Freddie Gray, gay marriage, Donald Trump and the Paris attacks. Those were among the biggest news topics of conversation for Americans on Twitter in 2015, according to an analysis by Echelon Insights, a research and intelligence firm.

The company looked at an estimated 459.9 million Twitter mentions to break down the biggest trending topics of the year, week by week. The chart below shows how those topics varied over the year. Most of the topics were political, though the Pluto flyby, Caitlyn Jenner and "the dress" also made a prominent appearance.

The chart below shows how those topics looked in terms of the weekly share of the news conversation. You can see how Iraq/ISIS, Hillary Clinton and Barack Obama remain fairly constant topics of conversation throughout the year, and Donald Trump becomes a big topic after July. In contrast, the conversations about Freddie Gray, Greece and the Paris attacks are all intense but short-lived.

President Obama dominated the conversation as he has in past years, receiving 55 million mentions in 2015. Donald Trump had 43 million U.S. mentions in the year, followed by Hillary Clinton with 31.5 million.

Their tracking also shows some fascinating differences in how topics of conversation differ in various political circles. The charts below show the most talked about stories by everyone, Washington D.C. elites, conservative activists and liberal activists on Twitter.

The analysis also highlights a few of the most notable tweets from 2015, including this tweet by Mitt Romney about the Confederate flag:

And this tweet from President Obama after a Muslim boy was taken into police custody when he brought a clock to school:

Remember Ebola? 2014 probably seems like ages ago, but here's a reminder of what their chart for 2014 looked like, which drew on 184.5 Twitter mentions:

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