The Dow's transformation: A look at the companies that have joined and departed on the journey to 40,000

• On Thursday, the Dow reached a significant milestone as it surpassed 40,000 for the first time.
• The economy has evolved significantly since the index was first created, resulting in a marked difference in its appearance today.

The stock market reached a significant milestone, marking a century-long climb that has seen a constantly evolving portfolio of stocks.

Although the closely followed average on Thursday surpassed the 40,000 marker for the first time in history, the index today appears vastly different from its state a century ago, or even just a few decades ago.

In 1896, Charles Dow introduced the average, which initially consisted of 12 industrial stocks. The Dow was intended to provide a broader gauge of the economy when paired with the index. Over time, the Dow grew to include eight additional stocks in 1916 and 10 more in 1928. Today, the Dow stands at 30 members, having remained a vital indicator of the economy for nearly a century.

The stock market has seen changes in the presence of companies over time, with technology being a prime example. Currently, there are seven tech stocks in the index, indicating its growing significance in the corporate world and equity market.

The esteemed group of blue-chip stocks is governed by a committee, according to S&P Dow Jones Indices. Though there are no defined rules, the committee typically analyzes a firm's reputation, growth over a long period of time, and relevance to investors. Additionally, a sector's representation in the Dow compared with its place in the broader market can also play a role.

The S&P 500 index includes only utility and transportation stocks, not utility or transportation stocks.

CNBC examined the companies that made up the Dow index during significant moments in the past.

1972: Dow hits 1,000

Despite the recent accomplishment, the Dow was below 1,000 until the early 1970s.

In 1972, 10 days after Richard Nixon won the presidential election, the stock index broke above its level on November 14th, and finished the year with a gain of over 14%.

In the year when "Rocket Man" and "Lean on Me" were chart-toppers and "The Godfather" was in theaters, industrial and material stocks still made up a significant portion. Some companies like General Foods and International Harvester were acquired or no longer exist. However, a few companies such as and remain part of this group.

1995: Dow cracks 5,000

It wasn't until the mid 1990s that the Dow would crack 5,000.

Although the Dow reached this level on Nov. 20, 1995, it wasn't officially closed above it until Nov. 21 of that year.

Since 1975, 1995 was the Dow's best year with a gain of more than 33%, and it remains its sixth best year in history. Black Monday, the stock market crash of 1987, had already passed its tenth anniversary at this point.

In 1995, "Clueless" and "Toy Story" were popular among American youth, while Oasis released "Wonderwall." At this time, with the inclusion of stocks like and , approximately half of the index's members had been part of it.

1999: Dow touches 10,000

Within just four years, the Dow hit another key price: 10,000.

On March 29, 1999, the average first touched the level, but it took several days of choppy trading for the index to close a session above 10,000.

As the new millennium approached, Americans were both excited and concerned about the potential for a "Y2K" glitch. Meanwhile, the publication of the book version of "The Perks of Being a Wallflower" added to the excitement and anticipation of the upcoming year.

In March 1999, the dot-com bubble reached its peak, leading to a major market crash a year later. At the time, tech companies had not yet become a significant part of the Dow, with key names like Amazon and eBay not yet earning a spot. Additionally, Sears and Union Carbide were still members of the Dow.

2017: Dow breaks 20,000

Before the Dow reached 20,000, the market would need to overcome two significant obstacles.

The dotcom bubble and the Global Financial Crisis greatly influenced the economic landscape of the 2000s. However, following a steady climb during the early to mid 2010s, the index reached a significant milestone on January 25, 2017.

After Donald Trump's inauguration as president, the Dow finished the year with a return of more than 25%.

Several tech names were added to the Dow by 2017, including important stocks like , , and .

2020: Dow surpasses 30,000

The index was trading at a lower point by almost 10,000 points less than its current value less than four years ago.

On Nov. 24, 2020, the Dow surpassed 30,000 for the first time as the pandemic continued to shape American life. Prior to that, Joe Biden had been elected to succeed Trump as president. The Dow ended 2020 with a gain of over 7%.

In 2020, with many workers and students working remotely due to health concerns, technology's importance increased. One of the latest developments was cloud software, which replaced the long-standing indexed software.

On this day in 2020, all but one member of the group is still present.

2024: Dow eclipses 40,000

In a few more years, the Dow will have another achievement: reaching 40,000.

Despite some challenges, the Dow experienced a rebound in 2023, erasing the losses it suffered in 2022, which was its worst year since 2008.

The surge in the stock market this year has been fueled by investor enthusiasm for artificial intelligence, and a group of large technology companies known as the Magnificent 7 have been attributed with a significant impact on the market's upward trajectory.

E-commerce giant was swapped in for Walgreens earlier this year to make the Dow what it is today.