Alternate Timeline/Universe where the extinction level incident that occurred 65 million years ago didn't happen

Question

Disclaimer : I'm working on the entire pseudo-science thing , so the scientific part of this whole thing isn't made up properly... Certain things have not been explained , this is to keep the post short. Also I apologize if I haven't provided any necessary info or if I have broken any guidelines as this is my first post. I realize how this topic could be quite broad. Hence I've given a list of things that are necessary in an answer at the end.

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Scenario : Okay. So here is the background, in the future, a well 200 years or so later, time travel is being developed. The solar system is the only known place in the universe with life. This is restricted to Earth, Mars, Titan and a myriad of larger, sometimes grouped asteroids...

Now the event in focus is time travel experiments which are achieved by a fictional subatomic process to create a wormhole. These experiments are being performed in the outer fringes of the asteroid belt, away from major settlements, as a safety precaution. The time travel works for small massed objects, and trials with life is considered to be too hazardous. The scientists decide to try their experiment with a huge mass object and thus they choose a nearby asteroid for insertion.

The asteroid is inserted into the portal and just before it goes into the portal, the asteroid splits into two segments. Now this method of time travel is still being worked upon, the scientists know that the objects they send in are being sent back into the past... But, they don't know the destination. So, just before the asteroid goes in, it splits into two and one part gets sent back to the past, a little after the formation of animal life on Earth and one part gets sent a little later , to the time of Dinosaurs and it hits the earth , wiping out all larger forms of life.

The scientists are completely oblivious to all of this.. But what they do realize is that insertion into the portal irradiates the inserted object , with an energy equivalent to the mass of the object. Subsequently the experiments are banned and the off-world experimentation site is closed down.

Now back to the part that the scientists don't know. The second segment to enter the portal was responsible for the extinction of the dinosaurs and all other large reptiles... This is timeline 1, where events as we know happen and this is where eventually the time-travel dabbling scientists help create the timeline in a everlasting circle of sorts.

The first segment is more interesting. This piece of the asteroid was significantly larger than the the other one, and collides into the Sun , disrupting the fusion process inside the sun and causing the 'transformation' of hydrogen into something else, caused by the subatomic differences in the asteroids makeup. All the 'polluted matter' of the Sun splits away from the original and creates a small , more-powerful star that orbits the sun, that emits a greater part of the electromagnetic spectrum and bombards the solar system with radiation. This is timeline 2.

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Now The Questions : How would the life on Earth be affected ? Plant life already exists , but most would begin mutate to the new environment. The primary life is reptilian..... Assuming that due to the exposure the life forms have gained the potential for greater intellect what types of creatures would be produced ? What of their society ? Peaceful hunter-gatherers or Tribal fighters ? How would the earth be affected in terms of meteorology and geography ?

Answer 1

Disclaimer:

As noted in my comment on @Greymtr question, I'll propose sets of assumption to make the question's setting more plausible. This is intended to deviate slightly from the questions proposed. The goal is to provide a general idea that could works with our current physics (not the time travel part).

And finally, as per the Question Owner's permission,

‎@HendrikLie Yeah , absolutely . - Greymtr

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Assumptions and suggestions:

1. The secondary star mentioned in the question and its effect is omitted.
2. The first segment of the asteroid in the question is just a normal asteroid segment, containing no handwavium that could damage the sun (ahem).
3. Those two segments are actually dropped on nearly the same time, but in slightly different location and timing, each is dropped in different alternate reality (after all, each time a time travel is performed, new alternative timeline is formed, as hinted in the question).

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The Answer:

So the scientists drops an asteroid that's split to two segments. One is dropped earlier and immediately followed by the second segment.

1. The first segment

This one dropped on an orbit that intersects the yet-to-hit-earth asteroid, and hits it, sent it to a trajectory that directly intersects earth orbit at the same moment earth is on that intersection! This will cause mass extinction that occurred in our timeline. This is timeline 1, and is our timeline.

2. The second segment

Yet in different timeline, this one dropped on an orbit that intersects the yet-to-hit-earth asteroid somewhere in the past. Due to its insertion, it interacts with orbital path of the yet-to-hit-earth asteroid and send it in different orbit that causes the yet-to-hit-earth asteroid never intersects earth orbit. This will be the timeline 2 in the question, but will never hits the sun either, so no secondary star is formed. Because earth's life will never experience mass extinction as in our timeline, according to Axelrod's answer,

The dinosaurs were already on the decline when the asteroid struck.

As mentioned in his(?) answer, upcoming ice ages and environmental changes might force dinosaurs to adapt, yet in different manner that might hinders the evolution of mankind (I just gives you the highlight of Axelrod's answer, as his full answer presents it quite nicely and to avoid redundancy). You might develop alternative intelligent species that's not human (well, it is safe to assume that primates might never evolved in this timeline, so species with similar physiology and body plan like ours is highly unlikely, even if you consider the dinosauroid theory). For cultures and behavior of those new intelligent species, I believe it is wise to assume that theirs are not necessarily similar to us (which I believe that it is your original conception of the possible emerged race). Again, it (the new intelligent species) depends on its origins and diets (and possibly its environment and its social structures).

