Evolution, mass extinction, dating methods and climate change Flashcards
What are lobe-finned fish
Lungfish, had the ability the breathe in and out of water
Lobe-finned fish morphology
Robust fleshy fins with an arrangement of central bones inside which would have allowed for more mobility and support (especially on land) however there was no strenghtining girdle connecting the bones at the extremities to the rest of the skeleton, this gave an area of weakness
Functioning lungs which are a modified swim bladder
what are the similarities between the lobe-finned fish and the early amphibians
The four subs of the lobe-finned fishing the four limbs of the early amphibians skeletal structure were very similar
Their limbs were in the same position on the body
They both lacked claws or nails
Adaptation to life on land
Development of a girdle connecting the limb bones to the skeleton for a better movement on land
More robust skeleton strengthening the vertebral column and rib bones, for support on land
Eyelids formed to help keep eyes moist on land
Tongue formed
Development of a double looped circulatory system with a three-chambered heart to pump mixed blood before and after it had been to the lungs
The amniotic egg
Dinosaurs are believed to have laid amniotic eggs
They are one of the most significant features in reptile evolution as it allowed for life non land without the need for a water source in which to produce
The first advantage for life on land was the development of a hard outer shell which provided protection whilst still remaining porous. This allowed the diffusion of oxygen into the egg and carbon dioxide out, allowing respiration to take place, the yolk sac provided the embryo with food and the albumin supplied water and nutrients
When did dinosaurs begin to evolve
After the perm-triassic extinction wiped out much of life on Earth, they evolved into two separate classes, Saurischia and Ornithischia
What was the Saurischia and Ornithischia divided into
Saurischia was divided into Theropoda (birds and T-rex) and Sauropoda (Diplodocus)
Ornithischia includes the Iguanodon
What did dinosaurs evolve from and at what time period was this
Archosaurs in the Triassic
What are the characteristics of Saurischian dinosaurs
Pubis points forward (similar to reptiles)
They have long S-shaped flexible necks, allowing rapid and precise movement
Hands consisted of only three digits (fingers)
What are the characteristics of Ornithischian dinosaurs
The arrangement of the hip bones similar to birds (pubis points backwards)
The front teeth are small or absent (replaced by a break which later became broader)
Many had bony plates which acted like armour or heat exchangers
Diplodocus (Saurischia, Sauropoda)
Herbivore common in the Jurassic and the Cretaceous, it had a long slender skull which was small compared to the rest of its body
Extremely long neck which it carried parallel to the ground
Teeth were not for grinding so probably swallowed the vegetation whole
Swallowed stones with bacteria to help with digestion of plant matter
Tyrannosaurus (Saurischia, Theropoda)
Carnivore in the late cretaceous
Could of been a predator or a scavenger
Scavenger - Small eyes instead of large eyes, Small arms so couldn’t grab prey, Back legs were huge indicating it was slow however large legs able them to walk far indicating scavenger, Large olfactory lobes which is good for scavenging
Iguanodon (Ornithischia, Ornithopoda)
Appeared in the late Jurassic Large heavy built creature Horny toothless beak Had cheek teeth Was quadrupedal and bipedal using its tail as a counter balance and to run or to rear up and swing its spiked-like thumb in defence
Evolution of birds
Most accepted theory is birds have evolved from Theropods
Hollow thin-walled bones, to make the bones lighter
S-shaped curved neck
Elongated arms and forelimbs, and clawed hands
The pubis shifted from an anterior to a posterior position
Large orbits
Hinged ankles
Archaeopteryx
First known bird-like fossil
Believed to be intermediates between birds and reptiles
What is the most famous mass extinction
The Cretaceous - Tertiary mass extinction be cause it is when the dinosaurs became extinct
Name the mass extinctions through out time
Ordovician - Silurian boundary
An event towards the end if the Devonian
the Permian - Triassic boundary
the Cretaceous - Tertiary boundary
When did the Permo - Triassic mass extinction occur
251 Million years ago, marking at the end of the Palaeozoic Era
What is the hypothesis to explain the Permo - Triassic mass extinction
Super continent formation - At the end of the Permian, Pangea was formed when all the worlds continents collided together, the presence of this massive land mass had several effects, FEWER CONTINENTAL SHELVES SO THERE WAS A LACK OF HABITAT FOR SHALLOW MARINE DWELLERS, SINGLE CONTINENT CAUSED RAPID FLUCTUATIONS IN CLIMATE, WIDESPREAD GLACIATION OCCURRED CAUSING SEA LEVELS TO DROP
Major volcanic activity (Siberian Traps) - largest volcanic eruption in history, EMISSION OF POISONOUS GASSES WOULD KILL MANY PLANTS AND ANIMALS, ASH PARTICLES EMITTED COULD FO LOWERED THE TEMPERATURE, EMISSION OF GREEN HOUSE GASSES
Methane hydrates - global increase in temperature could of cause this to become mobile and distrust life in the seas
What is the hypothesis to explain Cretaceous - Tertiary mass extinction
Impact of an asteroid or a meteorite - 65 million years ago, LAYERS OF IRIDIUM CAN BE FOUND CONCENTRATED IN CLAYS AT THE BOUNDARY AS A THIN LAYER WITHIN THE SEDIMENTS, PRESENCE OF TEKTITES WHICH IS USUALLY FOUND NEAR IMPACT CRATERS THEY HAVE A VERY LOW WATER CONTENT SUGGESTING THE DONT COME FROM EARTH, A METEORITE CRATER CAN BE FOUND ON THE YUCATAN PENINSULA IN MEXICO
Radiometric dating problems, what are they
With SEDIMENTARY rocks, weathering and erosion break the closed systems that is essential for a reliable date, problems are with loss of gasses because weathering had allowed Argon to escape
With METAMORPHIC rocks - different minerals become closed systems at different temperatures, parent/daughter atoms can be lost during heating events
With IGNEOUS rocks - large scale intrusions may take tens of millions of years to cool, different parts reach closure tempetatures at different times
With POTASSIUM-ARGON dating - not so good on rocks that crystallised over a long period of time
With RUBIDIUM - STRONTIUM dating - 87Rb decays to form87Strontium as the daughter isotope, this is a solid and therefore unlikely to be lost from the rock
Relative dating - what are the five main types
Original horizontally Principle of superposition Way-up criteria Included fragments Cross-cutting relationships
What is original horizontality
Most sedimentary rocks originally deposited in shallow seas, these are deposited as beds, with breaks in deposition showing up as bedding planes, these beds are commonly laid down horizontally or very close to horizontal, therefore assumed that if layers of rock are tilted, then they have moved from this original horizontal position.
