It’s easy to think, given the current geopolitical state of the world, that we’re living through an especially terrible time. Add to that the possibility that Earth may be undergoing its sixth mass extinction and it’s perhaps justified to conclude that the 21st century is the worst time period ever.
While this may be the case by some definitions, there’s no escaping the fact that we, as a species, have it better than our ancestors and those that came before them ever did. For the majority of Earth’s history, life has simply been a matter of survival. Let’s take a look at some times when staying alive was particularly difficult…
10 terrible times to be alive
The time the ocean lost almost all its oxygen
The Middle Cretaceous may have been a particularly prosperous time for life on land, but under the waves a geochemical storm was slowly brewing – one that would eventually rob the oceans of oxygen and cause the extinction of more than 25% of marine invertebrates, as well as one of the most iconic marine reptiles of the Mesozoic Era, ichthyosaurs.
This calamitous event is known as the Cenomanian-Turonian boundary event and it’s widely considered to be the most recent, truly global oceanic anoxia event in Earth’s history. It happened roughly 94 million years ago following the eruption of a series of underwater volcanoes in the newly formed Atlantic Ocean.
These eruptions released nearly 4 million cubic kilometres of lava (enough to fill the Mediterranean Sea) and enough CO₂ to raise global temperatures by more than 5°C. At the equator during this time, water temperatures exceeded 42°C, which is warmer than those typically experienced in a hot tub! Even water temperatures at the poles were a balmy 20°C.
This period also witnessed massive plankton blooms – caused by an increase in dissolved nutrients as a result of increased rock weathering. When this plankton died it was eaten by bacteria, which consumed lots of dissolved oxygen from the water column.
For more than half-a-million-years, the deeper levels of the world’s oceans were devoid of oxygen, making them inhospitable to almost all forms of life.
The time a tsunami (may have) submerged part of Europe
Not too long ago (around 10,000 years), a land bridge known as Doggerland connected the east coast of the UK to the Netherlands, northwest Germany, and the Danish peninsula of Jutland.
This lowland area was once inhabited by mammoths, cave lions, sabretooth tigers, and several other iconic ice age animals. It was also home to roaming bands of hunter gatherers, as evidenced by the discovery of several artifacts dredged up during trawling missions in the North Sea – the most famous being a 20cm-long harpoon carved from a deer’s antler.
For our ancestors, Doggerland provided some of the continent’s richest hunting grounds, not to mention a bountiful supply of freshwater. However, by 8,000 years ago it had completely disappeared beneath the waves.
What happened to Doggerland is controversial. Some claim it was suddenly submerged by a tsunami triggered by an underwater landslide just off the coast of Norway 8,200 years ago, while others think it was slowly consumed by rising sea levels.
In reality, it was likely a combination of both. A 2020 study put forward evidence to suggest that Doggerland had already reduced dramatically in size (as a result of rising sea levels) by the time the tsunami hit. Regardless, anyone who lived in Doggerland 8,200 years ago would have probably given everything they had to be anywhere else.
The time when insects were massive
If insects make your skin crawl, then the Carboniferous Period (359 to 299 million years ago) would probably be your idea of hell on Earth. This is a period often referred to as the ‘Age of Giant Insects’, and for good reason – during the Carboniferous, Earth was ruled by bugs many times bigger than any alive today.
The 2m-long, double-duvet sized Arthropleura was the largest of the Carboniferous’ giant bugs. It’s distantly related to today’s millipedes and like its living relatives it also subsisted on a diet of decaying plants and animals. There was also a dragonfly-like insect known as Meganeura that, with a 75cm-wide wingspan, was roughly the same size as a sparrowhawk.
It’s often said that bugs achieved gigantism during the Carboniferous as a result of increased levels of oxygen in the atmosphere, and while this may be true to some degree it’s more likely they grew so large in response to a lack of competition from vertebrates. At this time, vertebrates were still relatively small and largely confined to environments close to water.
As a group, vertebrates were dwarfed and outnumbered by bugs during the Carboniferous, but fast forward a few million years to the Permian Period (299 to 252 million years ago) and they soon emerged as the most dominant forms of life on land. The Permian was a period of great diversification for vertebrates. However, while it may have been evolutionary prosperous for some groups, it ended in disaster for others – but more on that later.