Consider this: 

1. We as omnivores is advantaged by large range of food that we could eat. Herbivores might support higher population density considering advanced farming (hydroponics, aeroponics, etc). Carnivores, in the other hand, might have sparser population, or even in considerably high population density, they might consider breeding livestocks to support their population, but their population size couldn't be compared to herbivores and omnivores intelligent species.

2. Warm-blooded or cold-blooded species might also affects their daily life, hence affecting their cultures. Warm-blooded species would likely have a constant urge to eat (not the whole day, but warm-blooded species must eat in definitive intervals), as we constantly "burn our food" to generate heats, so their social life might be more active. Expect large range of environment that they could survive on. Cold-blooded species would most likely prefers hotter environment, as their body must be "heated" in the morning by the sunlight or other heat sources. Expect them to be mostly lying, sunbathing at the morning, and is probably active mainly at night or at dusk. Their metabolism is slower, it might affect their social life. Perhaps they'll interact less? Their society might evolve slowly, and also their technology might develop slowly. But that's not a constant.

3. If they dwells on the sea, they would probably never develops civilization, just look at dolphins and humpback whales. They were intelligent (probably more than humans), but they never develops civilization like ours.

4. Consider their development and traits, as even the smallest trait could affect their society and evolution. Just like how we differ from the apes, as we lacks something that they have, and the very same lacks gives us advantage over them.

Conclusion:

There's no need to develops secondary stars that bathes us with radiation to change the entire history. As even the slightest change could changes everything if it diverge earlier enough. This could adds more interesting story to tell, as "the slightest change done far in the past causes the greatest changes that alter the future" (ahem, my prose is not too persuasive and interesting, but you got the idea).‎

Answer 2

Something that's really worth considering is the effect of the second sun. Given the handwavium involved in its creation I'm not going to get into the orbital or physical processes required for it to form, and instead focus on two things.

1: Gravity

Even a small part of the sun splitting off to form a second star would wreak havoc on the orbits of the planets. I'm assuming that it splits into a stable orbiting binary system (which is improbable) and that the smaller star isn't playing tricks with physics. This would throw the orbits of the planets into some sort of weird, complicated pattern that would basically mean kissing goodbye to regular seasons, and possibly even a regular Goldilocks zone.

2: The radiation

The second star is pumping out exotic radiation at a greater rate than the sun. Ignoring the 'exotic' part and just assuming a greater amount of radiation, you need to consider whether the magnetosphere will be sufficient to prevent the atmosphere of the earth being blown off. If it is, you need to consider if the magnetosphere is sufficient to prevent the atmosphere from becoming heavily ionised (ie: lethal). If it is, you need to consider if the amount of energy provided to the earth by the new star is low enough to avoid turning us into a second Venus. Basically, is this new star going to scour the surface of the earth clean with its baleful gaze?

Finally: The effect on life If the planet isn't thrown into a weird eccentric orbit and the planet isn't periodically autoclaved, there isn't a chance that life will evolve as you expect.

Firstly the increased radiation content will cause all manner of mutations, most lethal, leading to an incredibly hardy set of species surviving. Think cockroaches.

Secondly the inevitable climate changes would completely change the evolutionary path of the world, probably to favour high endurance, seasonally robust creatures.

I for one wait for the rise of our Tardigrade overlords. All hail the Prime Waterbear. (Seriously. Look up Tardigrades, they're insane)

Answer 3

Well there's one kink in that plan: The dinosaurs were already on the decline when the asteroid struck.

Moreover, the climate shifts leading to multiple ice ages were unrelated to the collision. As such, the whole reptilian supremacy argument may not work. Instead, birds and eventually mammals would likely have still taken over. That said, dinosaur varieties which were on the decline may have adapted to the coming storm (I.E. growing smaller, becoming warm blooded if they weren't already, getting some sort of insulation), but their presence would still have pushed mammalian evolution down the road a bit (we were, after all, akin to little rodents at the time), possibly enough to have prevented the precise combinations that led to human evolution (whatever those were).

Assuming the dinosaurs did adapt to become smaller and more efficient in the changing world, they likely would have held off a few niche evolutions (like the terror birds and mammalian megafauna), until a new contestant could kick them out. So, there would likely be smaller mammal species than we know of now, due to the competition at the upper size brackets. Birds would still likely have evolved along the same path, but the larger birds, like the terror birds, would likely still be around now (for the record, historically bird > reptile) once they finally took their niche, since there would be no large mammals to compete with.