ASTR-301 Lessons

Welcome!  Today is the final installment in the story of our planet.  That is not to say that the story is finished, but the next chapter is yet to be written by both the universe and yourselves.  Here is where it all comes together: it is the story of us.

A Spark

Almost four billion years ago, during the Hadean period, Earth looked very little like the Earth we know today.  Continents, created by roiling volcanic activity in the mantle, rose above the waves only to be torn apart by additional volcanic activity.  Around them, water sloshed, covering most of the planet, and steaming where the crust split apart.  The air was a noxious mix of ammonia, carbon dioxide, sulphur dioxide, and water vapour.  Comets, meteoroids, and even asteroids were still falling from the sky much more often than they do now.  The land and sea were completely devoid of life.

Let us imagine we could take a Time-Turner all the way back to this time; we would need a Bubble-Head Charm to protect us from the harsh conditions of the new Earth.  We find ourselves on the edge of a huge continent.  A younger Sun shines down upon us; it is much warmer too, as the atmosphere here traps far more heat than today’s atmosphere.  Behind us a volcano oozes lava down its sides, ash and hot gases billowing from the top.  Clouds of sulphurous steam obscure the nearby coastline where the lava meets the ocean.  The rocks beneath our feet are scorched and barren: heat, solar radiation, and asteroid impacts have made it impossible for life to take hold here.

Barren Rocky Landscape

Source: here

This strange world is also a land of pure and wild magic.  Stone is able to absorb a great deal of it, but it cannot transform this energy into light or heat.  The quantity of magical energy both radiating from the Sun and being released by volcanic activity is too great to be completely absorbed by the metals and rock that make up the Earth’s surface. As a result, there is a great deal of wild magical energy surrounding everything.  Performing even the most basic spell in this environment would result in a massive backfire.  You would need to keep your wands safely tucked away here; there is too much power to be controlled by any witch or wizard.

The ocean is entirely different.  Here, the wild solar magic has been tamed by the water, which also provides protection from light and solar radiation.  Thanks to this protection, this is where many different complex molecules have formed and thrived.  Instead of clear, turquoise waters, this ocean is a primordial soup, filled with all the building blocks of life.  It’s getting a bit uncomfortable on land so let’s all dive in and take a closer look: I have a feeling something big is about to happen!

The light from the Sun isn’t so harsh down here, and it’s cooler too.  You almost feel alone under the surface.  Almost.  It happens in a moment, in half an instant - suddenly you’re not alone anymore.  It starts with one cell, one tiny organism; it will soon be joined by many others.  This particular single-celled organism does not interact with or possess any of the tame magical energy surrounding it; it is the first mundane life on Earth.  That underwater vent over there, however, is spewing more than just heat, gas, and ash into the water.  It is also releasing magical energy in excess.  The cells coming together there are not only adapted to magical energy, they have some themselves: they are the first magical life on Earth.

Underwater vent  

Source: here

I hope you enjoyed your trip into the past.  Now let’s use the time turner to return to the present time.  While magical bacteria do grow around volcanic vents, some non-magical ones do too; these bacteria have actually developed a resistance to the magical energy of the Earth.  Magizoologists and magical biologists are still studying these magic-resistant bacteria, known as “super-mundane bacteria” to see what effect they have on the ecosystem.

The first life on Earth came to be because of a specific set of circumstances.  Excessive heat and radiation were too harsh for complex molecules to exist. However, they could thrive in the one place where they were protected from those damaging effects: water.  You’ll see that it continued to evolve to what it is today under similarly particular conditions.

Humans: A History

The very first life on Earth, both magical and mundane, was extremely simple. Amino acids in the sea water came together to create an organism called cyanobacteria.  These blue-green algae were also the first producers of oxygen.  They and their various relatives would eventually transform Earth’s atmosphere into the oxygen-rich environment we know today.  It would, however, take a further billion years before the organisms of Earth could begin to use oxygen to breathe.

Blue-green algae  

Source: here

Approximately one and a half billion years ago, single-celled organisms on Earth underwent another significant change.  They developed complex cellular organs, such as the nucleus: a cell’s “brain” and the common feature between all plant, animal, and fungus cells.  At this time, all life reproduced asexually.  This meant that a single cell would produce a copy of itself instead of combining its genetic material with another’s.  This allowed the organisms to flourish, though it offered little genetic diversity.  The result of this was that these organisms were unable to easily adapt to changing environments and, consequently, they stayed in the water instead of expanding their habitats outside of the ocean.  Another 500 million years would elapse before the first sexual reproduction would occur, allowing organisms to adapt more easily to foreign environments.

