Evolution Lecture 7 Flashcards
(43 cards)
Fossils
Preserved remnants (or traces) of past life in rock. Some examples are:
– Mineral components
– Petrified organic material
– Casts
– Trace fossils (footprints etc)
It tells us information about past ecosystems; climate;
sea levels etc., & dating of geological record. More direct view of evolutionary history than from living organisms. They are biased for species the existed for a long time.
Sedimentary Rock
Where most fossils are found. They are found in the bottom of lakes, layers keep adding show a passage of time. Where mineral particles fall into the water bodies then form layers (other dead animals can get trapped here then are in the rock before they fully decay). They then get compared by heat into solid rock over many years.
Why is the sedimentary rock slanted?
Because it’s very very old.
Where can fossils also be found?
Frozen in ice or in amber (tree sap).
Strata
Sedimentary rock layers.
Archaeopteryx
Fossil of a dinosaur with feathers seen in it. It’s an articulated fossil because it’s all intact.
Index Fossil
Common, widespread fossils characteristic of particular periods of earth’s history. Crucial for ‘relative dating’ in geological record. Eg. shells of single cell organisms.
What can we find out about extinct things from extinct?
Their biology and age.
The geological record
The fossil record is in this. There is a relationship between them. Earth is ~4.6 billion years old. (Microbial) life arose ~3.5+ billion years ago. Fossils of animals & plants common in the last ~550 million years: “Phanerozoic Eon.”
Phanerozoic divided into three what?
Eras
Each Era subdivided into several what?
Periods
The three Eras in order?
Paleozoic, Mesozoic, Cenozotic. This is the last 15% of earths time.
When were the eras worked out?
In the 19th century using many different dating methods, such as index fossils. 20th century use radioactive decay allowed to be sure if date rocks.
Radioactive Decay
Radioactive parent isotope decay to a daughter isotope at a charcuterie rate.
Half-life
the time required for 50% of the parent isotope to decay.
Periods
Subdivisions of eras. They aren’t the same length.
How did the period change occur?
Saw a sudden change in the geological record, where the fossils in rocks changed into different rocks. (the eras change is the same but with bigger differences).
Mass extinctions
Many species extinct in very short time. Causes: large environmental changes. Plausible examples:
– Massive volcanic activity
– Impact by asteroid or comet
Major importance in history of life. Extinction occur all of the time. Only the survivors can speciate.
How many mass extinction are there?
5 big ones, most marking ends of Eras/Periods.
End-Permian mass extinction
~250 million years ago. Most devastating mass extinction. Extinction of ~90% of species on earth. Many large taxa went totally extinct (e.g. ~50% of Families). Guessed that it was caused by volcanoes.
End-Cretaceous mass extinction
~65 million years ago. Most recent ‘big’ mass-extinction. Extinction of ~50% of species on earth
e.g. dinosaurs (other than birds). Several marine invertebrate groups. An astroid hit, the dust from it would block the. sun, this would stop photosynthesis, and food chains.
Adaptive radiations
Rapid speciation and evolutionary change in underexploited habitats. They have a small # of competitors. Many species come to be in a short period of time. They start to differ from each other very quickly.
Two types of Adaptive radiations
Regional: Eg. colonisation of new island chains
World-wide: It can recover diversity after a while.
– Following mass extinction events.
– Only surviving lineages can radiate!
– Replacement in fossil record
Hawaiian ‘Silversword alliance’ example?
Plant group, endemic to Hawaii (very isolated, ‘young’ island group formed by volcanic activity). ~50 species; great variation in size, shape. All descended from one species, in last ~5 million years. the species are genetically similar to each other.
