subdivided into “epochs”

Historic time encompasses only the last 10,000 years of this time frame

Measuring the Past

The divisions between eras periods, etc., represent times of transition in life forms

Many of these transitions are due to major extinction events

e.g., The Cretaceous Extinction marks the boundary between the Cretaceous and Tertiary periods

Largely caused by the impact of a giant asteroid

Extinction of the dinosaurs

Measuring the Past

We will discuss “notable events” in the history of life on Earth

Our choice of what is “notable” is subjective

We will discuss many events in our own evolutionary past

Evolution IS NOT a march toward the formation of humans

We could just as easily discuss events in the evolutionary history of the common dandelion

19.2 How Did Life Begin?

The early Earth was very hostile

Covered with a layer of molten rock

Bombarded by comets, asteroids, etc.

Contained gasses such as methane and ammonia

Spewed from volcanoes, released from deep-sea vents, etc.

By 3.8 billion years ago, the Earth’s environment became less hostile

Black Smoker

Black Smoker Video

Black Smoker Video

How Did Life Begin?

The basic organic molecules present in life can be spontaneously assembled from methane, ammonia, and similar gases

This can be recreated in the laboratory

Similar to what is seen at Yellowstone

How Did Life Begin?

Where this assembly took place is the only question

Life may have arisen in the “prebiotic soup” of a hot water system

Life may have arisen within the sand and silt of ancient beaches

Early Life

Yellowstone Thermal Features

Yellowstone Thermal Feature

How Did Life Begin?

Life did not originate in a single step

The ability of a molecule to self-replicate is one critical feature of life

RNA was most likely the earliest self-replicating molecule

Served as the genetic material

Errors in self-replication produced genetic variation

How Did Life Begin?

Once life was established, forms of life evolved

The earliest branchings produced three domains

Bacteria, Archaea, and Eukarya

Each of these domains branched further to form multiple kingdoms, etc.

e.g., Eukarya branched into four kingdoms (Protista, Plantae, Fungi, and Animalia

The Precambrian Era

The Precambrian Era stretched from the origin of the Earth until 542 million years ago

Many notable events occurred during the Precambrian Era

Origin of life

Origin of photosynthesis

Origin of eukaryotes

Origin of multicellular life

The Precambrian Era

The Earth was formed 4.6 billion years ago

4,600 million years ago

The earliest evidence for life is 3.7 – 3.8 billion years old

3,700 – 3,800 million years ago

Chemical signatures of life exist in ancient rocks

The Precambrian Era

For the first 2 billion years in the history of life, all life was either archaea or bacteria

2,000 million years

The earliest life subsisted mainly on organic matter from their surroundings

This supply was limited

The Precambrian Era

Photosynthesis arose in bacteria by 3,400 million years ago

Energy from the sun was used to produce organic molecules

A large amount of energy-rich food was made available

The Precambrian Era

Cyanobacteria produced oxygen as a product of photosynthesis

Oxygen gas was virtually absent in he atmosphere until 2,400 million years ago

Production of this oxygen drastically changed the Earth’s environments

“Oxygen holocaust”

Organisms unable to adapt to this changed environment died

The Precambrian Era

Many organisms did adapt to the presence of oxygen

Many ancient bacteria were able to metabolize oxygen

The Precambrian Era

Some of these bacteria took up permanent residence in early eukaryotic cells

“Endosymbiosis”

These bacteria became mitochondria

Organelles of eukaryotic cells

Oxygen is used to harvest energy from food

The Precambrian Era

Some cyanobacteria also took up residence within eukaryotic cells

“Endosymbiosis”

These bacteria became chloroplasts

Organelles of eukaryotic cells

Perform photosynthesis

The Precambrian Era

The oxygen produced by photosynthesis reacted to form ozone

Rose through the atmosphere to form the ozone layer

Protects life from the damaging effects of ultraviolet radiation

This protection was important in allowing the colonization of the land

The Cambrian Explosion

Throughout much of the Precambrian Era, many forms of life were present

Archaea

Bacteria

Many types of protists

Early animals appeared near the end of the Precambrian Era

600 million year-old animal fossils have been found

The Cambrian Explosion

The Cambrian Period began 542 million years ago with the “Cambrian Explosion”

Lasted only approximately 6 million years

Produced incredible diversity of animal life

Many new animal forms appeared in the fossil record during the Cambrian Explosion

First fossil evidence of 35 of the 36 currently existing animal phyla

Some extinct phyla appeared then also

The Cambrian Explosion

Did the Cambrian Explosion represent an explosion of forms large and hard enough to leave fossils?

Some divergence of animal forms occurred prior to the Cambrian Explosion

What caused the Cambrian Explosion?

