It’s generally held that there have been five main mass extinction events on Earth, with huge
percentages of the life on this planet killed off every time. The last one happened some sixty-six
million years ago, to bring about the end of the Cretaceous Period… and the downfall of the
dinosaurs. By now, it’s a well-known story, with the leading theory being that a seven-mile-wide
asteroid crashed into what’s modern day Mexico, to trigger such climate chaos that the non-avian
dinosaurs - huge, imperious creatures that had roamed for 180 million years beforehand - simply
couldn’t survive. There followed the rise of the mammals, and the rest really is history.
And yet, questions still remain about exactly what the world was like before that infamous
rock from space crashed down and changed it all. This is Unveiled, and today we’re answering the
extraordinary question; what was Earth like before the dinosaurs were killed?
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Given that the dinosaurs lived for such a long time, today’s question really spans a
vast stretch of our planet’s natural history. The Mesozoic Era - the “age of the dinosaurs” - is
further split into three periods, the Triassic, Jurassic, and Cretaceous. The Jurassic Period is
generally seen as when dinosaurs were at their strongest, and at the peak of their powers… but
the first examples of these colossal creatures actually emerged millions of years earlier,
in the Middle Triassic. The first dinosaurs arrived, then, around 240 million years ago…
and, as we know, they grew and spread and evolved from that point until their extinction moment,
with the asteroid, sixty-six million years ago. In terms of what the world looked like over all
that time, it certainly underwent massive change… not least because the Age of the Dinosaurs
overlaps with the breakup of Pangea. While it’s easy to view the world map as it is today and
assume that it must’ve always been like that, we know that it certainly wasn’t. And we know that,
during the Triassic Period, almost all of Earth’s land was actually massed together,
as part of the supercontinent Pangea. Pangea spread almost from pole to pole,
meaning that you could feasibly walk from the top of the world to the bottom,
without ever finding your way blocked by water. There were still oceans on Earth, however,
and the majority of the Earth’s surface was still covered by water… it’s just that the ocean
wasn’t split by smaller continents as it is today. Instead, Pangea had epic coastlines running north
to south on either side, and a massive ocean simply ran all around the globe,
from one side to the other. This was the world that dinosaurs
were born into. But, by the end of the Cretaceous Period, Pangea had broken up.
A map of the world sixty-six million years ago is still quite different to today’s… with Africa
much closer to South America, Australia only just beginning to break away from Antarctica,
and modern-day India cut off alone in what’s now the Indian Ocean. But the shapes of the continents
as we recognise them were beginning to form. For the dinosaurs, this of course had an impact.
When dinosaurs first emerged, they all essentially lived on the same land mass. There were weather
differences and localized conditions across Pangea, yes, as well as mountain ranges, rivers,
and other natural borders, but the first dinosaurs were never quite so cut adrift from each other as
the last ones were. By the end of the Cretaceous Period, sixty-six million years ago, there were
dinosaur breeds confined to much smaller land masses than their earliest ancestors had been…
with their homes pushed to different regions of the globe, thanks to plate tectonics.
That said, in terms of pure climate, even at the end of the dinosaurs’ reign, researchers believe
that most of the world will’ve been basking in similar climatological conditions. It’s
generally said that the world was tropical during the time of the dinosaurs. There were certainly
desert regions, including across what’s now North America, but for the most part Earth was warm,
wet, and lush. Even those places furthest north and south, including what’s now Antarctica,
were not stacked with ice as they are today. Meanwhile, it’s been widely documented in
recent years how the air that the dinosaurs breathed was likely much more oxygen-rich,
too, which is one reason specifically why they were able to grow and thrive in the first place.
There are some theories, however, that the climate may well have been changing toward
the end of the Cretaceous Period, and not for the better (from a dinosaur’s point-of-view).
In fact, according to one 2021 study, the changes on Earth just before the asteroid hit
might even have meant that the dinosaurs were soon to die out anyway… it’s just that the asteroid
hurried along the process. So, what’s going on? The multi-authored study first appeared in the
scientific journal, “Nature Communications”, in June 2021, claiming that “dinosaur biodiversity
declined well before the asteroid impact”. The study focuses on six dinosaur types, or families,
known to have existed up until the asteroid fell, making use of the fossil record to estimate
how many of each dinosaur was alive on Earth pre-asteroid, sixty-six million years ago. And,
after a lot of number crunching, the bottom line and lead takeaway from the study is that all
six families were in decline. Some worse than others, but it’s thought that the numbers for
all of them were falling, all over the world map… and that they had been falling steadily for at
least ten million years before the asteroid. The conclusion that this particular study arrives at,
then, is that the dinosaurs may have been going extinct anyway, with or without
the asteroid. The next question is why? The leading theory - and one that’s referred
to within the study itself - points toward the effects of climate change. It’s thought
that average temperatures on Earth had dropped by the end of the Cretaceous Period by almost
eight degrees Celsius. The key thing here is that the dinosaurs were what’s known as mesothermic.
They weren’t quite cold-blooded like most reptiles are, but they weren’t warm-blooded
like mammals, either. Importantly, the mesothermic classification is still debated in the scientific
community… but if we do view dinosaurs as mesotherms, then the drop in global temperature is
likely to have had a major impact on any dinosaur species’ health, as they relied on outside
temperatures to properly function. The study also highlights how “cascade effects” might’ve
been putting pressure on the dinosaur food chain, too. This is when a decline in one dinosaur type
can trigger a decline in another, its predator, which can cause a decline in another, and so on.
Unlike in the Jurassic Period, it seems that the dinosaurs and ecosystems alive in the Cretaceous
simply weren’t as strong. They certainly weren’t robust enough to withstand when the asteroid hit,
but they may have been dying out anyway. In an alternate world where the asteroid didn’t
hit, there’s no way to definitely say whether they would or wouldn’t have survived. History shows us
how various species (of dinosaur and of others) have experienced dwindling numbers before, only
to bounce back and restore stability. Perhaps the dinosaurs could’ve achieved that, too… which could
well have meant that the rise of the mammals would never have taken place, and therefore that we
(human beings) would never have emerged, either. The breakup of Pangea would still have continued,
and the world map would still have gradually formed into the layout that we know today…
it’s just that it would be marked with dinosaur habitats, rather than human towns and cities.
But, of course, in the real world we know that a mass extinction event did take place sixty-six
million years ago. And that, although the effects of it weren’t quite so instantaneous to
kill off every dinosaur at the precise moment the asteroid hit, the resulting, long-term ecological
change and disruption was enough to take these creatures to extinction. Up until that time, the
dinosaurs had overseen massive change on Planet Earth… the breakup of a supercontinent and the
formation of several, smaller landmasses, being the simplest change to visualise. Their typically
tropical landscapes were evolving as well, though, and according to research this might’ve meant that
the dinosaurs’ days were numbered, anyway. A mostly lush and green planet, but one that was
going through some major changes, too. That’s what Earth was like before the dinosaurs were killed.
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