The time fungi towered over everything else
The first kind of life to really gain a foothold on land wasn’t plants, but fungi. The first fungi were relatively small, but they soon paved the way for giants such as Prototaxites. This tree-like organism lived roughly 400 million years ago and formed huge spires that measured up to 1m in diameter and reached heights of more than 8m.
It’s unclear exactly what Prototaxites was; it may have been a fungus, or it may belong to a long-lost group of lichens. Whatever its affinities, Prototaxites was by far the largest land-dwelling organism of its time and towered over everything that attempted to grow in its shadows.
Prototaxites, along with many other early types of fungi, are thought to have been saprotrophic. This is a process whereby fungi release digestive enzymes that break down organic matter, allowing them to extract nutrients from the material they’re growing on. These enzymes are so powerful that, over time, they can break down rock and form fertile soils. It’s this process that researchers think prepared Earth’s surface for the vascular plants that emerged during Prototaxites’ reign
So, why was this a particularly terrible time to be alive? Well, without large networks of plants producing oxygen, levels of it in the atmosphere were a lot lower than they are today. There was also very little to eat, especially if you weren’t a fan of mushrooms.
The time a pandemic lasted 18 million years
From the Early Oligocene (33 million years ago) to the Early Miocene (15 million years ago), an ancient virus known as ERV-Fc plagued dozens of different species of mammals, from dolphins to great apes. The inactive fragments of this virus still live on in many mammals today, including us, and it’s the study of these fragments that have allowed scientists to learn more about it.
ERV-Fc is what’s known as an endogenous retrovirus – a type of virus that infects cells and inserts itself into its host’s DNA. When this happens in reproductive cells, the viral sequence can be passed from parent to offspring. ERVs are very common in the genomes of vertebrates and are estimated to make up nearly 8% of our own genome.
A 2016 study revealed that ERV-Fc independently infected many different groups of mammals, rather than a single shared ancestor. This study also found evidence to suggest that the virus jumped species more than 20 times over the course of an 18-million-year-long pandemic that spread across all continents besides Australia and Antarctica.
It’s unclear exactly how deadly ERV-Fc was, but based on its structure it’s understood to be part of a group of viruses known as gammaretroviruses. Today, this group includes the murine leukemia virus (MuLV) in mice and feline leukemia virus in cats (FeLV), both of which are known to cause cancer.
The time when Earth was ruled by giants
The blue whale (Balaenoptera musculus) may be the largest animal to have ever lived, but on average animals alive today are a lot smaller than those that lived during parts of prehistory.
The Late Jurassic (162 to 143 million years ago) is a period that’s particularly renowned for its giants. It’s often referred to as the ‘Golden Age’ of not only dinosaurs, but pterosaurs and marine reptiles too – wherever you lived during the Late Jurassic, be it on land, in the sky, or in the oceans, a giant, hungry reptile was never too far away.
Some of the largest dinosaurs of the time lived in North America and are known from fossils uncovered from the world famous Morrison Formation. This expansive, dinosaur-bearing rock formation has yielded more than 10 different meat-eating theropods, all of them large enough to hunt human-sized animals.
The king amongst these theropods wasn’t T.rex (that particular species appeared in the Late Cretaceous around 70 million years later), rather Allosaurus – a smaller but arguably more belligerent predator that’s thought to have hunted in packs and been capable of bringing down giant, long-necked dinosaurs known as sauropods. These plant-eating sauropods would have been deadly too, crushing anything unlucky enough to get caught under their feet.
The Late Jurassic may have been a great time to be a giant, but for any animal smaller than a Volkswagen Beetle it would have been particularly terrible.
The time it rained for 2 million years
The Triassic (252 to 201 million years ago) is widely regarded as one of the hottest and driest periods in Earth’s history. However, during this 51-million-year-long period, there was a 2-million-year-long episode when it rained pretty much non-stop.
This is known as the Carnian Pluvial Episode (CPE) and it started roughly 234 million years ago. It’s evidenced by thick layers of river rocks, sediments from giant lakes, and evidence of coal swamps sandwiched in between layers of drier rocks more traditionally associated with the Triassic, such as red sandstones. These peculiar layers are signs of increased rainfall and they’re found all over the world, hinting at a global climate shift.
Some estimates suggest that rainfall quadrupled over this period and as much as 1,400mm of rain was dumped every year – that’s how much a temperate rainforest gets today, but this would have fallen across the entire supercontinent of Pangea!