The rise in atmospheric oxygen is a likely cause

Larger organisms would require more oxygen

Movement onto Land:

Plants First

Plant-fungi combinations were the first multicellular life to colonize land

Occurred between 460 million and 1,300 million years ago

Most modern plants have a mutually beneficial relationship with fungi

Plants supply food through photosynthesis

Fungi aid in water and mineral absorption

Movement onto Land: Plants First

Primitive land plants evolved from algae

“Bryophytes”

Represented by today’s mosses

No vascular tissue to transport water and nutrients

Cannot grow very tall

Movement onto Land: Plants First

Early vascular plants evolved from these bryophytes

Represented by today’s ferns

Possess a vascular system

Transports water and nutrients

Affords support and allows taller growth

Movement onto Land: Plants First

Some seedless vascular plants grew quite tall

These were the dominant large plants during the reign of the dinosaurs

Seed plants evolved from seedless vascular plants beginning 350 million years ago

Movement onto Land: Plants First

Gymnosperms are the living descendents of these early seed plants

e.g., Pine and fir trees

Decreased dependence on water

Sperm are packaged into pollen grains

Carried by wind instead of swimming through dew to get to the egg

700 species alive today

Movement onto Land: Plants First

Flowering plants evolved from these early seed plants beginning 165 million years ago

“Angiosperms”

Flowers aided in reproduction of these plants

260,000 species alive today

Animals Follow Plants onto the Land

Vertebrates evolved in the oceans

Gnathostomes evolved 450 million years ago

First jawed animals

Ancestral to all modern fish

New foods became available with the evolution of jaws

Animals Follow Plants onto the Land

Early fish were ray-finned

Lacked bones in their fins

Typified by walleye, etc.

Lobe-finned fish evolved from ray-finned fish

Possessed bones two pairs of fins

Lobed fins are precursors of four limbs

Amphibians evolved from lobe-finned fish

Amphibians are “tetrapods”

Possess four limbs

Animals Follow Plants onto the Land

Amphibians evolved from lobe-finned fish

Retained a major dependence on water

Amphibian literally means “double life”

Spend some of their life in the water and some of their life on land

Notably, their eggs are laid in water or other moist environments

Animals Follow Plants onto the Land

Reptiles evolved from amphibians

Reptiles produce an “amniotic egg”

Membranes within amniotic eggs supply nutrients and remove wastes

Hard outer casing protects them from drying

Amphibian ties to water were severed

Reptiles could move inland

Animals Follow Plants onto the Land

Dinosaurs evolved from one branch of reptiles about 220 million years ago

220 million years ago

Dominant vertebrate for 155 million years

Mammals arose from another branch of reptiles shortly after the dinosaurs arose

210 million years ago

Possessed fur and mammary glands

Animals Follow Plants onto the Land

Early mammals were rather small

Lived in the shadow of dinosaurs for over 100 million years

Began an adaptive radiation near the end of the Cretaceous

The Cretaceous period ended with an asteroid impact that killed the dinosaurs 65 million years ago

Mammals radiated into many recently vacated niches

Animals Follow Plants onto the Land

Primates evolved from ancestral mammals between 55 and 90 million years ago

Key characteristics of primates

Large, front-facing eyes allowing binocular vision and enhanced depth perception

Limbs with opposable first digits

Tree-dwelling existence

The Evolution of Human Beings

Humans and chimpanzees share a common ancestor approx. 6 –7 million years ago

It took more than a single speciation to give rise to humans from this common ancestor

Numerous human-like species have been discovered

The human evolution tree is more of a bush

The Evolution of Human Beings

Taxonomic grouping Hominini

The relationships between these species are not perfectly understood

Major disagreement over which are ancestors and which are “cousins”

Nearly all of the evolution of hominins occurred in East Africa

Some species migrated from Africa to other continents (e.g. Homo erectus, Homo sapiens)

The Evolution of Human Beings

Toumai fossils

Helped push root of hominin family tree back 2 million years

Oldest fossils previously found dated to 4.4 million years old

Date shortly after the divergence of human and chimpanzee lineages

May actually belong in chimp lineage

The Evolution of Human Beings

Australopithecus afarensis

Ancestral to Homo lineage

Best known through “Lucy”

Largely intact skeleton discovered in Ethiopia in the 1970s

Bipedal (known from pelvic structure)

Long arms, short legs, grasping feet

Brain size similar to chimpanzee

450 cc (Homo sapiens is 1,400 cc)

The Evolution of Human Beings

Homo ergaster

Ancestral to Homo erectus and Homo sapiens

Brain over half volume of Homo sapiens

Modern face, limbs, height, advanced tool technology

“Turkana boy”

Best-preserved remains of Homo ergaster

9 years old at death

1.6 million years old

The Evolution of Human Beings

Homo neanderthalensis

Lived 200,000 – 27,000 years ago

First extinct hominin fossils found (1856)

Short, stocky, powerfully built

Heavy brow ridge, receding chin

Brain size slightly larger than Homo sapiens

Tool technology, burial of dead

Likely descended from Homo ergaster

Not ancestral to Homo sapiens

The Evolution of Human Beings

Modern Homo sapiens

Evolved modern anatomical form in Africa before migrating

Arose from 100,000 – 200,000 years ago

Migrated to Indonesia, etc. by 46,000 years ago (coexisted with Homo erectus)

Arrived in Europe 40,000 years ago (coexisted with Homo neanderthalensis)

Homo sapiens replaced them – likely through competition

The Evolution of Human Beings

Homo floresiensis

“Hobbit people”

Discovered in 2004 on the Indonesian island of Flores

Lived as recently as 18,000 years ago

Three feet tall as adults

Cranial capacity of 380 cc

Bain size similar to “Lucy”

Used fire and sophisticated tools

The Evolution of Human Beings

Appeared in the literature 2006

Nothing like it before

Debate:

Diseased population

Preserved older

Normal variation

The Evolution of Human Beings

Homo floresiensis

This species raises some interesting questions

How did Homo floresiensis avoid extinction for so long?

How could they be so sophisticated in their tool and fire use with such small brains?

Did they evolve from Home erectus?

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download