Submitted by [deleted] t3_10qabyp in explainlikeimfive
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stairway2evan t1_j6owpnh wrote
And our ancestors at the time were the early mammals - smaller, rat-like creatures, and a few other species. They were mostly scavengers who were better able to survive the difficult conditions, while many other animal and plant species died.
As things got better, without giant lizards stomping around everywhere, those mammals were able to thrive, diversify, and spread all over the world into the wide array of mammals we have today. Including the first primates, somewhere around 55 million years ago (well after the meteor extinction event), who would eventually (millions upon millions of years later) give rise to us.
stumpdawg t1_j6oycak wrote
Facts!
makesyoudownvote t1_j6oyvlh wrote
Also worth noting a slight variation on this theory that is the currently held belief.
Unlike most modern reptiles, dinosaurs were actually warm blooded. Opposite of what they used to believe this actually played against them.
It used to be taught that because they were cold blooded they couldn't handle the cold and that's why mammals dominated afterwards. But this as it turns out is not true, they were mostly warm blooded like modern birds.
Being warm blooded means you have a MUCH higher and more demanding metabolism. Snakes for example only need to eat once a month or so to be completely healthy and they can go much longer if needed. Most warm blooded creatures need to eat pretty much daily in order to remain healthy.
When the meteor hit and the ice age started food became much more scarce. Gigantic warm blooded animals simply couldn't eat enough food to survive. Meanwhile some larger reptiles like crocodiles survived precisely because they don't need to eat much, and can go into what is almost a hibernation like state in extreme cold where they can go a really long time without eating. They just stick their noses out of the water and breathe really slowly and can survive even when the water is frozen for several months.
[deleted] OP t1_j6ot8dg wrote
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bachmanity t1_j6p1ua4 wrote
The Fungal Infection Mammalian Selection hypothesis says that the killing mechanism was unchecked fungal infections as the temperature dropped. Modern cold blooded creatures suffer from bone infections if their body temperature stays too low.
RhynoD t1_j6pi2q5 wrote
I think that hypothesis more accurately explains why reptiles did not rise back up to the dominant roles that mammals filled. The fungi were fed in part by the massive die-off of plants and animals following the meteor.
There are also some evidence to suggest that a mass extinction due to natural climate change at the time was already beginning and the meteor cranked what was already a huge ecological upheaval to 11.
ThenaCykez t1_j6ot7c0 wrote
Strictly speaking, it wouldn't have killed every dinosaur, but rather all of the biggest ones, with the smaller ones adapting to climate change and becoming modern birds.
The idea is that the impact of the meteor kicked up so much dust, it would have dimmed the sun and made earth much cooler for a period of time. We already observe this happening on a smaller and shorter scale with major volcano eruptions. As the earth cools and dims, large animals have trouble finding enough vegetation or prey to stay fed and warm, and mass extinctions occur. Smaller animals don't need as much bulk food to survive, and there would have been much more plant matter available once the biggest dinosaurs that used to eat by the ton had starved.
exodus3252 t1_j6oucoi wrote
The ELI5:
- Big rock from sky hit Earth.
- Earth get hot, then super dusty for long, long time. Dusty Earth block light from sun.
- Plants die. Veggy Dinos no longer have lunch. They die.
- Meaty Dinos no longer able to lunch on Veggy Dinos. They die.
- Only tiny flying Dinos survive. Tiny flying Dinos become Birds.
The end.
arcturisvenn t1_j6ou2io wrote
The asteroid hits but that isn't the end of the process. There is evidence to suggest it triggered massive volcanic activity and dramatic climate change. A lot of the extinction doesn't necessarily happen at the moment of impact, but in the many years to follow. It also helps to keep in mind that ecosystems tend to have a domino effect when they collapse: some species going extinct can lead to others going extinction.
Enormous large scale extinction follows the impact, dramatically changing the sorts of species we see in the fossil record. The whole thing is known among scientists as the KT event.
That being said, some dinosaurs did survive, and continued to evolve, and we see their descendants today in birds.
