Unit 7 Topic 3.2: Early Life - Drive to Diversity Flashcards
1
Q
What type of environment did the first life form thrive in?
+ do we have evidence?
Early Life - Paleontological Evidence
A
- This first life form must have lived in an oxygen-free environment (oxygen would not be abundant until well after life evolved), composed of a single cell, and been less sophisticated than the simplest prokaryote on Earth today.
- Given that we have no fossil evidence (yet) of this microbe, what is the oldest evidence we do have? Stromatolites
2
Q
Stromatolites
How are they formed?
A
- Formed by layers of microbes that live on the ocean floor, which secrete a sticky substance that holds them together and traps sediment.
- As tides come and go, more sediment is added, and the microbes move upward to create new layers. This process forms a layered, dome-shaped structure
- The warm, salty water there protects the microbes from grazing organisms, allowing the stromatolites to form
3
Q
Are stromatolites “body fossils”?
A
- NO
- The microbes that produced the structures are not preserved, just the domes and laminations they left behind.
4
Q
What are stromatolites classified as?
A
- As such, stromatolites are often classified as “trace fossils,” the trails or traces of the activity of life
- (In the same way, dinosaur footprints are also “trace fossils” and not “body fossils.”)
5
Q
Australia - Strelley Pool
The Oldest Body Fossils
A
- A preserved shoreline where stromatolites grew in shallow water
- Also contains microscopic fossils (microfossils) that are considered to be true ‘body fossils,’ the preserved remains of once-living creatures
- 3.43 billion years ago, these microfossils were microbes that lived between sand grains on a beach.
- Unlike some older and more controversial fossils, these are generally accepted as genuine life forms
6
Q
Why are the stromatolites in Australia - Strelley Pool considered a genuine life form?
What ‘biogenicity’ tests to they pass?
A
-
They look like microbial structures we are familiar with today
- They exhibit biological behaviour similar to microbes living in similar environments today, attached to and living in the spaces between sand grains.
- The mineral pyrite (fool’s gold) provides evidence of cell metabolism.
7
Q
How do some microbes at Strelley Pool use sulphate reduction to produce energy?
A
- In this metabolic process, the microbe reduces sulphate (SO4) from seawater and releases hydrogen sulphide (H2S) as a waste product.
- The H2S would then react with iron (present in solution in the anoxic oceans of that time) to produce pyrite (FeS2).
8
Q
2 Isotopes of Carbon
A
- carbon-12 (12C)
- and the heavier, carbon-13 (13C).
9
Q
Which of the two isotopes of carbon do plants/microbes prefer?
+ what does this lead to?
A
- Plants and photosynthetic microbes favour CO2 that has carbon-12 because it’s lighter and easier to use in biological processes.
- This preference leads to a higher concentration of carbon-12 (fractionation) in organisms that photosynthesize or eat those organisms.
10
Q
Jack Hills zircons
A
- The carbon in these zircons is enriched in the lighter carbon-12 isotope, suggesting biological processes formed it.
- The carbon was likely produced by microbial life, deposited in sediments, buried to form sedimentary rock, and subsequently melted at some point to form a magma.
- When the magma cooled and formed an igneous rock, the zircons crystallized and trapped some of this isotpoically light carbon.
11
Q
When did multicellular life become more prominent?
A
- It wasn’t until about 560 million years ago that multicellular life became more prominent and easily visible to the naked eye.
- This rapid shift towards a more modern-looking biosphere with familiar phyla is a significant event
12
Q
What is a phylum?
A
a broad classification of animals; for example, humans, lizards, and fish belong to the phylum Chordata, while insects and crustaceans are part of the phylum Arthropoda.
13
Q
During what period did all major animal phyla appear?
A
- The base of the Paleozoic era highlights the short period during which all major animal phyla appeared compared to the rest of Earth’s history.
14
Q
Which timeline events were most significant to phyla?
A
- Even though there were precursors of some phyla in the Precambrian (the Ediacaran Explosion), the Cambrian explosion was a sudden and impressive event.
- Since then, new species, genera, and other taxonomic groups have evolved, but no new phyla have appeared.
15
Q
What followed the Cambrian explosion?
A
- Following the Cambrian explosion, the Great Ordovician Biodiversification Event further increased the complexity and diversity of life on Earth.