It is around that time that life became more complex.  Instead of single-celled organisms, cells began to collect and form multicellular organisms.  Plants were able to grow relatively easily, as  having many cells allowed the plants to produce more food and energy from sunlight, while genetic diversity allowed them to adapt and evolve around changing environments.  

Life on Earth has always moved forward, but that does not mean that the journey has been an easy one.  Several mass extinction events have changed the face of life on Earth.  The first mass extinction occurred in the Cryogenian Period and killed approximately 70% of all marine plants when the Earth and its oceans cooled below survivable levels for these early plants.  Despite this disaster, we see that life continued to develop with the first soft-bodied organisms, such as jellyfish, and shelled invertebrates appearing in our oceans.

The Paleozoic Era saw life flourish all over our planet.  Marine invertebrates (animals without backbones) were joined by the first vertebrates (animals with backbones), while small green plants and fungi made the transition from ocean to land.  This achievement was dampened somewhat by a mass extinction in the Ordovician Period, when cooling oceans killed many marine invertebrates. Nonetheless, the first vertebrates persisted by adapting to this climate change and developing features such as jaws.  These vertebrates were fish, which became the first sharks, beginning their 450-million-year reign in the world’s oceans.  Spiders and centipedes also made their way onto land during this era, though this was fortunately overshadowed by the appearance of Tiktaalik, the first vertebrate with legs, who also made it onto land, and evolved into other amphibian species such as the ones shown in the image below this one.

Tiktaalik

Source: here

Amphibians. Clockwise from top left: Leaf Green Tree Frog, Seymouris Baylorensis, Mexican burrowing caecilian, and eastern newt. 

Source: here, here, here, and here

Many varied plant and animal species made their homes on land, even as more diverse life came to being in the oceans.  This great progress was almost derailed completely during the Permian-Triassic mass extinction.  A massive asteroid struck the Earth around this time, and the resulting climatological changes killed almost 90% of all marine life and 70% of life on land.

This mass extinction halted progress in one direction but enabled life to move forward in another: it paved the way for lizards, birds, and even small mammals. About 225 million years ago, vertebrate life finally took to the skies when the first flying dinosaurs appeared (flying insects had been around since 500 million years ago).  It was at this point that vertebrates had completely conquered sea, land, and air.  Much later we see the arrival of life that looks far more similar to the life we know today.  Plants began producing flowers and fruit while birds’ beaks lost their teeth.  Crocodiles, another ancient creature, first appeared about 100 million years ago and, like sharks, have continued to thrive up until today.

In that time, Pangea (which, if you remember back a few lessons, was the supercontinent that broke apart to become the continents we know today) formed and broke apart.  When Pangea began to split, dinosaurs ruled the Earth. Massive forests were filled with similarly massive creatures. As these animals died from predators and natural causes, their bones were slowly replaced by minerals, creating the fossils we see in museums and private collections today. The distribution of these fossils and petrified trees (trees that have undergone a similar process of fossilisation) across the continents shows us where these animals lived on Pangea and gives us insight into how the supercontinent separated and land masses moved over time.

Continents move very slowly, usually only a couple centimetres a year, meaning the climate changed very slowly for those continents that moved towards the poles.  Creatures on these land masses had time to change and adapt to their surroundings. We could very well still have Tyrannosaurus rex-type creatures roaming the world today if it had not been for the Chicxulub asteroid impact.

Tyrannosaurus rex

Source: here

This is the final mass extinction event and occurred at the end of the Cretaceous Period. The impact was so massive that it triggered tsunamis, volcanic eruptions, and earthquakes; dust and ash filled the sky, blocking sunlight and lowering global temperatures.  Unlike the slow moving change of continental drift, these changes happened too quickly for the dinosaurs to adapt.  Over 80% of all life on Earth was extinguished 65 million years ago.  Dinosaurs that needed a great deal of energy and sunlight to thrive were unable to cope with the harsh conditions except for a few magical pterodactyls that were able to survive by catching prey that had become sparse.  They eventually evolved into dragons - but more on that on a different day.  Mammals, on the other hand, saw this as their chance to thrive.

Mammals at this time were very small - the size of small rodents today.  They were able to adapt to the harsh new climate, however, because they were warm blooded and had fur, which made them less reliant on the Sun for energy.  Their small size also meant that they didn’t need to consume as much food, which was helpful when resources were scarce.  It would take another 65 million years, however, before these mammals evolved into the many species of mammals we see today.