As for us, mammals prior to the KT event were relatively small (think rodent-like). But in the millions of years that follow there was a tremendous evolutionary opportunity with most dinosaurs gone. Mammals gradually evolved into new roles and diversified. Eventually one of those branches gives rise to primates. Out of the primate branch comes apes, and out of the ape branch, humans.
As for why our ancestors didn't go extinct, it's hard to say. But there is no reason to assume they wouldn't. The KT event is a massive extinction event but lots of things survived it.
CheegsFlex t1_j6otapd wrote
Believe it or not, some animals and other organisms survived the mass extinction. Crocodiles, small mammals, and even some tenacious plants, for example, managed to live on after the asteroid impact. Due to this, these generalist plants were tough and started recycling organic matter and creating more biomes to support more types of life again.
breckenridgeback t1_j6ovkil wrote
The impact that killed most of the dinosaurs didn't kill all life on Earth. But the dinosaurs were very large animals high on the food chain, and when food chains collapse, those animals are the first to go. Smaller animals, like the ancestors of the mammals that dominate the planet today, had an easier time surviving.
It also didn't kill all of the dinosaurs. We know the survivors as "birds".
ScienceIsSexy420 t1_j6ov1v2 wrote
There have been 5 mass extinction events in our planet's history, with the death of the dinosaurs being the most recent. This particular event, caused by an asteroid impact as others have noted, led to the death of about 76% of all species on earth and all nonavian dinosaurs. Fun fact: many scientists claim we are in the middle of the 6th mass extinction event, this one caused by humans. It's called the anthropocene
grumblingduke t1_j6p8ag4 wrote
Around 75% of all plant and mammal species were made extinct by the "K-Pg extinction event" that happened 66 million years ago. Very few large animal species (Wikipedia gives a maximum mass of 25kg) survived - some crocodiles and turtles being the exceptions.
While we tend to think of extinction events as being sudden and immediate (which they are on evolutionary or geological scales), the K-Pg extinction event is thought to have lasted anywhere from a few years to 10,000 years, before things stabilised (similar to the mass-extinction event the Earth is currently going through; hard to notice on a day-to-day basis or year-to-year, but definitely noticeable over thousands of years). A meteor didn't just crash and kill and the dinosaurs - a meteor crashed and caused massive, long-term changes to global climates and ecosystems that lasted thousands of years, and most large animal species didn't survive.
In terms of what happened, the main thing was anywhere up to 2 years of global darkness caused by all the dust and other matter thrown up into the sky by the initial crash. This would have killed off a huge chunk of plant life (which requires photosynthesis to live), as well as likely making things colder. Without plants, animals that lived off plants would gradually die off, and without them animals that lived off other animals would slowly die off - including the big super-predators and super-herbivores like the larger dinosaurs (who would have needed to eat a lot of stuff). Many individuals would survive for a while, maybe some generations, but over time the species wouldn't, as not enough would be around to maintain a stable population.
On top of that, you have a huge chunk of weird minerals and materials being thrown up into the atmosphere, to settle across the globe, some of which would be toxic to some animals and plants. There's also a good chance that some of these minerals settled into the oceans, significantly increasing the acidity of the oceans, making them uninhabitable for a lot of plants and animals, and generally messing up the world's water supply.
Things that survived were generally things with the ability to survive long periods without food (like crocodiles), things that lived off detritus (all the dead plant and animal matter caused by the destruction) like worms, snails and insects, and the smaller animals that lived off them (like the surviving birds and mammals).
And as the dust settled (both figuratively and literally) there was an explosion of diversity in life - with so many evolutionary niches now opened up, mammals in particular flourished, evolving in all sorts of new ways (including getting larger and smarter).
Some dinosaurs did survive. We just don't generally call them dinosaurs any more, but birds.
[deleted] OP t1_j6otjzb wrote
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stumpdawg t1_j6osnr9 wrote
The meteor threw a shitload of water and earth into the atmosphere causing an ice age.
Not all life was wiped out, just the ones that couldn't cope with the cold like the larger dinosaurs (if they were all wiped out we wouldn't have birds)