This massive amount of rain had a profound impact on the animals that lived during the Middle Triassic, particularly the dinosaurs. In rocks dated to the start of the CPE, dinosaurs make up just 5% of the fossils of terrestrial vertebrates. In rocks dated to the end of this episode, they comprise more than 90%.
The dinosaurs’ distant relatives, the crocodile-line archosaurs, didn’t relish the rain quite as much, which is ironic considering the watery habitats their descendants live in today. They experienced huge losses at this time and never again reached the diversity they had during the Early Triassic.
The time an asteroid destroyed a dynasty overnight
Since the emergence of animals some 800 million years ago, Earth has witnessed five major mass extinctions – together these are known as the ‘Big Five’.
The event that wiped out the dinosaurs 66 million years ago wasn’t the most destructive of the five – that title goes to an event discussed later – but it is the one that wiped out entire families of animals and plants in a matter of days, rather than over the course of millennia.
This event, known as the K-Pg mass extinction, was caused by the impact of a giant, 15km-wide asteroid that made landfall in what is now the Yucatán Peninsula in Mexico. Based on fish bones found in the impact’s ejecta layer, it’s thought the impact may have taken place during spring.
The effects of the impact were catastrophic; any animals (or plants) standing within 1,500km at the time of the impact would have been instantly vaporised. Those standing further away weren’t exactly safe and would have arguably faced an even more painful death, being melted by firestorms, catapulted by hurricane-force winds, crushed by blazing debris, or simply suffocated by the poisonous air.
It’s estimated that the energy released during the impact was equivalent to 10 billion Hiroshima bombs.
There were some plucky animals that survived this ‘worst day ever’, including our mammalian ancestors, but when the fires finally burnt themselves out and the dust clouds settled, as many as 75% of species on Earth had disappeared.
The time when humans were prey
We may be firmly at the top of the food chain today, but for the majority of our existence we were prey for many larger, toothier predators.
While they’re not considered a member of our genus (Homo), australopithecines are often referred to as ‘humans’, or at least incredibly close relatives. Later undisputed human species include Homo erectus, Homo neanderthalensis, and – of course – Homo sapiens. These early humans lived alongside some of prehistory’s most terrifying animals, including sabretooth tigers, giant short-faced bears, and baby-eating eagles.
There’s lots of evidence to suggest that early humans were prey for such animals. The most famous example is the 2.8-million-year-old Taung Child – a fossilised skull of a young Australopithecus africanus that bears a puncture wound in each of its eye sockets. These wounds match those made by the talons of a crowned eagle, suggesting the child was killed and carried off by an airborne predator.
There’s gruesome evidence of our distant relatives being hunted by big cats too – the remains of a female Paranthropus robustus found in a cave in South Africa show signs of having been bitten and gnawed on by a leopard.
As humans got larger and, crucially, smarter, it’s likely that more and more predators stopped viewing them as prey. That said, we shouldn’t get too complacent; even today there are animals that, if hungry enough, will target humans, such as tigers, polar bears, and crocodiles.
The time nearly everything died
Known fittingly as the ‘Great Dying’, the End-Permian mass extinction is the third of Earth’s ‘Big Five’ and – in terms of how many species were wiped out as a result – the most destructive. This era-defining event almost ended life on Earth entirely and by some estimations may have consigned as many as 90% of species to extinction!
The impacts of this event were destructive on land, but they were truly cataclysmic in the oceans where entire ecosystems collapsed, never to be seen again. Some of the most diverse groups in preceding periods, such as eurypterids, trilobites, and blastoids, were completely eradicated during this event. Others lost more than 95% of their species (e.g. brachiopods, crinoids, and ammonites) and only narrowly made it through to the following period, the Triassic.
The ‘Great Dying’ is widely considered to have been caused by the eruption of a huge volcanic system that lay under what is now Siberia, Russia. This eruption released huge amounts of greenhouse gases into the atmosphere, which elevated global temperatures and acidified the planet’s oceans. This injection of greenhouse gases raised levels of CO₂ in the atmosphere from 400 ppm to 2,500 ppm. To put that into perspective, current CO₂ levels measure ~430 ppm.
The ‘Great Dying’ didn’t happen overnight like the extinction event that claimed the lives of the dinosaurs; instead it lasted for nearly 50,000 years and may have taken place in several distinct pulses. Staying alive during this time would have been particularly difficult, though it wasn’t impossible and our existence today is proof that some resilient animals made it through.