It was not until about six million years ago that the first upright hominids appeared.  These ancestors of ours were the result of the unmatched survival of many different species throughout the aeons.  At each step, these species had to overcome predators and natural disasters, changing climates and ecosystems, all to become something that vaguely resembles us.  It was only within the last million years that hominids mastered fire, speech, magic, and the environments in which they lived and it has been only about 300,000 years since our species, Homo sapiens, appeared on Earth.  Today we are the most dominant species on the planet, but we all came from a handful of cells in a barren ocean millions of years ago.

A Family Tree  

All life on our planet began with the single-celled organisms that appeared relatively soon after the Earth formed.  How, then, did we end up with the many different species of plants and animals that exist today?  The answer is evolution.

Evolution is the process by which living things gradually change and adapt to the world in which they live.  While we can see the big changes between species over a very long period of time when we compare, say, a woolly mammoth to an elephant, the changes are very difficult to see from one year, or even one decade, to the next.

Evolution of elephants  

Source: here

Evolution occurs most often in reproduction.  In sexual reproduction, DNA, the chemical code that determines all features of an organism, is combined from two different animals of the same species.  The male and female each give their offspring half of their DNA, which combines to form a whole DNA blueprint for the new organism being created.  

Sometimes the two halves don’t come together perfectly, a parent’s gene fails to copy correctly, or a gene gets changed by a chemical agent or radiation, resulting in tiny changes in the offspring compared to their parents.  Most of these changes, which are called mutations, are harmful and result in the organism dying relatively quickly. However, about one percent of these changes allow the new creature to grow and thrive better than its parents; the new organism has a better chance of surviving to pass these traits on to the next generation.

These changes to DNA affect more than just a single organism - eventually two familial lines of creatures of the same species, but different DNA changes, can become two entirely different species, though this takes a very long time. Sometimes nature chooses which genes - specific parts of DNA - survive, and sometimes humans get to choose. This can be unconsciously, such as when early humans domesticated the tamest wolves, resulting in their evolution into dogs. It can also be consciously, for instance when modern humans breed pest-resistant plants.

The process by which nature chooses is called natural selection.  When changes to DNA are helpful, that change is more likely to be passed on. The brazier to my right contains fire salamanders, while the bowl to my left contains frost salamanders.  Both species are amphibians.  Their mundane amphibian cousins are notable because their skin must always be in contact with water. Similarly, these two magical varieties require fire and ice, respectively, and depriving them of either will hurt them.  

Amphibians are the second-oldest vertebrates after fish; they were some of the first creatures to leave the water and move to land.  Fire salamanders are also very old, magical descendants of the first land animals.  Electrical storms and volcanic activity created the first fires that these creatures adapted to live in.  As naturally occurring forest fires are still very common, these species have had to change very little over time.  Like sharks, who appear similar to their ancestors, fire salamanders are also living fossils.

Fire salamander 

Source: here

When Pangea began to break apart, certain magical species found their habitats moving from tropical zones to more temperate climates.  Those that could adapt more quickly to cooler temperatures lived to produce more offspring who also had a liking for the cold.  Over 65 million years later, we now have magical salamanders who survive in ice.  While they are also considered living fossils, this ice-loving branch of the salamander family tree is much newer in evolutionary terms.

Frost salamander

Source: here

While salamanders are small enough to bring into the classroom, the same cannot be said of dragons.  While they share a common ancestor - a gigantic, magical, winged dinosaur called Magicosaurus, whose power was strong enough to survive the extinction that killed off their non-magical cousins - dragon species today are all very different.  Some have venom, while others use different temperatures of flame to hunt and defend themselves.  

Natural selection can work fairly quickly to help plants and animals to adapt to more rapidly changing conditions.  The early seas of Earth were fairly warm, owing to the greenhouse gases in Earth’s second atmosphere.  When photosynthesis took off, a large amount of oxygen was generated. Plants that lived on carbon dioxide were poisoned by the oxygen, but a magical plant species began to store that oxygen instead of releasing it. It even used oxygen to power photosynthesis when there was no sunlight. Today, we see several descendants of this magical species.  They are the “Gilly” family, which contains Gillywood trees and Gillyweed, and which you may recognize from Lesson Eight of Year Two Herbology.  The plants in this family survive through photosynthesis powered either by the sun or by stored oxygen.  Its magical properties also mean that when the plant is consumed, it allows you to breathe and move underwater for a period of time.

Gillyweed

Source: here

Evolution takes a very long time, but it will never stop improving the living beings on our planet.  As the seasons change, the continents shift, and the years pass, our Earth’s story grows ever longer; written in the land, the air, the water, and the flora and fauna as they change and grow.  The next chapter of this story will be written many centuries from now.

That will be all for this week.  As usual there will be a short quiz to do and an essay to write.   Next week we will be discussing the possibility of other earths in the universe.

Original lesson written by Professor Gagarina.