What is principle of superposition
This principle states that the rocks at the bottom of a sequence are always the oldest and younger rocks were laid down on top of the older ones
What is way-up criteria
these structures can only form one way up and so if these are present we can tell if the rocks have been turned upside down
Desiccation cracks, which dry up with the cracks pointing to the oldest rocks
Graded bedding, where the large particles sink to the bottom first, followed by finer sediment
Rootlets always grow down into soil
Cross bedding, these can only be truncated on the upper surface
Fossils can sometimes be found in life position and so indicate the way they lived
What is included fragments
Fragments eroded from an older rock can be found within younger rock. The fragments have to be older than the rocks that they are found in
Xenoliths found in igneous rocks have to vibe older
Derived fossils are older than the sediments they are found within, have been eroded from older beds and redeposited in younger beds
Pebbles in a conglomerate are older rocks eroded and then redeposited
What is Cross-cutting relationships
Features that cut across rocks must be younger than the surrounding rocks
What is Unconformities
These represent a break in decomposition and erosion of the succession, gap in geological record in which there may be time to fold and erode the older rocks before new sediments are deposited above the unconformity.
What makes a good zone fossil
Evolves rapidly
Are abundant
Easily identified
Have a wide geological distribution
Climate change - What are run way effects
Increased snowfall in a cooler period would reflect more radiation back into space due to high albedo, so temp would drop even further, which would lead to planet being iced over
Small increase in temperature allows the oceans to release more CO2 than they absorb, more CO2 means more ir converted to heat and therefore increase temperatures
What is Milankovich cycles
Cycles are caused by changes in the amount of radiation reaching the Earth from the Sun overtime, not because the sun changes its solar output but the earth orbit around the sun changes in three predictable cycles
What is Eccentricity
The earths orbit changes shape to become more elliptical over a period of 100,000 years
What is Obliquity
Tilt of the Earths axis, which is responsible for changing seasons, changes up to 3 degree, a smaller tilt promotes the growth of ice sheets as warmer winters result in more moisture and snowfall
What is Precession
Eccentricity and Obliquity
What is isostatic change
Changes in sea level due to local subsidence or uplift are isostatic
What is eustatic
Changes in sea level due to changes in the volume of water in the oceans are called eustatic
What are the three main ways of measuring past sea levels
Using seismic evidence to find unconformities where transgressing seas have resulted in the sea laying down younger beds that cover the older strata as the seas deepen
Using exposed geology o estimate the areas of flooded continents through time, the effect of sea-level change are seen on the continental shelf and upper part of the continental slope. When sea level falls there will be raised beaches and cliff lines. When sea level rises then forests will be submerged and marine organisms can be found in younger sediments
Using oxygen isotope ratios to assess the past temperatures and therefore the amount of ice
Geological evidence for sea-level changes in the Pleistocene
Deep-sea micro-fossil assemblages from Atlantic cores of deep-sea sediments with palaeomagnetic dating shows that about 30 glacial events occurred during the Pleistocene
Measurement of the ratio of 18O to 16O in the foraminifera, the ratio show the volume of ice temporarily removed from the system
Study of uplifted coral reef terraces on tropical islands show that sea level was higher in the past
Mechanisms of sea-level change
The volume of water in the oceans has to change or, the volume of the ocean basins is altered
What happens when the is a glacial episode/ice melts
Glacial episode-Regression
Ice melts-Transgression
Mass extinction by falling sea level
Mass extinctions can be caused by regressions, because there is a loss of shallow marine habitat, also the temperature fluctuations that come with it would be very damaging to marine life
Link between mass extinction and transgression
Transgression leads to more shallow-marine habitats, which trigger blossoms of marine plankton, bacterial decomposition of the plankton resulted in high biological oxygen demand and therefore anoxic conditions and mass extinction. we can recongnise these events by appearance of black shales