16
Q
all creatures composed of multiple cells are called…
The Ediacaran Explosion
A
Metazoans
17
Q
Where are some of the oldest large Metazoans found?
A
- Newfoundland, Canada
- Mistaken Point
18
Q
Mistaken Point - “creatures”
+ how were they preserved?
A
- Mistaken Point preserves a complete ecosystem of creatures in their original living environment
- These creatures lived in the deep, dark water below the photic zone, the depth where sunlight can penetrate the water.
- The rocks are now mudstone but were originally muddy sediments.
- A volcanic eruption nearby buried these creatures in ash, preserving them.
19
Q
Mistaken Point - “creatures”
What did zircons allow paleontologists to do?
A
- Paleontologists dated the fossils to 565 million years ago during the Ediacaran Period, the last period of the Precambrian.
- The fossil animals from the Ediacaran Period are called Ediacarans.
20
Q
How are the Mistaken Point - “creatures” unliike any living thing today?
A
- Called Ediacaran rangeomorphs: ‘frond-like’ creatures made up of simple repeating parts.
- These parts are arranged in a fractal pattern, a simple but effective way to create large bodies from small, self-repeating components.
- These creatures were stationary (sessile), unable to move.
- They likely required only 7 or 8 genetic instructions to develop, compared to the over 25,000 needed for humans.
21
Q
What are the Mistaken Point - “creatures” missing? (2)
A
- Ediacaran rangeomorphs show no signs of a mouth or digestive system.
- Some scientists believe they were osmotrophs, absorbing nutrients and organic matter directly from seawater through their thin bodies.
- Reproductive organs are also absent. Some may have reproduced by budding or releasing a ‘building element’ into the ocean that would settle and grow into another fractal creature.
22
Q
Younger Ediacaran fossils dating to 550 million years ago (but still within the Edicaran Period) are found in Australia.
What three important innovations do they demonstrate?
A
- a greater diversity of body plans (including bilaterally symmetrical animals)
- an ability to biomineralize (make shells)
- an indication that the biosphere was no longer fixed on the ocean floor and could move around.
23
Q
The Cambrian explosion is typically linked to…
The Cambrian Explosion
A
the emergence of biomineralizing animals that produce hard parts like shells.
24
Q
Why have paleontologists considered the “Cambrian Explosion” as extending across the Cambrian-Precambrian boundary?
A
- Some biomineralizing organisms were present in the Ediacaran, leading many paleontologists to consider the “Cambrian Explosion” as extending across the Cambrian-Precambrian boundary
- Consequently, the Ediacaran and Cambrian explosions overlap to some degree.
- EX: Cloudina - SSF fossils (Small Shelly Fauna) were found in the Ediacaran, they rapidly diversified in the early Cambrian.
25
What emerged after the small shelly fossils?
* The emergence of large animals, like trilobites
* NOTE: only the **Phylum Cnidaria** (jellyfish and corals) and the **Phylum Porifera** (sponges) have been definitively identified from the Precambrian.
26
Have new phyla appeared since then?
* While new species have evolved within these phyla, **no new phyla have appeared since then**, making the Cambrian explosion one of the most significant and intriguing parts of Earth's history.
* A question that we don't have time to answer is WHY the Cambrian explosion happened.
27
What significant diversification event occured after the Cambrian period?
Unlike the Cambrian Explosion, the **Great Ordovician Biodiversification Event (GOBE)** saw diversification within the existing phyla that emerged during the Cambrian.
28
What resulted from diversification in the GOBE? (2)
* This resulted in a threefold **increase in animal families**, leading to a **dramatic increase in overall biodiversity**.
* This diversification **also created more complex food chains and ecological relationships between organisms**, replacing the arthropod-dominated world of the 'Cambrian Marine Fauna' with the '**Paleozoic Marine Fauna**' **that would generally characterize the biosphere until the Permian Extinction Event** at 252 million years ago.
29
What were some causes of The Great Ordovician Biodiversification Event (GOBE)?
* Global warming & rising sea levels
* Flooding of low-lying areas with seas (favourable conditions for photosynthetic plankton)
30
Global warming and rising sea levels were significant - why?
## Footnote
What were some causes of The Great Ordovician Biodiversification Event (GOBE)?
* **Continents were fragmenting**, leading to increased tectonic and volcanic activity.
* **Volcanic emissions raised atmospheric carbon dioxide levels**, warming the planet.
