The History of Life on Earth
0.overall_final Click that for a poster for all the talks. Useful for advertising.
In this talk, what we know about the early Earth’s geology and atmosphere will be reviewed, using that knowledge as the base on which to discuss the two main hypotheses about how life originated.
This will lead on to a discussion of the earliest life forms on Earth and how they revolutionised atmospheric and oceanic chemistry and forever changed the course of evolution on Earth.
At the end of the Proterozoic, from ~700 to 535.1 million years ago, a unique ecosystem developed inhabited by what is known as the Ediacaran Biota. The affinities of most of these organisms (if they are even organisms!) will always be disputed, but it is relatively sure that among sponges and jellyfish, the direct ancestors of the animal phyla we know today were lurking among them.
The start of the next period, the Cambrian, is dominated by what is known as the Cambrian Radiation, an event in which ecology and animal life as we know it arose in a period of 20-30 million years. The animal phyla of today – chordates, arthropods, echinoderms, etc. – originated in this sudden burst of evolution.
An extinction event at the end of the Cambrian was followed by various radiations and smaller extinctions, during which most of the major orders of animal life originated.
This talk will go from cover 300 million years, from ~700 Ma to ~400 Ma, to review these events. It will be informed by the spectacular fossil localities available from these times, which preserve the unique animals in exquisite detail.
Dry land was at first a dangerous place, with extreme UV radiation being the deadliest threat. Yet in the Silurian, the first plants got established there, and they were soon followed by the arthropods and eventually by the vertebrates. These pioneers had conquered the second great habitat available to the biosphere (and soon enough, the flying insects had the atmosphere to themselves). The first portion of this talk discusses these first organisms and how they adapted to this new habitat.
The few taxa that went on land underwent considerable and rash radiations. Forests unlike those of today spread across the supercontinent Pangaea, inhabited by arthropods who grew to enormous sizes due to the high oxygen levels in the atmosphere. Amphibians had their heyday while the earliest ancestors of reptiles and mammals slowly gained prominence. This period, from the Devonian to the end of the Permian, will be covered in the second portion of this talk.
Dinosaurs are the most well-known organisms from the Mesozoic, the era comprising the Triassic, Jurassic and Cretaceous. However, a common misconception is that the mammals that lived alongside them were all small, unspecialised, rat-like organisms. This is untrue, as this talk will show.
Of course, the end of the Cretaceous is marked by an extinction event that wiped out most of the dinosaurs and set the stage for the terrestrial ecosystems of today. I will review this well-studied event and how the biosphere rebounded from it.
If one were to tally the number of species from every multicellular organism group, the number of insect and flower species would dwarf all the others. This is the result of a co-evolution that has been going on for over 100 million years. This talk will review the diversification of the insects, the origin of the flowering plants, and their long-running relationship.
I will briefly review the origins of several mammalian orders, including whales and primates. However, the last 65 million years of Earth’s history are a perfect showcase for the effect of climate on evolution and the biosphere, and that will be the main focus of this talk, using the ice ages and the mammalian megafauna to demonstrate the effect of climate changes on biogeography and ecology – it should not be forgotten that the modern human’s success is also a product of this.
We are now in an interglacial period, but the past 200 years have seen an unprecedented rate of atmospheric change related to human industrial development. Anthropogenic climate change is a serious threat to biodiversity, affecting not only the biogeography and livelihood of terrestrial organisms, but also putting marine life at risk. The second portion of this talk will look at how global warming will affect the biosphere, should it continue unmitigated.