* **Polar ice caps melted**, and **warmer water** expands, further contributing to rising sea levels.
* Higher sea levels may have been due to the **increased number and activity of spreading ridges**; active spreading ridges are broad, occupying more volume on the ocean floor and displacing more water from the oceans onto the continents.
* These **warmer conditions would also have allowed for increased rock weathering** on the continents, increasing nutrient flow into the oceans.
31
How did global warming create favourable conditions for photosynthetic plankton
* The flooding of low-lying areas with warm, tropical, nutrient-rich seas created favourable conditions for photosynthetic plankton to flourish, **increasing oxygen levels.**
* The **increased plankton diversity also drove the evolution of filter-feeding organisms and their predators.**
* The greater continental fragmentation also promoted evolution, as **deep oceans can isolate marine creatures in shallow seas, leading to independent evolution**.
32
Other impacts of warm oceans on the GOBE
* Another significant impact of these shallow, warm tropical oceans was the **evolution of corals and the development of coral reefs**
* As is the case today, coral reefs are the tropical rainforests of the oceans and hot springs of evolution.
33
What initiated the End of the "Tropical" Ordovician?
## Footnote
What is hypothesized?
* A dramatic biodiversity shift occurred—**a mass extinction event** that wiped out an estimated 49-60% of genera and around 85% of species on Earth.
* While the exact cause remains debated, the most compelling evidence points to **a period of extreme climate change—a global glaciation event.**
34
What and where was the global glaciation event?
* The culprit is the supercontinent Gondwana, which encompassed much of the southern hemisphere, drifting towards and eventually reaching the planet's south pole (Figure 10).
* Geological evidence suggests a major glacial period gripped Gondwana, setting off a chain reaction.
35
What was the chain reaction for Gondwana?
Global temperatures plummeted as the southern hemisphere froze, shifting Earth from a warm greenhouse climate to a colder icehouse state.
36
What resulted from the drastic cooling of Gondwana?
* First, **organisms adapted to the warm Ordovician seas struggled to survive in the colder oceans**. Shallow tropical habitats, once teeming with life, shrank significantly as the polar front expanded.
* Second, **the formation of glaciers trapped vast amounts of water**, causing sea levels to fall.
* **This shrinking of shallow continental seas eliminated the habitats of many marine organisms**, particularly those biodiverse reef communities.
* **This drop in sea level is visible in the geological record as disconformities**, which mark the withdrawal of the sea and the formation of an erosion surface.
37
Was the mass extinction a single event?
* **NO**: The fossil record shows two distinct phases.
* **The first wave coincided with the onset of glaciation**, followed by a period of relative stability.
* **The second pulse occurred as the glacial period ended; the climate *began to warm again*, and anoxic (low-oxygen) conditions developed in the oceans.**
* This anoxia may have been caused by an algal bloom associated with the warming conditions.
* **As the algae died and sank, they consumed much of the ocean's oxygen during decomposition.**
* The impact wasn't limited to the deep ocean; the expanding oxygen-depleted zones shrank the habitable zone for marine life, leading to more extinctions.
38
How is a mass extinction event classified?
## Footnote
Mass Extinction Events and Diversity
* A mass extinction event is classified as such **when around 10% of families (equivalent to around 30% of species) go into extinction over a geologically short period of time (tens to hundreds of thousands of years).**
* The extinction must also be recognized globally, occurring in many ecosystems and impacting many different types of organisms.
39
How many extinctions happened during the Phanerozoic?
* Five mass extinctions during the Phanerozoic, with the largest being the **end-Permian event**, where it is estimated that 57% of families and perhaps more than 90% of species were driven into extinction over a period of just 60,000 years.
* It is thought this was the result of runaway global warming.
* The Permian extinction event cleared away much of the Paleozoic fauna and allowed for the emergence of a biosphere more similar to today's.
40
What are the "pros" of extinctions?
* **Extinctions clear ecological niche space and allow for the diversification (radiation) of new forms.**
* For example, the end-Triassic extinction (201 million years ago) paved the way for the diversification of dinosaurs, which dominated the rest of the Mesozoic Era. Similarly, the end-Cretaceous extinction event (66 million years ago) removed non-avian dinosaurs and marine reptiles, creating ecological opportunities for mammals to radiate during the Cenozoic Era.
